Method and system for extrusion-based 3D printing of functionally graded articles

Abstract

The present invention discloses a slurry feedstock, a method for preparing the same, and a method and system for extrusion-based 3D printing and / or casting of functionally graded articles under low pressure and room temperature. The slurry feedstock includes a build material including metal, ceramic, or any combination thereof, an organic polymer binder, an additive, and a volatile organic solvent. The build material mixed with the additive and the organic polymer binder dissolved in the volatile organic solvent form a first premix and a second premix, respectively. They are mixed to form a substantially uniform and flowable slurry mixture for producing an article.

Description

[Technical field]

[0001] The present invention relates generally to the field of additive manufacturing and / or mold casting. More specifically, the present invention relates to a slurry feedstock, a method for preparing the slurry feedstock, and a method and system for extrusion-based 3D printing and / or casting of functionally graded articles under low pressure and room temperature. [Background technology]

[0002] Additive manufacturing, also known as 3D printing, is a transformational method for industrial production that creates three-dimensional objects or parts from digital files. This technology allows the creation of solid objects in 3D and therefore complex parts. Typically, thin layers of material are deposited to create complex shapes that cannot be produced by traditional techniques such as casting, forging, and machining. 3D printing is considered one of the key innovative industrial processes for the next few years. It is a very interesting and profitable market in the investment community, offering endless options for companies and industries around the world.

[0003] One of the major advances in additive manufacturing is the ability to produce Functionally Graded Materials (FGMs). FGMs have their structural properties varied along their quantities and properties of the two raw materials mixed together. In contrast, traditional composites are homogeneous mixtures and therefore they require a compromise between the desired properties of the constituent raw materials. As the majority of FGMs contain pure forms of each component, the need for a compromise between the desired properties of the constituent raw materials is eliminated. The properties of both components can be exploited to their full potential. For example, ceramics can be mixed with metals to form the final FGM article without compromising the toughness of the metal side or the fire resistance of the ceramic side. Traditionally, laser powder deposition and solid powder forging have been utilized to produce FGMs. Other traditional manufacturing methods include in-situ processing techniques such as laser cladding, sparging, precipitation, and solidification.

[0004] Among additive manufacturing techniques, vat photopolymerization, where ultraviolet light forms chains between molecules of a liquid light-curing resin, crosslinking and solidifying the resin, is used to create FGM parts or articles. Laser-based processes such as selective laser sintering and selective laser melting, and fused deposition modeling, can also be used to deposit materials, layer upon layer, in various geometric shapes (i.e., adding material to create an object). Interestingly, a common feature of these additive manufacturing techniques is that the variation in material properties is limited to only one spatial dimension with a discrete form, usually toward the print direction or up the z-axis. These techniques, unfortunately, do not address FGMs and their echoes well. Moreover, vat photopolymerization and FDM are primarily involved in printing thermoplastic or plastic composites (with a solid feedstock form), a larger drawback that reduces and further weakens their versatility. Another major drawback of many conventional 3D printing techniques is that they allow only one material to be printed at a time by placing successive layers of material, limiting many potential applications that require the integration of different materials with varying constituents in the same object, such as FGM articles. As an additional drawback, conventional 3D printing using solid feedstocks does not allow for in-situ mixing of material components as the article is printed. Therefore, it is desirable to develop new feedstocks and additive manufacturing techniques that can produce FGM articles with variations or gradients across two or more axes.

[0005] Casting, on the other hand, is basically done by pouring a liquid material, usually molten metal, into a mold cavity that has the shape of the desired part. The liquid material is then cooled, usually by radiating heat through the mold, until it solidifies into the desired shape. Although it may sound simple, casting is generally a very complicated process due to the complex metallurgy that uses molten metal. Casting processes can be divided into expendable and permanent mold processes. In expendable mold processes, the mold (typically made from sand, gypsum and ceramics) is broken to remove the casting. In contrast, in permanent mold processes, the mold (typically made from a metal that retains its strength at high temperatures) is reused and must therefore be designed to allow the casting to be easily removed.

[0006] One of the challenges with traditional casting is the need to melt the metal to a molten state before it can flow into the mold cavity. Such melting processes have the disadvantage of requiring higher energy to produce extremely high temperatures depending on the melting point of the metal used. Additionally, while the molten metal can be pulled down by gravity, a significant amount of pressure must be applied or exerted to actually force the molten metal throughout the mold cavity. Unfortunately, other casting methods such as powder injection molding have similar high pressure demands where the mold itself must be subjected to very high pressures, plus high tooling costs and long setup lead times. It is therefore desirable to develop new, greener feedstock and mold casting techniques that allow for the production of metal / ceramic articles with significantly reduced energy demands and tooling costs.

[0007] By way of background, US 2014 / 0087210 A1 (hereafter '210) discloses a method for making metal or ceramic parts, such as cutting or forming tools, from at least two separate powdered precursors. In '210, the method includes forming a first mixture of composite particles of tough coated hard powder (TCHP) made by encapsulating extremely hard core particles, a very tough binder, multi-type coated particles such as structural materials, and at least one support powder such as a carbide, typically WC-Co. According to '210, the mixture is formed into a green body and sintered to form a functionally graded or multi-component article. WO 2018 / 009593 A1 (hereafter '593) discloses several methods for making metal objects. These methods, according to the '593 publication, generally involve adding a metal powder slurry to a sacrificial mold, such as a mold created by 3D printing, and heating the slurry / mold mixture. In the '593 publication, the heating step may include a step of hardening the slurry to create a green part in the mold, a debinding step of burning off the mold and binder to create a brown part, a sintering step, and a hot isostatic pressing step. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2014 / 0087210(A1) [Patent Document 2] International Publication No. 2018 / 009593(A1) Summary of the Invention [Problem to be solved by the invention]

[0009] For the reasons stated above and others that will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved feedstocks for use in producing FGM articles having different material variations in one or more dimensions of their volume, where the gradual variations may be realized as linear or continuous property variations and / or discrete variations between two layers that also have distinct, well-defined and compatible properties. There is also a need for improved feedstocks, mold casting techniques, and systems thereof for use in casting metal / ceramic articles under additive manufacturing techniques, low pressure and room temperature. While similar feedstocks and techniques for producing such feedstocks may exist in the prior art, for many practical purposes there is still room for significant improvement. [Means for solving the problem]

[0010] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

[0011] Accordingly, the present invention provides a slurry feedstock for extrusion-based three-dimensional (3D) printing of functionally graded articles.

[0012] The slurry feedstock of the present invention comprises a build material comprising metal, ceramic, or any combination thereof, porous, non-porous, or any combination thereof, in an amount of 10% to 90% by volume, an organic polymer binder selected from the group comprising cellulose esters, cellulose ethers, and derivatives thereof, in a concentration of 150 g / L to 550 g / L, an additive selected from the group comprising plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, foaming agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof, and a volatile organic solvent, wherein the build material is a volatile organic solvent. The method may be characterized by mixing a material and the additive to form a first premix and dissolving the organic polymer binder in the volatile organic solvent to form a second premix, respectively, and mixing them to form a substantially uniform, flowable slurry mixture that is printed as a precursor part of the functionally graded article, and the organic polymer binder is debonded from the precursor part by one or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce the final part comprising the build material that selectively varies gradually in composition, configuration including packing pattern, or any combination thereof across a volume of the final part of the functionally graded article in one or more directions.

[0013] Preferably, the metal is selected from the group including ferrous metals, non-ferrous metals, ferrous metal alloys, and non-ferrous metal alloys.

[0014] Preferably, the ceramic is selected from the group consisting of clay, cordierite ceramic, steatite, stoneware, earthenware, porcelain, kaolin, quartz, silicates, camot, bentonite, and mullite; oxide ceramics including alumina, zirconia including zirconia stabilized in yttria (Y3O2), beryllium oxide, yttrium oxide, titanium oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, uranium oxide (UO2), plutonium dioxide (PuO2), yttrium barium copper oxide, spinel, magnetoplumbite, perovskite, and tialite; titanium carbide, boron carbide, non-oxide ceramics including tungsten carbide, carbide ceramics including silicon carbide, silicon nitride, boron nitride, aluminum nitride, aluminum oxynitride, nitride ceramics including SiAION; bioceramics including hydroxyapatite (HAP), tricalcium phosphate (TCP), amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), tetracalcium phosphate monoxide (TetCp), biphasic calcium phosphate (BCP), and any combination thereof.

[0015] Preferably, the construction material contains a particle mesh size of 300 μm or less.

[0016] Preferably, the cellulose ester is selected from the group including cellulose acetate, cellulose acetate phthalate, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose butyrate, cellulose tributyrate, cellulose acetate propionate, cellulose propionate, cellulose tripropionate, cellulose nitrate, cellulose acetate propionate, carboxymethyl cellulose acetate, carboxymethyl cellulose acetate propionate, carboxymethyl cellulose acetate butyrate, cellulose acetate butyrate succinate, cellulose propionate butyrate, and mixtures thereof.

[0017] Preferably, the cellulose ether is selected from the group comprising methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose, hydrophobically modified ethyl hydroxyethyl cellulose, hydrophobically modified hydroxyethyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, carboxyalkyl hydroxyalkyl cellulose, and mixtures thereof.

[0018] Preferably, the organic polymeric binder has a number average molecular weight of 150,000 or less.

[0019] Preferably, the volatile organic solvent is selected from the group comprising ketones including acetone, butanone, methyl ethyl ketone, methyl amyl ketone, methyl isobutyl ketone and cyclohexanone; aliphatic hydrocarbons; aromatic hydrocarbons; alcohols including methanol, ethanol, propanol, isopropyl alcohol and butanol; methyl formate; ethylene carbonate; propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, 1,2-dimethoxyethane, gamma-butyrolactone, ethyl acetate, isopropyl acetate, ethyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, nitromethane, acetonitrile, methylcyclohexane, n-heptane, n-hexane, cyclohexane, dipropylene glycol n-butyl ether, and mixtures thereof.

[0020] Preferably, the substantially homogeneous, flowable slurry mixture comprises two or more substantially homogeneous, flowable slurry mixtures, each comprising a respective first premix and a respective second premix.

[0021] Preferably, the two or more substantially uniform, flowable slurry mixtures are instantaneously mixed in situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

[0022] Preferably, this second premix is ​​in an amount of 10% to 90% by volume.

[0023] Preferably, the slurry feedstock further comprises a support material that forms a substantially uniform, flowable support mixture configured to print support structures for the overhanging or cantilevered portions of the functionally graded article.

[0024] Preferably, the support material comprises a ceramic, a sacrificial material, a dissipative material, or any combination thereof.

[0025] Preferably, the sacrificial material is debonded from the prior component in either or both of a pyrolysis process and a solvent debonding process.

[0026] Preferably, the dissipative material is debonded from the prior component in either or both of a pyrolysis process and a solvent debonding process.

[0027] According to a second aspect of the present invention, there is provided a method of preparing a slurry feedstock for extrusion-based three-dimensional (3D) printing of functionally graded articles.

[0028] The preparation method of the present invention includes the steps of providing a build material comprising a metal, a ceramic, or any combination thereof, the build material being porous, non-porous, or any combination thereof, providing the build material in an amount of 10% to 90% by volume, providing an organic polymer binder selected from the group comprising cellulose esters, cellulose ethers, and derivatives thereof, the organic polymer binder being provided in a concentration of 150 g / L to 550 g / L, and providing a plasticizer, defoamer, dispersant, sacrificial material, dissipative material, scaffold material, water soluble inorganic salt, foaming agent, graphene, graphene oxide, flame retardant, toner, release additive, stabilizer, antistatic agent, impact modifier, colorant, antioxidant, and any combination thereof. preparing an additive selected from the group including a combination of a build material and a volatile organic solvent; mixing the build material and the additive to form a first premix; mixing an organic polymer binder and a volatile organic solvent to form a second premix; and mixing the first premix and the second premix to form a substantially homogenous, flowable slurry mixture that is printed as a precursor part of the functionally graded article, wherein the organic polymer binder is debonded from the precursor part by one or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce a final part comprising the build material that selectively varies gradually in composition, configuration including packing pattern, or any combination thereof, across a volume of the final part of the functionally graded article in one or more directions.

[0029] Preferably, the method includes forming two or more substantially homogenous, flowable slurry mixtures, each comprising a respective first premix and a respective second premix.

[0030] Preferably, the method includes the step of instantaneously mixing two or more substantially homogenous, flowable slurry mixtures in situ with a static or dynamic mixer to form one substantially homogenous, flowable slurry mixture.

[0031] Preferably, the method includes providing a support material that forms a substantially homogenous, flowable support mixture configured to print a support structure for the overhang or cantilever portion of the functionally graded article.

[0032] According to a third aspect of the present invention, there is provided a method for extrusion-based three-dimensional (3D) printing of a functionally graded article.

[0033] The printing method of the present invention includes providing a slurry feedstock comprising: providing a build material comprising a metal, a ceramic, or any combination thereof, the build material being porous, non-porous, or any combination thereof; providing the build material in an amount of 10% to 90% by volume; providing an organic polymer binder selected from the group comprising cellulose esters, cellulose ethers, and derivatives thereof, the organic polymer binder comprising providing the organic polymer binder in a concentration of 150 g / L to 550 g / L; and providing an organic polymer binder selected from the group comprising plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, blowing agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof. providing a slurry feedstock comprising: preparing an additive to be added to the build material; preparing a volatile organic solvent; mixing the build material and the additive to form a first premix; mixing an organic polymer binder and a volatile organic solvent to form a second premix; mixing the first premix and the second premix to form a substantially uniform, flowable slurry mixture to be printed as a precursor part of the functionally graded article; debinding the organic polymer binder from the precursor part by one or both of a pyrolysis process and a solvent debinding process; and subjecting the precursor part with the organic polymer binder debound to a sintering process to produce a final part comprising a build material that selectively varies gradually in composition, configuration including packing pattern, or any combination thereof across a volume of the final part of the functionally graded article in one or more directions.

[0034] Preferably, the method includes forming two or more substantially homogenous, flowable slurry mixtures, each comprising a respective first premix and a respective second premix.

[0035] Preferably, the method includes the step of instantaneously mixing two or more substantially homogenous, flowable slurry mixtures in situ with a static or dynamic mixer to form one substantially homogenous, flowable slurry mixture.

[0036] Preferably, the method includes the step of providing a support structure for the overhanging or cantilevered portion of the functionally graded article, the support structure comprising a substantially homogenous, flowable support mixture formed by a support material.

[0037] According to a fourth aspect of the present invention, there is provided a system for extrusion-based three-dimensional (3D) printing of functionally graded articles.

[0038] The system of the present invention includes one or more vessels that contain a slurry feedstock, the slurry feedstock comprising a build material, which may be metal, ceramic, or any combination thereof, and may be porous, non-porous, or any combination thereof, in an amount of 10% to 90% by volume; an organic polymer binder selected from the group including cellulose esters, cellulose ethers, and derivatives thereof, in a concentration of 150 g / L to 550 g / L; and a plasticizer, defoamer, dispersant, sacrificial material, dissipative material, scaffolding material, water soluble inorganic salt, foaming agent, graphene, graphene oxide, etc. and an additive selected from the group consisting of an organic polymer binder, a flame retardant, a toner, a mold release additive, a stabilizer, an antistatic agent, an impact modifier, a colorant, an antioxidant, and any combination thereof; and a volatile organic solvent, wherein the build material and the additive are mixed to form a first premix and the organic polymer binder is dissolved in the volatile organic solvent to form a second premix, and the mixed premixes form a substantially uniform and flowable slurry mixture, the system regulating injection of a slurry feedstock contained in one or more vessels, and comprising a solenoid valve, a mechanical pump, and combinations thereof. a computing unit having a jetting adjusting means selected from the group and a controller configured to generate a control signal for the jetting adjusting means, the controller being connected to a database comprising a predetermined set of materials and rheological profiles for which the control signal is to be operatively influenced on a final part of the functionally graded article; a fluid driver configured to provide fluid pressure to the slurry feedstock contained in the one or more vessels or the jetting adjusting means to effect movement of the slurry feedstock contained in the one or more connected vessels to provide a pressurized slurry feedstock, the fluid driver being selected from the group comprising a pneumatic driver, a hydraulic driver, a mechanical moving device, and any combination thereof; and a printhead operatively driven by the computing unit and configured to jet a substantially homogenous and flowable slurry mixture to create a precursor part of the functionally graded article, the organic polymer binder being debonded from the precursor part by one or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to form a composition comprising a packing pattern across the volume of the final part in one or more directions;or any combination thereof to produce a final part that includes a selectively graded build material.

[0039] Preferably, the system includes a static or dynamic mixer that instantaneously mixes two or more substantially homogenous, flowable slurry mixtures in situ to form one substantially homogenous, flowable slurry mixture prior to transfer to the printhead.

[0040] Preferably, the system includes a static or dynamic mixer that instantaneously mixes two or more substantially homogenous, flowable slurry mixtures in situ to form one substantially homogenous, flowable slurry mixture prior to transfer to the printhead.

[0041] Preferably, one or more containers contain support material that forms a substantially uniform, flowable support mixture that prints support structures for the overhanging or cantilevered portions of the functionally graded article via said printhead or other printheads.

[0042] According to a fifth aspect of the present invention, there is provided a slurry feedstock for casting articles at low pressure and room temperature.

[0043] The slurry feedstock of the present invention comprises a build material, which may be porous, non-porous, or any combination thereof, including metal, ceramic, or any combination thereof, in an amount of 10% to 90% by volume; an organic polymer binder, selected from the group including cellulose esters, cellulose ethers, and derivatives thereof, in a concentration of 50 g / L to 550 g / L; and a plasticizer, defoamer, dispersant, sacrificial material, dissipative material, scaffolding material, water soluble inorganic salt, foaming agent, graphene, graphene oxide, flame retardant, toner, release additive, stabilizer, antistatic agent, impact modifier, colorant, antioxidant, and any combination thereof. and an additive selected from the group, and a volatile organic solvent, wherein the build material and the additive are mixed to form a first premix and the organic polymer binder is dissolved in the volatile organic solvent to form a second premix, and then mixed to form a substantially homogenous and flowable slurry mixture for casting in a cavity of a mold substantially immersed in a solidification bath for producing a precursor part of the article by phase inversion, the organic polymer binder being debonded from the precursor part by either or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce the final part of the article.

[0044] According to a sixth aspect of the present invention, there is provided a method of preparing a slurry feedstock for casting an article at low pressure and room temperature.

[0045] The method of the present invention includes providing a build material comprising a metal, a ceramic, or any combination thereof, the build material being porous, non-porous, or any combination thereof, providing the build material in an amount of 10% to 90% by volume; providing an organic polymer binder selected from the group comprising cellulose esters, cellulose ethers, and derivatives thereof, the organic polymer binder being provided in a concentration of 50 g / L to 550 g / L; and providing a plasticizer, defoamer, dispersant, sacrificial material, dissipative material, scaffold material, water soluble inorganic salt, foaming agent, graphene, graphene oxide, flame retardant, toner, release additive, stabilizer, antistatic agent, impact modifier, colorant, or the like. preparing an additive selected from the group consisting of antioxidants, antioxidants, and any combination thereof; preparing a volatile organic solvent; mixing the build material and the additive to form a first premix; mixing the organic polymer binder and the volatile organic solvent to form a second premix; and mixing the first premix and the second premix to form a substantially homogenous and flowable slurry mixture for casting in a cavity of a mold substantially immersed in a solidification bath for producing a precursor part of an article by phase inversion, wherein the organic polymer binder is debonded from the precursor part by either or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce a final part of the article.

[0046] According to a seventh aspect of the present invention, there is provided a method for casting an article at low pressure and room temperature.

[0047] The method of the present invention includes providing a slurry feedstock comprising the steps of providing a build material, the build material being porous, non-porous, or any combination thereof, providing the build material in an amount of 10% to 90% by volume; providing an organic polymer binder selected from the group including cellulose esters, cellulose ethers, and derivatives thereof, providing the organic polymer binder in a concentration of 50 g / L to 550 g / L; providing an additive selected from the group including plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, blowing agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof; and providing a volatile organic solvent. mixing the blended build material and additives to form a first premix; mixing the dissolved organic polymer binder and a volatile organic solvent to form a second premix; mixing the first premix and the second premix to form a substantially homogenous and flowable slurry mixture; subjecting the substantially homogenous and flowable slurry mixture to casting in a mold; and immersing the mold having a cavity filled with the substantially homogenous and flowable slurry mixture in a solidification bath to produce a precursor part of the article by phase inversion; debinding the organic polymer binder from the precursor part by one or both of a pyrolysis process and a solvent debinding process; and subjecting the precursor part debound of the organic polymer binder to a sintering process to produce a final part of the article.

[0048] According to an eighth aspect of the present invention, there is provided a system for casting an article at low pressure and room temperature.

[0049] The system of the present invention includes one or more vessels for receiving a slurry feedstock, the slurry feedstock comprising: a build material, including metal, ceramic, or any combination thereof, porous, non-porous, or any combination thereof, in an amount of 10% to 90% by volume; an organic polymer binder selected from the group including cellulose esters, cellulose ethers, and derivatives thereof, in a concentration of 50 g / L to 550 g / L; an additive selected from the group including plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, foaming agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof; and a volatile organic solvent, wherein the build material and the additives are mixed together. and dissolving an organic polymer binder in a volatile organic solvent to form a first premix and a second premix, respectively, and mixing them to form a substantially homogenous and flowable slurry mixture, the system comprising: a mold configured to cast the substantially homogenous and flowable slurry mixture contained in one or more containers; a solidification bath configured to substantially immerse the mold having a cavity filled with the substantially homogenous and flowable slurry mixture therein to produce a precursor part of the article by phase inversion; and a debinding means for debinding the organic polymer binder from the precursor part, the debinding means comprising one or both of a pyrolysis process and a solvent debinding process followed by a sintering process to produce a final part of the article.

[0050] The above and other objects, features, aspects and advantages of the present invention will be better understood by carefully reading the detailed description provided below with appropriate reference to the accompanying drawings.

[0051] The invention will become more fully understood and many of the attendant advantages thereof will be readily appreciated by considering the following detailed description, when taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0052] [Figure 1]1 illustrates a configuration for dual material printing according to one embodiment of the present invention. [Diagram 2] FIG. 1 illustrates a setup for dual-material printing, where Material A refers to a first substantially homogeneous and flowable slurry mixture (e.g., metal as the build material) according to one embodiment of the present invention, and Material B refers to a second substantially homogeneous and flowable slurry mixture (e.g., ceramic as the build material) according to one embodiment of the present invention. [Figure 3A] 1A-1D are side and top views of a functionally graded article fabricated using a slurry feedstock through extrusion-based three-dimensional (3D) printing according to one embodiment of the present invention, where Material A refers to a first substantially homogeneous and flowable slurry mixture (e.g., metal as a build material) according to one embodiment of the present invention, and Material B refers to a second substantially homogeneous and flowable slurry mixture (e.g., ceramic as a build material) according to one embodiment of the present invention. [Figure 3B] 1A-1D are side and top views of a functionally graded article fabricated using a slurry feedstock through extrusion-based three-dimensional (3D) printing according to one embodiment of the present invention, where Material A refers to a first substantially homogeneous and flowable slurry mixture (e.g., metal as a build material) according to one embodiment of the present invention, and Material B refers to a second substantially homogeneous and flowable slurry mixture (e.g., ceramic as a build material) according to one embodiment of the present invention. [Figure 4] FIG. 1 illustrates the porosity gradient of a porous functionally graded article fabricated using a slurry feedstock by extrusion-based 3D printing in accordance with one embodiment of the present invention. [Figure 5A] FIG. 1 is a perspective view of a functionally graded article manufactured using a slurry feedstock through extrusion-based 3D printing, where Material A denotes a first substantially homogeneous and flowable slurry mixture (e.g., metal as a build material) according to one embodiment of the present invention, and Material B refers to a second substantially homogeneous and flowable slurry mixture (e.g., ceramic as a build material) according to one embodiment of the present invention. [Figure 5B]FIG. 5B is a cross-sectional view of the functionally graded article along line AA in FIG. 5A, where material A represents a first substantially uniform and flowable slurry mixture (e.g., a metal as a building material) according to one embodiment of the present invention, and material B represents a second substantially uniform and flowable slurry mixture (e.g., a ceramic as a building material) according to one embodiment of the present invention. [Figure 6A] FIG. 13 is a photograph showing a cross section of a concentric green part that is a functionally graded article produced by extrusion-based 3D printing from a slurry feedstock of one embodiment of the present invention. [Figure 6B] FIG. 13 is a photograph showing a cross section of a concentric green part that is a functionally graded article produced by extrusion-based 3D printing from a slurry feedstock of one embodiment of the present invention. [Figure 6C] FIG. 7 illustrates a gradient transition in the xy plane of a first layer of the green component of FIGS. 6A and 6B according to one embodiment of the present invention. [Figure 6D] FIG. 7 illustrates a gradient transition in the xy plane of the second layer of the green component of FIGS. 6A and 6B in one embodiment of the present invention. [Figure 7] 1 is a flow chart illustrating an approach for preparing a slurry feedstock for extrusion-based 3D printing of a functionally graded article in accordance with one embodiment of the present invention. [Figure 8] 1 is a flowchart illustrating an approach for extrusion-based 3D printing of a functionally graded article in accordance with one embodiment of the present invention. [Figure 9A] FIG. 1 illustrates a system setup for extrusion-based 3D printing of a functionally graded article of one embodiment of the present invention. [Figure 9B] FIG. 1 illustrates a mechanism for extrusion-based 3D printing of a functionally graded article in accordance with one embodiment of the present invention. [Figure 10] FIG. 1 illustrates a first system, a second system, and a third system employed for extrusion-based 3D printing of functionally graded articles using a slurry feedstock of one embodiment of the present invention. [Figure 11]FIG. 1 illustrates a first system, a second system, and a third system employed for extrusion-based 3D printing of functionally graded articles using a slurry feedstock of one embodiment of the present invention. [Figure 12] FIG. 1 illustrates a first system, a second system, and a third system employed for extrusion-based 3D printing of functionally graded articles using a slurry feedstock of one embodiment of the present invention. [Figure 13] FIG. 1 illustrates a first system, a second system, and a third system employed for extrusion-based 3D printing of functionally graded articles using a slurry feedstock of one embodiment of the present invention. [Figure 14] FIG. 2 illustrates a packing pattern and its density for use in a functionally graded article of one embodiment of the present invention. [Figure 15] FIG. 13 shows a support feature printed on a platform for the overhang or cantilever portion of a functionally graded article of one embodiment of the present invention. [Figure 16] FIG. 1 illustrates a first configuration for printing support structures for overhanging or cantilevered portions of the functionally graded article using a single print head or nozzle, where Material A refers to a first substantially uniform, flowable slurry mixture (e.g., metal as a build material) according to one embodiment of the present invention, Material B refers to a second substantially uniform, flowable slurry mixture (e.g., ceramic as a build material) according to one embodiment of the present invention, and Material C refers to a substantially uniform, flowable support mixture, where Materials A, B and C are mixed in a single static or active mixture according to one embodiment of the present invention. [Figure 17]FIG. 13 illustrates a second configuration for printing support structures for the overhanging or cantilevered portions of the functionally graded article using two print heads or nozzles, where material A represents a first substantially uniform, flowable slurry mixture (e.g., a metal as a build material) according to one embodiment of the present invention, material B represents a second substantially uniform, flowable slurry mixture (e.g., a ceramic as a build material) according to one embodiment of the present invention, and material C refers to a substantially uniform, flowable support mixture, where materials A and B are mixed in a single static or active mixture according to one embodiment of the present invention and material C is directed to the other print head. [Figure 18] FIG. 1 illustrates a system employed for extrusion-based 3D printing of a functionally graded article that requires a support structure for its overhang or cantilever and uses a slurry feedstock, in accordance with one embodiment of the present invention. [Figure 19] FIG. 1 illustrates a reusable mold according to one embodiment of the present invention, comprising a first part having a cavity recessed or formed therein and a second part removably encasing the first part, the cavity containing a single substantially homogenous, flowable mixture according to one embodiment of the present invention. [Figure 20] FIG. 2 illustrates the cavity of the mold of FIG. 1 adapted to accommodate two substantially homogeneous and flowable mixtures according to one embodiment of the present invention. [Figure 21] FIG. 2 illustrates the cavity of the mold of FIG. 1 adapted to receive two substantially uniform and flowable mixtures using a static or dynamic mixer according to one embodiment of the present invention. [Figure 22] 2 is a flow chart illustrating a technique for preparing a slurry feedstock for casting an article under low pressure at room temperature in accordance with an embodiment of the present invention. [Figure 23] 1 is a flow chart illustrating a technique for casting an article under low pressure at room temperature in accordance with an embodiment of the present invention. [Figure 24] FIG. 6 is a block diagram illustrating a technique for casting an article under low pressure at room temperature (as described in FIG. 5 ), according to one current embodiment. [Diagram 25] 1 is a diagram showing a direct printing system according to an embodiment of the present invention. [Figure 26] FIG. 1 is a diagram showing a configuration of a multi-material printer according to an embodiment of the present invention. [Figure 27] FIG. 1 is a diagram showing a configuration of an in-situ mixing printer according to an embodiment of the present invention. [Figure 28] 1 is a flowchart illustrating a process involving 3D printing an article according to one embodiment of the present invention. [Figure 29] FIG. 1 illustrates a thermal debinding and sintering profile according to one embodiment of the present invention. [Diagram 30] FIG. 2 is a side view of a stainless steel based feedstock print according to one embodiment of the present invention. [Diagram 31] FIG. 1 is a perspective view of a stainless steel based hardened article according to one embodiment of the present invention. [Diagram 32] FIG. 1 is a perspective view of a stainless steel-based sintered article according to one embodiment of the present invention. [Diagram 33] FIG. 2 is a side view of a ceramic-based stock print according to one embodiment of the present invention. [Diagram 34] FIG. 1 is a perspective view of a ceramic-based cured product according to one embodiment of the present invention. [Diagram 35] FIG. 1 is a perspective view of a ceramic-based sintered product according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] It should be noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention.

[0054] The present invention discloses a slurry feedstock for use in extrusion-based three-dimensional (3D) printing of functionally graded materials, which are functionally graded materials (FGMs), methods for preparing the same, methods for extrusion-based 3D printing of articles, and systems therefor. Advantageously, by subjecting the slurry feedstock to extrusion-based 3D printing, the present invention produces FGM articles comprising materials that selectively vary in composition, composition, including packing pattern, or any combination thereof, gradually across the volume of the final part in one or more directions, including in a three-dimensional (3-axis) fashion. Such FGM articles produced by the present invention surprisingly exhibit linear or continuous characteristics, e.g., changes in composition, composition, including packing pattern, or any combination thereof, and / or discrete gradual changes, in one or more directions, between two layers that also have distinct, well-defined, and interchangeable properties. Moreover, the present invention can be used and maintained in a very specific, compact, cost-effective, fast, and simple manner without the use of complex and sophisticated processes, components, or parts (e.g., feedstock heaters, etc.).

[0055] Essentially, the functionally graded articles, or articles known as FGM articles, of the present invention relate to heterogeneous articles characterized by a gradual change in their multiphase properties (i.e., microstructure and mechanical properties such as tensile strength, thermal conductivity, Young's modulus, etc.). Traditionally, FGM manufacturing techniques can be classified according to thin and bulk FGM. In the former case, thin FGMs are typically formed by surface coating or deposition techniques. In the latter case, manufacturing techniques for bulk FGMs include powder metallurgy, centrifugal methods, and additive manufacturing. In additive manufacturing, bulk FGMs can be formed by vat photopolymerization processes, laser-based processes such as selective laser sintering (SLS) and selective laser melting (SLM), or fused deposition modeling (FDM). These traditional methods can only change material properties within a single dimensional space, usually along the print direction or z-axis. In contrast, FDM and vat photopolymerization are mostly, if not entirely, used exclusively for thermoplastic or plastic composite printing. These conventional methods are unable to print FGM articles that have variations in composition, structure, fill pattern, and / or properties across planes in three-dimensional (3D) space (wherein a Cartesian coordinate system is based on three mutually perpendicular coordinate axes, i.e., x-axis, y-axis, and z-axis), or variations in at least one type of build material, e.g., metal or ceramic.

[0056] The term "slurry" as used herein refers to a solid-fluid mixture, including both solid-liquid and solid-gas mixtures. For convenience, the present invention will be discussed with respect to solid-liquid slurries as feed compositions in which the solids and liquids are in separate phases. Solid-liquid slurries also include solids and liquids that are introduced into the system of the present invention and that are fully or partially separated.

[0057] The term "feedstock" as used herein is defined as a raw material or mixture of raw materials having suitable properties to be fed into the present system capable of producing a functionally graded or FGM article, and is to be interpreted as components that are not yet mixed or that are being further mixed to produce a mixture suitable for injection into the system.

[0058] As used herein, the term "premix" refers to ingredients that are mixed together and form one portion of the mixture that makes up the slurry mixture.

[0059] The term "fill pattern" or "structural fill" as used herein refers to a pattern that leaves void spaces within the interior and / or exterior of a functionally graded article. The pattern is preferably invisible. The pattern includes, but is not limited to, lines, zigzag structures, lattice structures, triangular structures, cage structures, honeycomb structures, 3D honeycomb structures, cube structures, cube subdivision structures, octet structures, gyroid structures, star structures, octagram spiral structures, Archimedes chord structures, Hilbert curve structures, linear structures, concentric structures, or any combination thereof. The fill pattern is preferably formed using an adaptive fill printing process.

[0060] As used herein, the term "three-dimensional printing" or "3D printing" refers to printing by extrusion through a print nozzle (i.e., extrusion-based 3D printing), or a process that provides a three-dimensional part or object that extends in three directions (e.g., length, width and height) on a flat surface, plate or substrate.

[0061] As used herein, the terms "precursor part" or "green part" refer to a functionally gradient article article or preform in a pre-sintered state produced by the present invention for further processing by other manufacturing techniques.

[0062] As used herein, the term "brown part" refers to a functionally graded article produced from a predecessor or green part that has been subjected to a pyrolysis and / or solvent debonding process to remove binders, sacrificial materials and / or dissipative materials that previously held the feedstock together. The brown part may be further heated to fully sinter the part or subjected to sintering to produce the final or finished part of the functionally graded article.

[0063] The term "varied" or "variation" as used herein is a broad term and is used in its ordinary sense, including, but not limited to, the divergence or magnitude of variation from a point, line, or data set. In one embodiment, the composition and / or structure of the build material in the final part of the functionally graded material can have a variation, including a range outside of a reference or data set that represents a range of possibilities based on a known or standard 3D printing material. This term can encompass positive variation, negative variation, and neutral variation. A positive variation can indicate a positive deviation beyond the reference or data set. A negative variation can indicate a negative deviation that fails to achieve the reference or data set. A neutral variation can indicate zero variation of the composition and / or structure of the build material relative to the reference or data set, e.g., no transition gradient.

[0064] According to one preferred embodiment of the present invention, the slurry feedstock comprises a build material, an organic polymer binder, additives (which may be optional), and a volatile organic solvent. In this regard, the organic polymer binder dissolves in the volatile organic solvent, thus creating an organic polymer binder solution. The additives are added to the build material to obtain predetermined rheological behavior and print characteristics. The slurry feedstock can essentially be formed by blending said organic polymer binder solution with said build material mixed with additives. The resulting slurry feedstock can be printed and dried at room temperature without external heat supply means.

[0065] The build material of the present invention refers to a powder that is preferably used to form a slurry feedstock and from which a functionally graded article is built in the system for extrusion-based 3D printing of the present invention. The powder, or powders referred to as particulate materials or particles, have various mesh sizes. In one embodiment, the build material has a particle size of about 300 μm or less, preferably less than about 200 μm. The build material is preferably a layer-forming material for use in the system for extrusion-based 3D printing of the present invention. The build material may also be in various shapes, such as granular powder, fibrous powder, and scaly powder. In a preferred embodiment, the build material is used in an amount of about 10% to about 90% by volume, more preferably about 30% to about 90% by volume.

[0066] The building material preferably comprises a metal, a ceramic, or any combination thereof. In one embodiment of the present invention, the building material may be porous, non-porous, or any combination thereof. For example, porous metal refers to metal particles having significant porosity, e.g., porosity greater than about 0.5 cc / g. The building material may have pores less than 100 μm (microporous) and / or greater than 100 μm (mesoporous). On the other hand, non-porous metal refers to metal particles having little or no porosity, e.g., porosity less than about 0.05 cc / g. Porous ceramics preferably have porosity with controllable porosity and good mechanical properties. The term "porosity" as used herein refers to the volume fraction of void space in a porous article, e.g., its porous building material.

[0067] The porous metals and / or porous ceramics used in the present invention are preferably microporous and can be produced, for example, by direct foaming using suitable foaming agents, sacrificial materials, dissipative materials, skeletal materials, etc. Porosity can also be controlled by the size of salt crystallizations.

[0068] In a preferred embodiment of the present invention, the build material may include only metal (porous and / or non-porous) or ceramic (porous and / or non-porous). Also, the build material may include combinations of metal and ceramic in a predetermined mixing ratio or volume percentage to suitably meet the desired properties of the build material for the functionally graded article. Examples of such combinations include metal and ceramic; porous metal and ceramic; metal and porous ceramic; porous metal, non-porous metal and ceramic; metal, porous ceramic and non-porous ceramic; porous metal, non-porous metal, porous ceramic and non-porous ceramic, etc. Various other combinations (e.g., first metal, second metal, first ceramic, second ceramic, etc.) are contemplated.

[0069] The metals used in the present invention are preferably selected from the group comprising ferrous metals, non-ferrous metals, ferrous metal alloys, and non-ferrous metal alloys.

[0070] The ferrous metal is selected from steel, stainless steel, mild steel, cast iron, malleable iron, ductile cast iron, and the like. The ferrous metal preferably includes iron, iron-chromium alloys, iron-chromium-nickel alloys, iron-chromium-zinc alloys, iron-chromium-aluminum alloys, iron-chromium-magnesium alloys, iron-chromium-lead alloys, iron-aluminum alloys, iron-zinc alloys, stainless steel, iron-nickel alloys, and combinations thereof. Preferred examples of steel and / or stainless steel materials include AISI 304, AISI 304L, AISI 316, AISI 316L, AISI 430, AISI 630 (17-4PH), and AISI 631 (17-7PH). Other steel materials such as A2-A5, D2, H13, M2, and 4140 can also be used in the present invention.

[0071] The non-ferrous metals are selected from aluminum, aluminum alloys, magnesium, magnesium alloys, zinc, zinc alloys, cadmium, chromium (III), copper, copper (II) cadmium, lead, cobalt, cobalt chromium, cobalt chromium molybdenum, nickel, nickel alloys, molybdenum, titanium, tantalum, niobium, silver and gold. Preferred examples of aluminum and / or aluminum alloys include AlSi10Mg, AlSi7Mg, ADC12 and AlMg5Mn. Preferred examples of nickel alloys include alloy 706, alloy 718, alloy 625, alloy 725 and invar types such as FeNi36 or 64FeNi, or Hastelloy X, Hastelloy C and Kovar.

[0072] The ceramics used in the present invention are preferably selected from the group comprising silicate ceramics, oxide ceramics, non-oxide ceramics, bioceramics, and any combination thereof.

[0073] The silicate ceramic preferably includes, but is not limited to, clay, cordierite ceramic, steatite, stoneware, earthenware, porcelain, kaolin, quartz, silicate, camot, bentonite, mullite, and any combination thereof.

[0074] The oxide ceramics preferably include, but are not limited to, alumina, zirconia including zirconia stabilized in yttria oxide (YO), beryllium oxide, yttrium oxide, titanium oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, uranium oxide (UO), plutonium dioxide (PuO), barium yttrium copper oxide, spinel, magnetoplumbite, perovskite, tialite, and any combination thereof.

[0075] Non-oxide ceramics preferably include, but are not limited to, carbide ceramics such as titanium carbide, boron carbide, tungsten carbide, silicon carbide, nitride ceramics such as silicon nitride, boron nitride, aluminum nitride, aluminum oxynitride, nitride ceramics including SiAION (ceramics based on the elements silicon (Si), aluminum (Al), oxygen (O) and nitrogen (N)), and any combination thereof.

[0076] The bioceramic is preferably a calcium phosphate ceramic, including, but not limited to, hydroxyapatite (HAP), tricalcium phosphate (TCP), amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), tetracalcium phosphate monoxide (TetCp), biphasic calcium phosphate (BCP), and any combination thereof.

[0077] The build materials of the present invention may include other sinterable materials that do not crack, sag, or delaminate, such as glass powder, acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyether ether ketone (PEEK).

[0078] The organic polymer binder used in the present invention preferably has at least two pyrolysis temperatures. In pyrolysis, decomposition products that can act as reducing agents (i.e. functionally graded articles) are formed when the organic polymer binder is heated at these temperatures. The organic polymer binder is preferably selected so as not to inhibit the reaction between the powder, i.e. metal and / or ceramic particles. The organic polymer binder preferably decomposes or evaporates at temperatures below its corresponding pyrolysis temperature.

[0079] The organic polymer binder is preferably selected from the group including cellulose esters, cellulose ethers, and derivatives thereof. The organic polymer binder is preferably used at a concentration of about 150 g / L to about 550 g / L, more preferably about 200 g / L to about 500 g / L. In various embodiments of the present invention, the number average molecular weight of the organic polymer binder is about 150,000 or less, more preferably about 100,000 or less.

[0080] The cellulose ester is preferably selected from the group comprising cellulose acetate, cellulose acetate phthalate, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose butyrate, cellulose tributyrate, cellulose acetate propionate, cellulose propionate, cellulose tripropionate, cellulose nitrate, cellulose acetate propionate, carboxymethyl cellulose acetate, carboxymethyl cellulose acetate propionate, carboxymethyl cellulose acetate butyrate, cellulose acetate butyrate succinate, cellulose propionate butyrate, and mixtures thereof.

[0081] Cellulose ester derivatives can be prepared by esterification of cellulose.Preferred cellulose ester derivatives include cellulose acetate, butyrate, benzoate, phthalate and anthranilic acid esters, preferably cellulose acetate phthalate (CAP), cellulose acetate butyrate (CAB), cellulose acetate trimellitate (CAT), hydroxypropyl methylcellulose phthalate (HPMCP), succinoyl cellulose, cellulose fluorate, cellulose carbanilate and mixtures thereof.

[0082] The cellulose ether is preferably selected from the group comprising methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose, hydrophobically modified ethyl hydroxyethyl cellulose, hydrophobically modified hydroxyethyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, carboxyalkyl hydroxyalkyl cellulose, and mixtures thereof.

[0083] The cellulose ether derivatives can be prepared by carboxymethylation, carboxyethylation and carboxypropylation. Examples of preferred cellulose ether derivatives include, but are not limited to, nanocellulose, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (NaCMC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), ethylcellulose (EC), tritylcellulose, etc.

[0084] Some organic polymer binders may use cationic cellulose derivatives. Some of the organic polymer binders may include alginates, starches, polysaccharides such as chitin and chitosan, agarose, hyaluronic acid, and derivatives or copolymers thereof (e.g., graft copolymers, block copolymers, random copolymers), or mixtures thereof.

[0085] The additives used in the present invention may be added to the build material and its organic polymer binder to achieve any desired properties, such as desired physical, mechanical, and thermal properties in the slurry feedstock. In a preferred embodiment of the present invention, the additives are selected from the group including plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water-soluble inorganic salts, foaming agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof. The additives are preferably used in an amount of about 1% to about 15% by volume. It is understood that the amount of additives may vary outside of said ranges depending on the specific type of additive selected in the present invention.

[0086] By plasticizer, it is preferred to mean a substance added to the slurry feedstock to improve workability, flexibility and plasticity.Preferably, the plasticizer comprises an additive selected from the group comprising dibutyl phthalate, diaryl phthalate, diethyl phthalate, dimethyl phthalate, dihexyl phthalate, di-2-methoxyethyl phthalate, triphenyl phthalate, (dipropylene glycol) butyl ether, dibutyl tartrate, diethylene glycol monoricinoleate and other phthalates, cetyl alcohol, stearyl alcohol, cetostearyl alcohol, natural or synthetic waxes selected from the group consisting of beeswax, candelilla wax, shellac wax, carnauba wax, petroleum wax, or mixtures thereof, glycerol, triethyl citrate, acetyl triethyl citrate, ethyl o-benzoyl benzoate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, N-ethyl toluene sulfonamide, o-cresyl p-toluene sulfonate, triethyl phosphate, triphenyl phosphate, and any combination thereof.

[0087] The defoamer is a material that eliminates bubbles, preferably by reducing the surface tension of the slurry feedstock. The defoamer serves to change the surface properties of metals and ceramics and reduce the interfacial tension of volatile organic solvents to eliminate foam. The defoamer is preferably selected from the group including polyethylene glycol, polypropylene glycol copolymer, alkyl polyacrylate, polydimethylsiloxane (silicone oil), ethylene bisstearamide (EBS), paraffin wax, ester wax, fatty alcohol wax, white oil or vegetable oil, wax with long chain fatty alcohol, fatty acid soap, ester, polyether modified polysilane and trialkane / alkene phosphate and mixtures thereof.

[0088] The dispersant is preferably a component that acts to maintain the metal and ceramic mutually dispersed in the slurry. The dispersant is preferably a compound selected from the group consisting of silicate compounds, sodium polycarbonate, and alcohol.

[0089] The sacrificial material is preferably a material that, if present in the green or brown part prior to sintering, is not present, at least in the same form and in any significant amount, in the fully sintered body (i.e., the final part) formed upon sintering of the brown part into the final functionally graded article or final part. In one embodiment, the sacrificial material forms a layer on the green or brown part and is later removed to leave a void. The sacrificial material may comprise aluminum orthophosphate, which upon elevated temperature during the sintering process first forms a liquid phase in the green or brown part and then vaporizes or decomposes as one or more gaseous by-products, leaving the green or brown part. The sacrificial material preferably comprises paraffin wax.

[0090] The dissipative material is preferably a material that can act as a mold for casting the ceramic and / or metal parts into the three-dimensional shape of the functionally graded article and can then be removed from the ceramic and / or metal parts by dissolving, melting and / or evaporating without damaging the ceramic and / or metal cast parts. The dissipative material used in the present invention may be a rubber or plastic material selected to achieve desired properties such as thermal expansion and / or dissipative behavior (relative to the ceramic or metal core material).

[0091] In one embodiment, the sacrificial material, the dissipative material, or a combination thereof is removed from a predecessor part or a predecessor part from which the polymer binder has been debonded by pyrolysis, solvent debonding, or any combination thereof (i.e., brown part). The pyrolysis can be preferably selected from the group including heating, thermal debonding, densification / sintering, partial or complete melting of the sacrificial material and / or dissipative material other than the build material, i.e., metal and / or ceramic particles. The solvent debonding may include immersing the predecessor part, brown part, and / or final part in a solvent that dissolves the sacrificial material and / or dissipative material. The distortion can be better controlled and the debonding time can be significantly reduced. The solvents include, but are not limited to, alternative solvents such as n-hexane, heptane, paint thinner, acetone, methyl ethyl ketone, carbon tetrachloride, trichloroethylene, methylene chloride, and supercritical carbon dioxide, as well as water.

[0092] The scaffolding material is preferably a buttress material to provide mechanical integrity to the slurry feedstock. The scaffolding material may be selected from the group including gel-like materials such as chitosan, fibrin, modified alginates, tough materials such as polycaprolactone and other plastics, and slurries containing ceramic and other powders, hydroxyapatite, or tricalcium phosphate. The scaffolding material may also include polycaprolactone, polylactic acid, polyglycolic acid, and poly(lactide-co-glycolide).

[0093] The water-soluble inorganic salts used in the present invention are preferably selected from the group comprising nitrates, borates, chlorates, perchlorates, sulfates, halide salts, sodium carbonate, potassium carbonate, silicates, phosphates, salts of Group I elements, ammonium salts and combinations thereof. In one embodiment, the water-soluble inorganic salt comprises a rare earth metal chloride.

[0094] Foaming agent or blowing agent refers to a component or combination of components capable of forming a foam, preferably generally a cellular foam, preferably in the slurry feedstock, particularly the metal and / or ceramic of the construction material. Foaming agents may be solid, liquid, or supercritical materials.

[0095] In a preferred embodiment of the invention, the blowing agent is a thermally decomposable agent that is liquid or solid at room temperature, has a decomposition temperature below the melting temperature of the build material, and when heated above its decomposition temperature, decomposes while generating a gas such as nitrogen, carbon dioxide or ammonia. The blowing agent may be selected from the group including azodicarbonamide and / or metal salts thereof, hydrazodicarbonamide, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, trihydrazino-sym-triazine, p-oxybisbenzenesulfonylhydrazide, dinitrosopentamethylenetetramine, azobisisobutyrodinitrile, toluenesulfonylhydrazide, p-toluenesulfonylhydrazide, benzenesulfonylhydrazide, bisbenzenesulfonylhydrazide, p,p'-oxybis(benzenesulfonylhydrazide), azobisisobutyronitrile, barium azodicarboxylate, and combinations thereof. The polysaccharide foaming agent preferably includes arrowroot flour, tapioca starch, potato starch, wheat, rice, and corn flour. The amount of foaming agent can be determined according to the desired expansion coefficient.

[0096] The graphene used as an additive in the present invention is preferably a polycyclic aromatic compound formed by covalently bonding multiple carbon atoms. The covalently bonded carbon atoms form a 6-membered carbon ring as a repeating unit, and may further include a 5-membered carbon ring and / or a 7-membered carbon ring. In the present invention, graphene is not limited to single-layer graphene, but also includes, for example, multi-graphene having up to 10 single-layer graphene layers. Graphene preferably includes pure or natural graphene in addition to modified graphene such as graphene oxide or amide-modified graphene.

[0097] Graphene oxide, also known as "graphitic acid" and "graphite oxide", may include, but is not limited to, structures in which oxygen-containing functional groups, such as carboxyl, hydroxyl, or epoxy groups, are attached to the graphene in varying proportions, and may be obtained by treating graphite with a strong oxidizing agent. In one embodiment of the present invention, the graphene oxide includes nanocomposites comprising graphene oxide. Graphene oxide also includes reduced graphene oxide, i.e., graphene oxide in reduced form, e.g., graphene oxide that has been subjected to a reduction treatment to be partially or substantially reduced. Reduced graphene oxide also refers to graphene oxide in which the percentage of oxygen has been reduced by reduction treatment.

[0098] Other additives such as flame retardants, toners, mold release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and mold release agents may be used in the present invention.

[0099] The volatile organic solvent is chemically inert to the build material, but is preferably evaporated or released by the system of the present invention during or after printing. The volatile organic solvent is necessary to completely dissolve the components of the slurry feedstock other than the build material (e.g., organic polymer binder), and also acts as a wetting agent to prevent clogging of the print nozzles of the printhead of the present system. It is also desirable to use a volatile organic solvent that promotes variability (changes) of the build material (i.e., metals and ceramics) in the composition of the functionally graded article, its structure including the fill pattern, or any combination thereof, has a relatively high flash point, and has a relatively low odor. The volatile organic solvent is preferably a solvent that has a low vapor pressure, preferably greater than about 0.133 mbar or 13.3 Pa (0.1 mmHg) at about 20°C.

[0100] The volatile organic solvent is preferably used in an amount of about 1% to about 50% by volume. In one embodiment of the present invention, an appropriate amount of the volatile organic solvent should be used in the organic polymer binder, taking into consideration the preferred or desired concentration of the resulting solution as the second premix, which is the organic polymer binder solution.

[0101] The volatile organic solvent is preferably selected from the group comprising ketones including acetone, butanone, methyl ethyl ketone, methyl amyl ketone, methyl isobutyl ketone and cyclohexanone, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols including methanol, ethanol, propanol, isopropyl alcohol and butanol, methyl formate, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, ethyl acetate, isopropyl acetate, ethyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, nitromethane, acetonitrile, methylcyclohexane, n-heptane, n-hexane, cyclohexane, dipropylene glycol n-butyl ether, and mixtures thereof.

[0102] In various embodiments of the present invention, the build material mixed with the additive preferably forms a first premix, and the organic polymer binder dissolved with or in a volatile organic solvent (i.e., the organic polymer binder solution) forms a second premix. The first premix and the second premix are preferably mixed to form a substantially uniform, flowable slurry mixture, which is then printed as a precursor part of the functionally graded article. The second premix is ​​preferably in an amount of about 10% to about 90% by volume, more preferably about 10% to about 70% by volume.

[0103] The mixing preferably forms or creates a substantially homogeneous and flowable slurry mixture that is printed in the system as a precursor part of the functionally graded article. Thus, Figures 3A and 3B, 4, 5A and 5B are diagrammatic representations of a functionally graded article produced by the present invention. The substantially homogeneous and flowable slurry mixture of the present invention can refer to a composition that is homogeneously mixed in the same state with substantially one morphological phase, such that at least two random samples of the composition have roughly or substantially the same amount, concentration and distribution of the components (e.g., build material, organic polymer binder, additives, and / or volatile organic solvent) therein. The substantially homogeneous and flowable slurry mixture of the present invention is also meant to encompass compositions having components (e.g., build material, organic polymer binder, additives, and / or volatile organic solvent) that are flowable under gravity and / or can be pumped (pumped). The substantially homogeneous and flowable slurry mixture also exhibits the ability of the composition to be transported by gravity or conventional mechanical, hydraulic, or pneumatic pumping means from a containment vessel such as a container.

[0104] In one preferred embodiment, the substantially uniform and flowable slurry mixture comprises two or more substantially uniform and flowable slurry mixtures. As shown in FIG. 2, the two or more substantially uniform and flowable slurry mixtures are mixed in-situ in a static or dynamic mixer instantaneously to form one substantially uniform and flowable slurry mixture. The two or more substantially uniform and flowable slurry mixtures preferably comprise two substantially uniform and flowable slurry mixtures, each comprising a first premix and a second premix. For example, there are two substantially uniform and flowable slurry mixtures, i.e., a first substantially uniform and flowable slurry mixture and a second substantially uniform and flowable slurry mixture. The first substantially uniform and flowable slurry mixture comprises a first premix comprising a metal, which is a construction material, preferably mixed with a dispersant, which is an additive, and a second premix comprising a cellulose ester, which is an organic polymer binder, dissolved in acetone, which is a volatile organic solvent. The second substantially homogeneous and flowable slurry mixture preferably comprises a first premix comprising a ceramic build material mixed with an additive blowing agent and a second premix comprising said organic polymer binder cellulose ether dissolved in a volatile organic solvent butanone. The resulting first and second substantially homogeneous and flowable slurry mixtures are mixed in said single static or dynamic mixer to form a single substantially homogeneous and flowable slurry mixture prior to extrusion.

[0105] The term "in-situ" will be understood to mean the location where mixing occurs or provides for mixing, or on-site mixing. Thus, to form a slurry feedstock at the mixing site, the build material, organic polymer binder, additives and / or volatile organic solvents are generally co-injected (co-delivered) or otherwise provided together in a single static or dynamic mixer (destination site) and mixed or assembled at the co-injection site within the single static or dynamic mixer.

[0106] It will also be understood that the term "instantaneous" or "instantaneous" refers to the time required to mix the build material, organic polymer binder, additives, volatile organic solvent, build material mixed with additives, and / or said organic polymer binder dissolved with or in a volatile organic solvent (i.e., organic polymer binder solution) to prepare the slurry feedstock in the single static or dynamic mixer. In the present invention, such instantaneous mixing may occur in a time period of one to several seconds. Compared to the total time of the process (up to several minutes), mixing on the order of a few seconds can be considered very rapid or instantaneous.

[0107] It should be further understood that the term "single static or dynamic mixer" as used herein refers to a single unit of static or dynamic mixer, and not multiple non-operably linked random mixers, as in the prior art.

[0108] In various embodiments of the present invention, the organic polymer binder is debonded from the prior component in a pyrolysis process, preferably based on the pyrolysis temperature, a solvent debonding process, or a combination thereof. The pyrolysis process can be selected from the group including heating the component other than the build material, i.e., other than the metal and / or ceramic particles, thermal debonding, densification / sintering, partial or complete melting, and / or potentially post-densification annealing, to relieve or further increase residual stresses in the prior component. In some embodiments, the pyrolysis process of heating can be effected at room temperature or at lower temperatures and shorter times than normal heat treatment times and temperatures, e.g., from about 60° C. to about 200° C., for about 10 minutes to about 1 hour.

[0109] Said solvent debonding treatment of the precursor part may comprise contacting the precursor part with a solvent to extract the soluble binder (along with additives, if any) from the body. Solvents suitable for solvent debonding according to the present invention preferably include acetone, methyl ethyl ketone, heptane, carbon tetrachloride, trichloroethylene, methylene chloride and alternative solvents such as, for example, supercritical carbon dioxide, and water.

[0110] The pyrolysis process and / or the solvent debonding process of the precursor part is followed by a sintering process to produce a final part of the functionally graded article. The final part preferably comprises a build material that selectively varies gradually in composition, configuration including packing pattern, or any combination thereof, across the volume of the final part in one or more directions forming a three-dimensional structure. The change in composition, configuration including packing pattern, or any combination thereof, is preferably gradual, referring to a change or deviation that occurs continuously or in small steps over a non-zero distance within the volume. The one or more directions preferably include any spatial direction (x, y, and / or z) in space relative to the reference point system of the functionally graded article.

[0111] The slurry feedstock of the present invention preferably further comprises a support material that preferably forms a substantially homogenous, flowable support mixture configured to print support structures for overhanging or cantilevered portions of a functionally graded article, the support structures being an essential part of enabling the production of complex geometric shapes using additive manufacturing.

[0112] A support structure or support layer is typically built under an overhang or in a cavity of the predecessor part of the functionally graded article being formed that is not supported by the part material itself. The support structure may be built utilizing the same deposition technique as the substantially uniform and flowable slurry mixture is deposited. The host computer may generate additional geometric shapes that act as support structures for the overhang or free space portions of the predecessor part of the functionally graded article being formed. The support material is then deposited during the printing process from the same print head (similar to the substantially uniform and flowable slurry mixture) or from another print head or nozzle according to the generated geometric shapes. The support material can be printed using a single nozzle or multiple nozzle configurations. The support material adheres to the part material during manufacturing and is removable from the finished predecessor part of the functionally graded article when the printing process is completed.

[0113] The support material preferably comprises a ceramic, a sacrificial material, a dissipative material, or any combination thereof. In one embodiment of the present invention, the support material preferably has a particle size greater than about 75 μm. According to one exemplary embodiment, the ceramic, sacrificial material, and / or dissipative material preferably form a first premix, and the organic polymer binder is dissolved with a volatile organic solvent to form a second premix. The first premix and the second premix are added together to form a substantially homogenous and flowable support mixture.

[0114] The pyrolysis and / or solvent debonding and / or sintering processes preferably can inhibit bonding between the support structure and the preceding part of the functionally graded article, so that the sintered functionally graded article can be easily removed from its support structure.

[0115] In one embodiment of the present invention, for a metal-based functionally graded article, it is preferable to use a substantially uniform and flowable ceramic as the support material. The relatively coarse ceramic powder forming the support material results in a loosely packed structure after sintering, which is brittle and does not fuse well with the functionally graded article. Therefore, minimal effort is required to remove the support structure from the functionally graded article. In one embodiment of the present invention, for a ceramic-based functionally graded article, it is preferable to use a substantially uniform and flowable sacrificial material, such as an inorganic salt, as the support material. The support material can be easily removed during a solvent debinding process using water. The precursor part of the functionally graded article is then embedded in a relatively coarse alumina powder for pyrolysis and sintering to form the final functionally graded article.

[0116] Figures 6A, 6B, 6C, and 6D exemplarily show green samples or parts of functionally graded articles produced according to the present invention. In these figures, the green part shows a unique FGM transition gradient that changes in a continuous transition of a spiral concentric shape in the xy plane and z direction. It preferably starts from a base with 10% alumina slurry mixture and 90% clay slurry mixture, smoothly transitions to a middle part with 90% alumina slurry mixture and 10% clay slurry mixture, and then reaches a top part with 10% alumina slurry mixture and 90% clay slurry mixture. The darker and lighter shades of the green part in Figures 6A and 6B indicate clay-based and alumina-based mixtures, respectively. The following configurations may be practical to achieve the green part.

[0117] Table 1: Composition of the first mixture [Table 1]

[0118] Table 2: Composition of the second mixture [Table 2]

[0119] Referring to FIG. 7, a method of preparing a slurry feedstock for use in extrusion-based 3D printing to manufacture a functionally graded article preferably includes the following steps. (a) preparing a build material comprising a metal, a ceramic, or any combination thereof; (a-1) providing a build material, which may be porous, non-porous, or any combination thereof; (a-2) supplying the building material in an amount of 10% by volume to 90% by volume; (b) providing an organic polymeric binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof; (b-1) providing an organic polymer binder at a concentration of 150 g / L to 550 g / L; (c) preparing an additive selected from the group including plasticizers, antifoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, blowing agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof; (d) preparing a volatile organic solvent; (e) mixing the blended build material and additives to form a first premix; (f) mixing the dissolved organic polymer binder with a volatile organic solvent to form a second premix; (g) mixing the first premix with the second premix to form a substantially uniform, flowable slurry mixture that is printed as a precursor part of the functionally graded article.

[0120] The method preferably further comprises forming two or more substantially uniform, flowable slurry mixtures, each comprising a respective first premix and a respective second premix, and instantaneously mixing the two or more substantially uniform, flowable slurry mixtures in-situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

[0121] As described in the previous paragraphs, the organic polymer binder is debonded from the precursor part by either or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce a final part comprising said build material that selectively varies gradually in composition, configuration, including packing pattern, or any combination thereof, across the volume of the final part of the functionally graded article in one or more directions.

[0122] Although the method is depicted as a numbered sequence for clarity, the numbering does not necessarily dictate the order of the steps. It will be understood that some of these steps may be omitted, performed in parallel, or performed without the requirement of maintaining a strict order.

[0123] Referring to FIG. 8, a method for printing a functionally graded article (i.e., extrusion-based 3D printing) preferably includes the following steps.

[0124] (a) providing a slurry feedstock, (a-1) preparing a building material comprising a metal, a ceramic, or any combination thereof; (a-1-1) providing the build material, which may be porous, non-porous, or any combination thereof; (a-1-2) supplying the building material in an amount of 10% by volume to 90% by volume; (a-2) preparing an organic polymer binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof; (a-2-1) the preparing step including a step of providing an organic polymer binder at a concentration of 150 g / L to 550 g / L; (a-3) a preparing step of preparing an additive selected from the group including a plasticizer, an antifoaming agent, a dispersing agent, a sacrificial material, a dissipative material, a framework material, a water-soluble inorganic salt, a foaming agent, graphene, graphene oxide, a flame retardant, a toner, a release additive, a stabilizer, an antistatic agent, an impact modifier, a colorant, an antioxidant, and any combination thereof; (b) mixing the blended build material and additives to form a first premix; (c) mixing the dissolved organic polymer binder with a volatile organic solvent to form a second premix; (d) mixing the first premix with the second premix to form a substantially homogenous, flowable slurry mixture that is printed as a precursor component of the functionally graded article; (e) debinding the organic polymer binder from the precursor part by either or both of a pyrolysis process and a solvent debinding process; (f) subjecting the precursor part from which the organic polymer binder has been debonded to a sintering process to produce a final part comprising a build material that selectively has a gradually varying composition, configuration including packing pattern, or any combination thereof that varies across the volume of the final part of the functionally graded article in one or more directions.

[0125] The method preferably further comprises forming two or more substantially uniform, flowable slurry mixtures, each comprising a respective first premix and a respective second premix, and instantaneously mixing the two or more substantially uniform, flowable slurry mixtures in-situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

[0126] Although the method is depicted as a numbered sequence for clarity, the numbering does not necessarily dictate the order of the steps. It will be understood that some of these steps may be omitted, performed in parallel, or performed without the requirement of maintaining a strict order.

[0127] In a preferred embodiment of the present invention, the system used for extrusion-based 3D printing of functionally graded articles preferably includes one or more reservoirs, jetting adjustment means, a computing unit, a fluid driver, optionally a single static or dynamic mixer, and a print head. Figures 9A and 9B, 10, 11, 12, and 13 are exemplary illustrations of the system of the present invention.

[0128] In FIG. 9A, the system with a given print nozzle configuration is preferably placed on a flat surface or substrate (e.g., a heated plate) in a cavity of a heating chamber. A precursor part extruded from the print nozzle is deposited on the flat surface. The flat surface is a leveling platform (autogenous or mechanical) that operatively cooperates with the print nozzle to create the part in one embodiment of the invention. The leveling platform can be computationally controlled by the same or different computing unit as the computing unit for the print nozzle of the print head. The heating chamber and / or the heated plate are preferably optional.

[0129] FIG. 9B shows an arrangement for extrusion-based 3D printing to manufacture a functionally graded article, in which a slurry feedstock is contained in a container connected to a fluid driver, which delivers the slurry feedstock to a jetting adjustment means as controlled by a controller in a computing unit. Once the substantially uniform and flowable slurry mixture of the slurry feedstock is introduced to the print head, said feedstock is extruded through a print nozzle attached to the print head onto a flat surface to produce a green part of the functionally graded article. The print head preferably does not have a heater or the like. A heating plate is preferably optional. Hot air or room temperature ventilation may be provided on an optional basis.

[0130] One or more vessels, or containers, tanks, or vessels, are preferably configured to separately house the slurry feedstock and / or its components as described in the previous paragraph. The vessels are preferably hermetically sealed. The vessels may be made of metal, plastic, etc., or composites thereof, of various shapes and sizes.

[0131] In one embodiment, each vessel contains a build material, an organic polymer binder, an additive, and a volatile organic solvent in an individual and separate manner. For example, four separate vessels are provided, each adapted to store a build material, an organic polymer binder, an additive, and a volatile organic solvent. These four vessels are specially configured for in-situ mixing of the components of the slurry feedstock.

[0132] In another embodiment, the metal and ceramic of the build material are contained in different separate containers. As an example, the metal particles are stored in a first container and the ceramic particles are stored in a second container. The metal and ceramic of the build material can be stored in more separate containers, for example, depending on the properties (e.g., physical properties, chemical properties, rheological properties, etc.) of the particular metal or ceramic, the type of metal and / or ceramic (e.g., metal A, metal B, ceramic A, ceramic B, porous metal A, porous metal B, porous ceramic A, porous ceramic B, etc.), and the final properties required for the functionally graded article. In another embodiment of the invention, the build material can be mixed with additives forming a first premix and stored in one container, and the organic polymer binder can be dissolved with or in a volatile organic solvent forming a second premix and stored in another container. These two containers are configured to feed such a mixture (i.e., premixed build material and additives, and predissolved organic polymer binder in a volatile organic solvent) to said static or dynamic mixer.

[0133] In yet another embodiment, a first container is configured to store a slurry feedstock, which is a substantially homogenous and flowable slurry mixture containing one additive and a build material mixed with the organic polymer binder solution, and a second container is configured to store another additive mixed with the organic polymer binder solution. The first container and the second container are preferably arranged to vary the microporosity of the functionally graded article to obtain any desired or targeted packing pattern. In this regard, the another additive is a sacrificial material and / or a dissipative material. The above container arrangement may not be applicable to vary the microporosity.

[0134] The injection adjusting means is preferably mechanically connected to the vessel. The injection adjusting means is preferably configured to regulate the injection rate and amount of the slurry feedstock and / or its components stored in the vessel by controlling the position of a control piston provided therein. The injection adjusting means is preferably connected to and in communication with the controller of the computing unit.

[0135] The injection regulating means is preferably selected from the group including a solenoid valve, a mechanical pump, and combinations thereof.

[0136] The solenoid valve as used in the present invention, also called servo valve, refers to any device that can connect, more specifically communicate, in a controlled manner such that the pressure of the slurry feedstock and / or its components stored in a vessel located upstream of a static or dynamic mixer can be controlled by a user circuit located downstream. Such solenoid valves generally comprise two chambers and a slide valve. Depending on its position, the slide valve is controlled to connect one chamber to a high pressure supply circuit and the other chamber to a low pressure fluid return circuit. One of the chambers is also connected to the user circuit. It is noted that this type of solenoid valve device includes a pulsator in which the pressure source does not communicate directly with the user circuit, but is operatively connected thereto via an oscillating piston that is itself controlled by the solenoid valve.

[0137] Mechanical pump, or simply pump, as used herein, is a broad term and is any device capable of facilitating fluid flow, at least in the present invention, of facilitating the flow of a slurry feedstock. By way of example, pumps can include syringe pumps, peristaltic pumps, vacuum pumps, electric pumps, mechanical pumps, slurry pumps, centrifugal pumps, hydraulic pumps, and any combination thereof. Pumps and / or pump components suitable for use in some embodiments can be suitably obtained to ensure efficient and consistent pumping of the slurry.

[0138] A computing unit connected to the controller preferably refers to any system including a processor and a memory. In some embodiments, the computing unit may include a display. The computing unit is preferably configured to generate control signals for the jetting adjustment means, the static or dynamic mixer, and / or the print head. The control signal is a single signal or a set of multiple signals used to control the components connected thereto. The control signal can preferably control one or more properties (associated with the system), such as jetting speed, jetting volume, jetting time, deposition rate, print nozzle or print head positioning, shape of the functionally graded article, etc. The controller is preferably connected to a database comprising a predefined set of materials and rheological profiles used in the present invention. This database is used for the control signals to functionally influence the final part of the functionally graded article. For example, the control signal is adjusted according to the rheological profile of the build material to enable the jetting adjustment means to apply the correct jetting speed and / or jetting volume corresponding to said profile and the desired functionally graded article. The controller may include a hardware device including a memory and a processor integrated with a server. The memory is configured to store modules / units for executing instructions, and the processor is configured to execute said instructions, specifically to perform one or more processes described herein.

[0139] In some embodiments, the computing unit is a self-contained system. In some embodiments, the computing unit is not self-contained. The computing unit is a dedicated computer or dedicated computing device with computing power and / or storage memory (e.g., CPU, microprocessor, etc.), typically preferably executing operating software for operating the system of the present invention (e.g., jetting adjustment means, static or dynamic mixer and print head) to perform a predetermined printing procedure. The computing unit is integrated into the system of the present invention or is connected to the system in a dedicated manner to operate the system.

[0140] In an exemplary embodiment, the computing unit comprises a peer-to-peer module for receiving a request message to a peer-to-peer application, the request message including data or information and customization parameters of a desired product, i.e., a functionally graded article, to be manufactured by the system of the present invention.

[0141] A fluid drive is disposed adjacent to said vessel or said jet adjustment means. The fluid drive is preferably a pressure drive configured to provide or supply fluid pressure or pressurized fluid to or from a transfer mechanism to effect movement of the slurry feedstock and / or its components contained within the respective vessel, or a pressure drive of said jet adjustment means, to move the slurry feedstock and / or its components contained within the respective vessel to provide a pressurized slurry feedstock and / or pressurized components. Such term "fluid pressure" is intended to be broad enough to cover any suitable fluid pressure of this nature and to include vacuum.

[0142] In a preferred embodiment, the fluid drive of the present invention can be selected from the group including pneumatic drive, hydraulic drive, mechanical moving device, and any combination thereof. As used herein, said pneumatic drive preferably encompasses any type of equipment that is operated by passing compressed air. For example, pneumatic drive is a system operated by air or other gas under pressure, such as relatively low-cost yet efficient rotary piston air motors and portable high-pressure pneumatic barrels. Hydraulic drive is preferably a hydraulic drive incorporating a hydraulic motor, which may or may not have a separate reducer. Mechanical moving device can be used to transfer the slurry feedstock to the injection adjustment means. Fluid drive also includes any other motorized moving device that is suitably employed for the present invention.

[0143] The single static or dynamic mixer optionally used in the present invention is preferably configured to solely and instantaneously mix two or more substantially homogenous and flowable slurry mixtures in-situ to form one or a single substantially homogenous and flowable slurry mixture prior to transfer (transport) to the printhead.

[0144] A single static mixer or motionless mixer is essentially a mixer that does not include any internal moving mechanical parts. A static mixer is a device that includes one or more substantially stationary mixing elements, e.g., baffles such as blades, plates, vanes, etc., that mix flowing fluids, such as slurry feedstocks, and / or their components through a conduit to create flow division or splitting patterns to achieve mixing, e.g., helical mixing by radial circulation or exchange, in the flowing liquid. Static mixing elements are typically immobile within the conduit, but limited movement of the stationary elements relative to the conduit may occur unless they substantially contribute to the mixing of the flowing fluid. In a static mixer with multiple static mixing elements, these elements can be arranged in series and / or staggered relative to each other. Static mixers are preferably selected to generate a mixed flowing stream, i.e., a substantially uniform and flowable slurry mixture, over a short length of the mixer. Dynamic mixers, on the other hand, are the opposite of the static mixers and preferably include moving parts. The dynamic mixer can mix the slurry feedstock and its components together after or while they are being loaded therein. Other mixers of similar nature could be used in place of the aforementioned mixers, as those skilled in the art would be able to appropriately select.

[0145] A printhead with a print nozzle preferably includes a chamber for holding said substantially uniform and flowable slurry mixture immediately prior to printing or extruding onto a flat surface. Thus, in view of the slurry feedstock of the present invention, the printhead advantageously does not require a heater or the like. In one embodiment, the printhead includes a single printhead, a printbar, a carriage assembly or mounting block having multiple printheads with one or more print nozzles organized in a linear or non-linear array. The printhead is preferably operatively driven by its computational unit and configured to jet, extrude, distribute, deposit or generally eject said substantially uniform and flowable slurry mixture received directly from a fluid driver and / or received from a single static or dynamic mixer to generate a precursor part of said functionally graded article. The ejection of the substantially uniform and flowable slurry mixture is a non-contact dispensing process utilizing a printhead to form and project or extrude a continuous or non-continuous stream of slurry feedstock from a print nozzle onto a flat surface or substrate. A static or dynamic mixer can be connected to said printhead via a distribution unit which can be controlled by a separate computing unit or the same computing unit.

[0146] In one exemplary embodiment of the system of the present invention, as seen with reference to FIG. 10, the vessels (ie, vessel 1 and vessel 2) are connected to a fluid drive.

[0147] The jetting adjustment means is preferably disposed between the reservoir and a single static or dynamic mixer connected to the print head. The calculation unit preferably manages the jetting adjustment means, the static or dynamic mixer and the print head. The jetting adjustment means is preferably a mechanical pump.

[0148] Figure 11 is essentially the same as the configuration of Figure 10, except that in one exemplary embodiment of the system of the present invention, the distribution section is located between the static or dynamic mixer and the printhead. In this configuration, a computing section preferably manages the jetting adjustment means (i.e., the mechanical pump), the static or dynamic mixer, the distribution section, and the printhead.

[0149] In one exemplary embodiment of the system of the present invention, Figure 12 shows another arrangement using a solenoid valve as a jetting adjustment means. The solenoid valve is placed before the reservoir and connects with a fluid driver. A static or dynamic mixer is connected to the reservoir and to a distributor placed before the printhead. A computing unit preferably manages the solenoid valve, the static or dynamic mixer, the distributor and the printhead.

[0150] The present invention will be specifically described by the following examples, but it should be understood that the present invention is not limited to these examples.

[0151] The present invention allows a person, for example an engineer, to create FGM articles based on the transformation of metal A to metal B, metal A to ceramic A, or ceramic A to ceramic B by direct slurry writing technology (where A and B can be any metal or ceramic family). This versatile method of the present invention allows the material properties of the printed object to be changed in three dimensional directions (see Figures 3A and 3B) rather than in a single direction as disclosed in the prior art and / or conventional manufacturing methods. The present invention allows the full use or optimization by using or utilizing the superior properties of each material to form a unique metal / ceramic composite to maintain functionality under extreme conditions.

[0152] The extrusion-based printing of the present invention starts with the engineering design of a CAD model and target material profiles based on guidelines provided via a material database (encoded example profiles are shown in Figures 3A and 3B) to shape the unique properties of the FGM article. The CAD model is then processed via a pure program to generate Gcode (instructions to run the 3D printer) for the system of the present invention. This is followed by post-design processing software where the material profile is integrated with the generated Gcode. The post-processing tool allows the material mix ratio to be programmed into the Gcode so that the printer can change the mix composition during the printing process itself.

[0153] The unique 3D printer (which is the system of the present invention) may consist of two or more extruders, which allows mixing of two or more types of materials in the FGM print of the present invention. The slurry feedstock is provided in a container or tank with a pneumatic / hydraulic drive to provide pressure to move the slurry feedstock into a mechanical pump driven by a motor controlled by the printer controller. The slurry feedstock is precisely pumped into a static or dynamic mixer depending on the viscosity of the material to be printed. Because the feedstock is a slurry formulation, the mixing of two or more materials during printing can be easily scaled up and mixed in-situ during the printing process, as shown in FIG. 2, in contrast to existing additive methods or techniques where material changes can only be achieved in separate formulations (see FIG. 1).

[0154] The slurry mix print of the present invention relies on the deposition of a solvent-based binder to form a hardened print. Therefore, controlling the concentration of the organic polymer binder and the ratio between said binder and the binding particles (i.e., metal and / or ceramic powder) becomes a key step to ensure that the printed solution has enough static yield stress to maintain its shape after being extruded from the print nozzle, while still being able to be mixed using a static mixer (which refers to mixing of fluids without active moving parts) or a dynamic mixer (which includes a rotor that mixes fluids via a dynamic shear mechanism) to form a uniform slurry mixture during printing, as shown in Figure 2. Static or dynamic mixers have an effective viscosity working range.

[0155] To obtain a valid and homogenous mixture, the slurry mixture must be prepared such that both types of material feedstock have slight variations in viscosity change over a range of shear rates. Different types of powder sizes or shapes result in significant differences in terms of their rheological behavior. Rheological adjustments must be made within each material and in combinations of both mixtures across all the varying mixtures. Ideally, they should be within the range of about 30-90 vol.% for metals and / or ceramics, about 200-500 g / L and / or 10-70 vol.% for said organic polymer binders, and about 1-15 vol.% for additives. A valid mixture that can vary over a wide range of ratios between two materials is not obtained by simply mixing the two materials together. As an example, to obtain a flowable mixture suitable for a print rate of about 10-80 vol.%, feedstock material A may be required to be very viscous and material B very liquid in its material state. As both slurries are non-Newtonian in nature, similar shear or pumping rates may result in different volumetric flow rates, which may result in inaccuracies in the mix ratios programmed by the user. Therefore, in the present invention, the rheological profiles of the feed materials (i.e., the components of the slurry feedstock) and their mixtures must be achieved and mapped by experimental configuration. These rheological profiles are integrated with the design of the material profiles to form unique compensation factors that should be included during the post-processing of the pure Gcode to ensure that the feeding volumetric flow rates of both slurries are consistent so that a uniform mixing ratio is obtained. There is an achievable effective mixing ratio between the two materials, i.e., it is usually in the range of about 10-90%. This allows the generation of the formation of metal and ceramic mixtures, i.e., metal A and metal B, metal A (porous mixture) and metal A (non-porous mixture), ceramic A (porous) and ceramic A (non-porous) or ceramic A and ceramic B, depending on the needs and characteristics of the article that needs to be formed. The mixture of materials flowing through the mixer may be three or more types of materials and is not limited to those shown in any diagram.This configuration allows material A and material B to be mixed in precise ratios during the printing process.

[0156] An example configuration is shown below.

[0157] Material A (metal / ceramic A with liquid low concentration binder) and Material B (pure binder with additive premix). This prevents premature drying of the premixed slurry material during printing with only a single nozzle (to simplify preparation). The exact rheological behavior of the slurry can be tuned based on the printing conditions, i.e. temperature and humidity.

[0158] · The mixture of both materials, Material A (metal) and Material B (ceramic), can be precisely varied in three dimensions during printing via the printer controller software, making it possible to create a functionally graded material that varies across three dimensions as shown in Figures 3A and 3B. Note that this may be a mixture of two or more materials, varying in one or more directions, and printed in-situ.

[0159] · Material A (porous metal / ceramic mixture) is formed by the addition of a skeletal non-soluble material / foaming agent to Material A (concentrated mixture), where Material A can be selected from the group of metals and ceramics. This allows for the printing of unique structures such as shells that are filled with a solid and porous material (see Figure 4). The porosity gradient can be controlled to be not only linear or one-dimensional, but also parabolic gradients applied across 3D space as shown in Figure 4 (see Figures 5A and 5B).

[0160] Here, the definition of porous metal may refer to metal or ceramic / metal foam / ceramic foam. Porous structures can be classified as microporous (<100 μm) and macroporous (>100 μm). In this embodiment, macroporosity is obtained by controlling the packing structure through pure software (can be formed in various shapes such as honeycomb, adaptive cubes, triangles, stars, griloids, lines, concentric circles, Hilbert curves, lattice structures, etc.). The present invention can handle microporosity by adding foaming agents or sacrificial, dissipative, or scaffolding materials. This allows control of microporous and macroporous structures printed in a single solution by said in-situ mixing of porous and non-porous mixtures. Foaming agents can form random porous structures with minimal control over the porous shape and structure. Mixing by addition of sacrificial / fugitive / scaffolding materials provides precise control over pore size, density, and shape.

[0161] The following are non-limiting combinations of construction materials, including metals and ceramics. ·Metal-metal (i) Al-Cu (ii) Al-Ni (iii) Ni-Ti (iv) 316L-H13 (v) “Ti-6Al-4V”-304L (vi) Low carbon steel - high carbon steel (vii)304-304 porous structure Metal-ceramic (i) Al-SiC (ii) Al-Al2O3 (iii) Ni-ZrO2 (iv) Cu-SiC

[0162] ·Ceramic-Ceramic (i) SiC-SiC (different densities) (ii) Al2O3-Al2O3 (porous structure) (iii) Al2O3-SiC (iv) Al2O3-ZrO2

[0163] For FGM articles that include gradual material transitions (see metal-metal (i)-(v)), the base formulations for each individual material are illustratively shown in the table below. Such combination changes can be made between 0-100% for the gradient transition.

[0164] Table 3: Recommended final mixture composition [Table 3]

[0165] Table 4: Recommended porous composite mixtures [Table 4]

[0166] For the transition between low carbon steel and high carbon steel the following compositions can be used:

[0167] Table 5: Composition of the first mixture [Table 5]

[0168] Table 6: Composition of the second mixture [Table 6]

[0169] In the case of the 304-304 porous structure, the porosity of the structure is controlled by the size of the salt crystallization. The following can be used:

[0170] Table 7: Composition of the first mixture [Table 7]

[0171] Table 8: Composition of the second mixture [Table 8]

[0172] The following can be used to transition between clay and low carbon steel:

[0173] Table 9: Composition of the first mixture [Table 9]

[0174] Table 10: Composition of the second mixture [Table 10]

[0175] <Other embodiments / modes> The present invention further discloses a slurry feedstock for casting articles under low pressure and room temperature, a method for preparing the same, a method for casting articles, and a system therefor. Advantageously, the present invention simplifies conventional casting methods since the slurry feedstock used in conjunction with a reusable mold allows for casting of metal / ceramic articles without the need for high pressure or melting of metal. The present invention mainly focuses on a novel slurry-based feedstock prepared for metal / ceramic casting at room temperature, and the design and construction of a reusable mold. Since the feedstock is in slurry form, the slurry feedstock is fluid and mobile, allowing precise casting volume control into the mold with gravity or minimal pressure, further avoiding risky investments in high pressure injection systems. Furthermore, the present invention can be used and maintained in a very specific, compact, cost-effective, fast and simple manner without the use of complex and sophisticated processes, components or parts.

[0176] The term "article" as used herein refers to a manufactured article or semi-finished product of any shape that is produced from a slurry feedstock by mold casting.

[0177] As used herein, the term "slurry" refers to a solid-fluid mixture, including both solid-liquid and solid-gas mixtures. For convenience, the present invention will be discussed with respect to solid-liquid slurries as feed compositions in which the solids and liquids are in separate phases. Solid-liquid slurries also include solids and liquids that are introduced into the system of the present invention and that are fully or partially separated.

[0178] The term "feedstock" as used herein is defined as a raw material or mixture of raw materials having suitable properties to be fed into the present system capable of making an article, and is to be interpreted as components that are not yet mixed or that must be further mixed to produce a mixture suitable for use with the mold.

[0179] The term "premix" as used herein refers to ingredients that are mixed together and form one portion of the mixture that makes up the slurry mixture.

[0180] As used herein, the term "low pressure" refers to pressures below 2 MPa.

[0181] The term "room temperature" as used herein refers to a temperature range where no additional energy is consumed in the slurry feedstock or is close to the temperature. In one embodiment, the term refers to a temperature range of about 20°C to 30°C.

[0182] As used herein, the term "precursor part" or "green part" refers to an article or preform of an article in a pre-sintered state produced by the present invention for further processing by other manufacturing techniques.

[0183] As used herein, the term "brown part" refers to an article produced from a predecessor or green part that has been subjected to a pyrolysis process and / or a solvent debonding process to remove binders, sacrificial materials and / or fugitive materials that previously held the feedstock together. The brown part may be further heated to fully sinter the part or subjected to sintering to produce the final or finished part of the article.

[0184] In accordance with one preferred embodiment of the present invention, the slurry feedstock comprises a build material, an organic polymer binder, additives (which may be optional), and a volatile organic solvent.

[0185] The organic polymer binder is preferably dissolved in a volatile organic solvent, thus creating an organic polymer binder solution. Additives are preferably added to the build material to obtain predetermined rheological behavior and print properties. The slurry feedstock can essentially be formed by blending said organic polymer binder solution with said build material mixed with additives. The resulting slurry feedstock can be introduced into a reusable mold and dried by phase inversion at room temperature without external heat supply means.

[0186] The build material of the present invention preferably refers to the powder used to form the slurry feedstock and from which the article is built in the system for casting of the present invention. The powder, or powders referred to as particulate materials or particles, have various mesh sizes. In one embodiment, the build material has a particle size of about 300 μm or less, preferably less than about 200 μm. The build material is preferably a layer forming material for use in the system for casting of the present invention. The build material may also be in various forms such as granular powder, fibrous powder, and scaly powder. In a preferred embodiment, the build material is used in an amount of about 10% to about 90% by volume, more preferably about 30% to about 90% by volume.

[0187] The building material preferably comprises a metal, a ceramic, or any combination thereof. In one embodiment of the present invention, the building material may be porous, non-porous, or any combination thereof. For example, porous metal refers to metal particles having significant porosity, e.g., porosity greater than about 0.5 cc / g. The building material may have pores less than 100 μm (microporous) and / or greater than 100 μm (mesoporous). On the other hand, non-porous metal refers to metal particles having little or no porosity, e.g., porosity less than about 0.05 cc / g. Porous ceramics preferably have porosity with controllable porosity and good mechanical properties. The term "porosity" as used herein refers to the volume fraction of void space in a porous article, e.g., its porous building material.

[0188] The porous metals and / or porous ceramics used in the present invention are preferably microporous and can be produced, for example, by direct foaming using suitable foaming agents, sacrificial materials, dissipative materials, skeletal materials, etc. Porosity can also be controlled by the size of salt crystallizations.

[0189] In a preferred embodiment of the present invention, the build material may include only metal (porous and / or non-porous) or ceramic (porous and / or non-porous). The build material may also include combinations of metal and ceramic in a predetermined mix ratio or volume percentage to suitably meet the desired properties of the build material for the article. Examples of such combinations include metal and ceramic; porous metal and ceramic; metal and porous ceramic; porous metal, non-porous metal and ceramic; metal, porous ceramic and non-porous ceramic; porous metal, non-porous metal, porous ceramic and non-porous ceramic, etc. Various other combinations are contemplated (e.g., first metal, second metal, first ceramic, second ceramic, etc.).

[0190] The metals used in the present invention are preferably selected from the group comprising ferrous metals, non-ferrous metals, ferrous metal alloys, and non-ferrous metal alloys.

[0191] The ferrous metal is selected from steel, stainless steel, mild steel, cast iron, malleable iron, ductile cast iron, and the like. The ferrous metal preferably includes iron, iron-chromium alloys, iron-chromium-nickel alloys, iron-chromium-zinc alloys, iron-chromium-aluminum alloys, iron-chromium-magnesium alloys, iron-chromium-lead alloys, iron-aluminum alloys, iron-zinc alloys, stainless steel, iron-nickel alloys, and combinations thereof. Preferred examples of steel and / or stainless steel materials include AISI 304, AISI 304L, AISI 316, AISI 316L, AISI 430, AISI 630 (17-4PH), and AISI 631 (17-7PH). Other steel materials such as A2-A5, D2, H13, M2, and 4140 can also be used in the present invention.

[0192] The non-ferrous metals are selected from aluminum, aluminum alloys, magnesium, magnesium alloys, zinc, zinc alloys, cadmium, chromium (III), copper, copper (II) cadmium, lead, cobalt, cobalt chromium, cobalt chromium molybdenum, nickel, nickel alloys, molybdenum, titanium, tantalum, niobium, silver and gold. Preferred examples of aluminum and / or aluminum alloys include AlSi10Mg, AlSi7Mg, ADC12 and AlMg5Mn. Preferred examples of nickel alloys include alloy 706, alloy 718, alloy 625, alloy 725 and invar types such as FeNi36 or 64FeNi, or Hastelloy X, Hastelloy C and Kovar.

[0193] The ceramics used in the present invention are preferably selected from the group comprising silicate ceramics, oxide ceramics, non-oxide ceramics, bioceramics, and any combination thereof.

[0194] The silicate ceramic preferably includes, but is not limited to, clay, cordierite ceramic, steatite, stoneware, earthenware, porcelain, kaolin, quartz, silicate, camot, bentonite, mullite, and any combination thereof.

[0195] The oxide ceramics preferably include, but are not limited to, alumina, zirconia including zirconia stabilized in yttria oxide (YO), beryllium oxide, yttrium oxide, titanium oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, uranium oxide (UO), plutonium dioxide (PuO), barium yttrium copper oxide, spinel, magnetoplumbite, perovskite, tialite, and any combination thereof.

[0196] Non-oxide ceramics preferably include, but are not limited to, carbide ceramics such as titanium carbide, boron carbide, tungsten carbide, silicon carbide, nitride ceramics such as silicon nitride, boron nitride, aluminum nitride, aluminum oxynitride, nitride ceramics including SiAION (ceramics based on the elements silicon (Si), aluminum (Al), oxygen (O) and nitrogen (N)), and any combination thereof.

[0197] The bioceramic is preferably a calcium phosphate ceramic, including, but not limited to, hydroxyapatite (HAP), tricalcium phosphate (TCP), amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), tetracalcium phosphate monoxide (TetCp), biphasic calcium phosphate (BCP), and any combination thereof.

[0198] The build materials of the present invention may include other sinterable materials that do not crack, sag, or delaminate, such as glass powder, acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyether ether ketone (PEEK).

[0199] The organic polymer binders used in the present invention preferably have at least two pyrolysis temperatures. In pyrolysis, decomposition products (i.e. articles) that can act as reducing agents are formed when the organic polymer binder is heated at these temperatures. The organic polymer binder is preferably selected so as not to inhibit the reaction between the powders, i.e. metal and / or ceramic particles. The organic polymer binder preferably decomposes or evaporates at temperatures below its corresponding pyrolysis temperature.

[0200] The organic polymer binder is preferably selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof. The organic polymer binder is preferably used at a concentration of about 50 g / L to about 550 g / L, more preferably about 100 g / L to about 500 g / L. In various embodiments of the present invention, the number average molecular weight of the organic polymer binder is about 150,000 or less, more preferably about 100,000 or less.

[0201] The cellulose ester is preferably selected from the group comprising cellulose acetate, cellulose acetate phthalate, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose butyrate, cellulose tributyrate, cellulose acetate propionate, cellulose propionate, cellulose tripropionate, cellulose nitrate, cellulose acetate propionate, carboxymethyl cellulose acetate, carboxymethyl cellulose acetate propionate, carboxymethyl cellulose acetate butyrate, cellulose acetate butyrate succinate, cellulose propionate butyrate, and mixtures thereof.

[0202] Cellulose ester derivatives can be prepared by esterification of cellulose.Preferred cellulose ester derivatives include cellulose acetate, butyrate, benzoate, phthalate and anthranilic acid esters, preferably cellulose acetate phthalate (CAP), cellulose acetate butyrate (CAB), cellulose acetate trimellitate (CAT), hydroxypropyl methylcellulose phthalate (HPMCP), succinoyl cellulose, cellulose fluorate, cellulose carbanilate and mixtures thereof.

[0203] The cellulose ether is preferably selected from the group comprising methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxyethyl cellulose, methyl ethyl hydroxyethyl cellulose, hydrophobically modified ethyl hydroxyethyl cellulose, hydrophobically modified hydroxyethyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose, carboxyalkyl hydroxyalkyl cellulose, and mixtures thereof.

[0204] The cellulose ether derivatives can be prepared by carboxymethylation, carboxyethylation and carboxypropylation. Examples of preferred cellulose ether derivatives include, but are not limited to, nanocellulose, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (NaCMC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC), hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), ethylcellulose (EC), tritylcellulose, etc.

[0205] Some organic polymer binders may use cationic cellulose derivatives. Some of the organic polymer binders may include alginates, starches, polysaccharides such as chitin and chitosan, agarose, hyaluronic acid, and derivatives or copolymers thereof (e.g., graft copolymers, block copolymers, random copolymers), or mixtures thereof.

[0206] The additives used in the present invention may be added to the build material and its organic polymer binder to achieve any desired properties, such as desired physical, mechanical, and thermal properties in the slurry feedstock. In a preferred embodiment of the present invention, the additives are selected from the group including plasticizers, defoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water-soluble inorganic salts, foaming agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof. The additives are preferably used in an amount of about 1% to about 15% by volume. It is understood that the amount of additives may vary outside of said ranges depending on the specific type of additive selected in the present invention.

[0207] By plasticizer, it is preferred to mean a substance added to the slurry feedstock to improve workability, flexibility and plasticity.Preferably, the plasticizer comprises an additive selected from the group comprising dibutyl phthalate, diaryl phthalate, diethyl phthalate, dimethyl phthalate, dihexyl phthalate, di-2-methoxyethyl phthalate, triphenyl phthalate, (dipropylene glycol) butyl ether, dibutyl tartrate, diethylene glycol monoricinoleate and other phthalates, cetyl alcohol, stearyl alcohol, cetostearyl alcohol, natural or synthetic waxes selected from the group consisting of beeswax, candelilla wax, shellac wax, carnauba wax, petroleum wax, or mixtures thereof, glycerol, triethyl citrate, acetyl triethyl citrate, ethyl o-benzoyl benzoate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, N-ethyl toluene sulfonamide, o-cresyl p-toluene sulfonate, triethyl phosphate, triphenyl phosphate, and any combination thereof.

[0208] The defoamer is a material that eliminates bubbles, preferably by reducing the surface tension of the slurry feedstock. The defoamer serves to change the surface properties of metals and ceramics and reduce the interfacial tension of volatile organic solvents to eliminate foam. The defoamer is preferably selected from the group including polyethylene glycol, polypropylene glycol copolymer, alkyl polyacrylate, polydimethylsiloxane (silicone oil), ethylene bisstearamide (EBS), paraffin wax, ester wax, fatty alcohol wax, white oil or vegetable oil, wax with long chain fatty alcohol, fatty acid soap, ester, polyether modified polysilane and trialkane / alkene phosphate and mixtures thereof.

[0209] The dispersant is preferably a compound selected from the group consisting of a silicate compound, sodium polycarbonate, and an alcohol.The dispersant is preferably a compound selected from the group consisting of a silicate compound, sodium polycarbonate, and an alcohol.

[0210] The sacrificial material is preferably a substance that, if present in the green or brown part prior to sintering, is not present, at least in the same form and in any significant amount, in the fully sintered body (i.e., the final part) formed upon sintering of the brown part into the final article or part. In one embodiment, the sacrificial material forms a layer on the green or brown part and is later removed to leave a void. The sacrificial material may comprise aluminum orthophosphate, which upon elevated temperature during the sintering process first forms a liquid phase within the green or brown part and then vaporizes or decomposes as one or more gaseous by-products, leaving the green or brown part. The sacrificial material preferably comprises paraffin wax.

[0211] The dissipative material is preferably a material that can act as a mold for casting the ceramic and / or metal parts into the three-dimensional shape of the functionally graded article and can then be removed from the ceramic and / or metal parts by dissolving, melting and / or evaporating without damaging the ceramic and / or metal cast parts. The dissipative material used in the present invention may be a rubber or plastic material selected to achieve desired properties such as thermal expansion and / or dissipative behavior (relative to the ceramic or metal core material).

[0212] In one embodiment, the sacrificial material, the dissipative material, or a combination thereof is removed from a predecessor part or a predecessor part from which the polymer binder has been debonded by pyrolysis, solvent debonding, or any combination thereof (i.e., brown part). The pyrolysis can be preferably selected from the group including heating, thermal debonding, densification / sintering, partial or complete melting of the sacrificial material and / or dissipative material other than the build material, i.e., metal and / or ceramic particles. The solvent debonding may include immersing the predecessor part, brown part, and / or final part in a solvent that dissolves the sacrificial material and / or dissipative material. The distortion can be better controlled and the debonding time can be significantly reduced. The solvents include, but are not limited to, alternative solvents such as n-hexane, heptane, paint thinner, acetone, methyl ethyl ketone, carbon tetrachloride, trichloroethylene, methylene chloride, and supercritical carbon dioxide, as well as water.

[0213] The scaffolding material is preferably a buttress material to provide mechanical integrity to the slurry feedstock. The scaffolding material may be selected from the group including gel-like materials such as chitosan, fibrin, modified alginates, tough materials such as polycaprolactone and other plastics, and slurries containing ceramic and other powders, hydroxyapatite, or tricalcium phosphate. The scaffolding material may also include polycaprolactone, polylactic acid, polyglycolic acid, and poly(lactide-co-glycolide).

[0214] The water-soluble inorganic salts used in the present invention are preferably selected from the group comprising nitrates, borates, chlorates, perchlorates, sulfates, halide salts, sodium carbonate, potassium carbonate, silicates, phosphates, salts of Group I elements, ammonium salts and combinations thereof. In one embodiment, the water-soluble inorganic salt comprises a rare earth metal chloride.

[0215] Foaming agent or blowing agent refers to a component or combination of components capable of forming a foam, preferably generally a cellular foam, preferably in the slurry feedstock, particularly the metal and / or ceramic of the construction material. Foaming agents may be solid, liquid, or supercritical materials.

[0216] In a preferred embodiment of the invention, the blowing agent is a thermally decomposable agent that is liquid or solid at room temperature, has a decomposition temperature below the melting temperature of the build material, and when heated above its decomposition temperature, decomposes while generating a gas such as nitrogen, carbon dioxide or ammonia. The blowing agent may be selected from the group including azodicarbonamide and / or metal salts thereof, hydrazodicarbonamide, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, calcium azide, trihydrazino-sym-triazine, p-oxybisbenzenesulfonylhydrazide, dinitrosopentamethylenetetramine, azobisisobutyrodinitrile, toluenesulfonylhydrazide, p-toluenesulfonylhydrazide, benzenesulfonylhydrazide, bisbenzenesulfonylhydrazide, p,p'-oxybis(benzenesulfonylhydrazide), azobisisobutyronitrile, barium azodicarboxylate, and combinations thereof. The polysaccharide foaming agent preferably includes arrowroot flour, tapioca starch, potato starch, wheat, rice, and corn flour. The amount of foaming agent can be determined according to the desired expansion coefficient.

[0217] The graphene used as an additive in the present invention is preferably a polycyclic aromatic compound formed by covalently bonding multiple carbon atoms. The covalently bonded carbon atoms form a 6-membered carbon ring as a repeating unit, and may further include a 5-membered carbon ring and / or a 7-membered carbon ring. In the present invention, graphene is not limited to single-layer graphene, but also includes, for example, multi-graphene having up to 10 single-layer graphene layers. Graphene preferably includes pure or natural graphene in addition to modified graphene such as graphene oxide or amide-modified graphene.

[0218] Graphene oxide, also known as "graphitic acid" and "graphite oxide", may include, but is not limited to, structures in which oxygen-containing functional groups, such as carboxyl, hydroxyl, or epoxy groups, are attached to the graphene in varying proportions, and may be obtained by treating graphite with a strong oxidizing agent. In one embodiment of the present invention, the graphene oxide includes nanocomposites comprising graphene oxide. Graphene oxide also includes reduced graphene oxide, i.e., graphene oxide in reduced form, e.g., graphene oxide that has been subjected to a reduction treatment to be partially or substantially reduced. Reduced graphene oxide also refers to graphene oxide in which the percentage of oxygen has been reduced by reduction treatment.

[0219] Other additives such as flame retardants, toners, mold release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and mold release agents may be used in the present invention.

[0220] The volatile organic solvent is chemically inert to the build material, but is preferably evaporated or released by the system of the present invention during or after casting. The volatile organic solvent is necessary to completely dissolve the components of the slurry feedstock other than the build material (e.g., organic polymeric binder), and also functions as a wetting agent. It is also desirable to use a volatile organic solvent that promotes variability (changes) of the build material (i.e., metal and ceramic) in the article's composition, structure including packing pattern, or any combination thereof, has a relatively high flash point, and has a relatively low odor. The volatile organic solvent is preferably a solvent that has a low vapor pressure, preferably greater than about 0.133 mbar or 13.3 Pa (0.1 mmHg) at about 20°C.

[0221] The volatile organic solvent is preferably used in an amount of about 1% to about 50% by volume. In one embodiment of the present invention, an appropriate amount of the volatile organic solvent should be used in the organic polymer binder, taking into consideration the preferred or desired concentration of the resulting solution as the second premix, which is the organic polymer binder solution.

[0222] The volatile organic solvent is preferably selected from the group comprising ketones including acetone, butanone, methyl ethyl ketone, methyl amyl ketone, methyl isobutyl ketone and cyclohexanone, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols including methanol, ethanol, propanol, isopropyl alcohol and butanol, methyl formate, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, ethyl acetate, isopropyl acetate, ethyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, nitromethane, acetonitrile, methylcyclohexane, n-heptane, n-hexane, cyclohexane, dipropylene glycol n-butyl ether, and mixtures thereof.

[0223] In various embodiments of the present invention, the build material mixed with the additive preferably forms a first premix, and the organic polymer binder dissolved with or in a volatile organic solvent (i.e., the organic polymer binder solution) forms a second premix. The first premix and the second premix are preferably mixed to form a substantially homogeneous and flowable slurry mixture, which is then subjected to casting in a cavity of a mold. The mold is then substantially immersed in a coagulation bath for producing a precursor part of the article by phase inversion, whereby the volatile organic solvent is extracted from the article to control or manipulate, as minimally as possible, the porosity or pores formed in the resulting article (i.e., the precursor part). The second premix is ​​preferably in an amount of about 10% to about 90% by volume, more preferably about 10% to about 70% by volume.

[0224] The mixing preferably forms or produces a substantially homogeneous and flowable slurry mixture that is subjected to the system to manufacture the precursor part of the article. The substantially homogeneous and flowable slurry mixture of the present invention can refer to a composition that is homogeneously mixed in the same state with substantially one morphological phase, such that at least two random samples of the composition have roughly or substantially the same amount, concentration and distribution of the components (e.g., build material, organic polymer binder, additives, and / or volatile organic solvent) therein. The substantially homogeneous and flowable slurry mixture of the present invention is also meant to encompass compositions having components (e.g., build material, organic polymer binder, additives, and / or volatile organic solvent) that are flowable under gravity and / or can be pumped (pumped). The substantially homogeneous and flowable slurry mixture also exhibits the ability of the composition to be transported from a containment vessel, such as a container, by gravity or by conventional mechanical, hydraulic, or pneumatic pumping means.

[0225] In one preferred embodiment, the substantially uniform and flowable slurry mixture comprises two or more substantially uniform and flowable slurry mixtures. As shown in FIG. 20 and FIG. 21, the two or more substantially uniform and flowable slurry mixtures are mixed in-situ instantaneously with or without a static or dynamic mixer to form one substantially uniform and flowable slurry mixture. The two or more substantially uniform and flowable slurry mixtures preferably comprise two substantially uniform and flowable slurry mixtures, each comprising a first premix and a second premix. For example, there are two substantially uniform and flowable slurry mixtures, i.e., a first substantially uniform and flowable slurry mixture and a second substantially uniform and flowable slurry mixture. The first substantially uniform and flowable slurry mixture comprises a first premix comprising a metal, which is a construction material, preferably mixed with a dispersant, which is an additive, and a second premix comprising a cellulose ester, which is an organic polymer binder, dissolved in acetone, which is a volatile organic solvent. The second substantially homogenous and flowable slurry mixture preferably comprises a first premix comprising a ceramic build material mixed with a foaming agent additive, and a second premix comprising the organic polymer binder cellulose ether dissolved in a volatile organic solvent butanone. The resulting first and second substantially homogenous and flowable slurry mixtures are mixed in the single static or dynamic mixer to form a single substantially homogenous and flowable slurry mixture prior to injection into the mold.

[0226] The term "in-situ" will be understood to mean the location where mixing occurs or provides for mixing, or on-site mixing. Thus, to form a slurry feedstock at the mixing site, the build material, organic polymer binder, additives and / or volatile organic solvents are generally co-injected (co-delivered) or otherwise provided together in a single static or dynamic mixer (destination site) and mixed or assembled at the co-injection site within the single static or dynamic mixer.

[0227] It will also be understood that the term "instantaneous" or "instantaneous" refers to the time required to mix the build material, organic polymer binder, additives, volatile organic solvent, build material mixed with additives, and / or said organic polymer binder dissolved with or in a volatile organic solvent (i.e., organic polymer binder solution) to prepare the slurry feedstock in the single static or dynamic mixer. In the present invention, such instantaneous mixing may occur in a time period of one to several seconds. Mixing on the order of several seconds can be considered very rapid or instantaneous when compared to the total time of the process.

[0228] It should be further understood that the term "single static or dynamic mixer" as used herein refers to a single unit of static or dynamic mixer, and not multiple non-operably linked random mixers, as in the prior art.

[0229] In various embodiments of the present invention, the organic polymer binder is debonded from the prior component in a pyrolysis process, preferably based on the pyrolysis temperature, a solvent debonding process, or a combination thereof. The pyrolysis process can be selected from the group including heating the component other than the build material, i.e., other than the metal and / or ceramic particles, thermal debonding, densification / sintering, partial or complete melting, and / or potentially post-densification annealing, to relieve or further increase residual stresses in the prior component. In some embodiments, the pyrolysis process of heating can be effected at room temperature or at lower temperatures and shorter times than normal heat treatment times and temperatures, e.g., from about 60° C. to about 200° C., from about 10 minutes to about 10 hours.

[0230] Solvent debonding of the precursor part may include contacting the precursor part with a solvent to extract the soluble binder (along with additives, if any) from the body. Solvents suitable for solvent debonding according to the present invention preferably include acetone, methyl ethyl ketone, heptane, carbon tetrachloride, trichloroethylene, methylene chloride, and alternative solvents such as supercritical carbon dioxide, and water.

[0231] The pyrolysis process and / or the solvent debinding process of the precursor part may be followed by a sintering process to produce a final part of the article.

[0232] According to one preferred embodiment of the invention, in order to obtain said precursor part (or green part), the following may be practically used:

[0233] Table 11: Composition of the first mixture [Table 11]

[0234] Table 12: Composition of the second mixture [Table 12]

[0235] Referring to FIG. 22, a method of preparing a slurry feedstock for use in casting an article preferably includes the following steps. (a) preparing a build material comprising a metal, a ceramic, or any combination thereof; (a-1) providing a build material, which may be porous, non-porous, or any combination thereof; (a-2) supplying the building material in an amount of 10% by volume to 90% by volume; (b) providing an organic polymeric binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof; (b-2) providing an organic polymer binder at a concentration of 50 g / L to 550 g / L; (c) preparing an additive selected from the group including plasticizers, antifoamers, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, blowing agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof; (d) preparing a volatile organic solvent; (e) mixing the blended build material and additives to form a first premix; (f) mixing the dissolved organic polymer binder with a volatile organic solvent to form a second premix; (g) mixing the first premix with the second premix to form a substantially homogenous, flowable slurry mixture for casting in a mold cavity substantially immersed in a coagulation bath for producing a precursor part of said article by phase inversion, whereby the volatile organic solvent is extracted from the article to control, as minimally as possible, the porosity or pores formed in the resulting article (i.e., the precursor part).

[0236] The method preferably further comprises forming two or more substantially uniform, flowable slurry mixtures, each comprising a respective first premix and a respective second premix, and instantaneously mixing the two or more substantially uniform, flowable slurry mixtures in-situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

[0237] As described in the previous paragraphs, the organic polymer binder is debonded from the precursor part by either or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce a final part of the article comprising a build material that selectively varies in composition, configuration, including packing pattern, or any combination thereof, gradually across the volume of the final part in one or more directions.

[0238] Although the method is depicted as a numbered sequence for clarity, the numbering does not necessarily dictate the order of the steps. It will be understood that some of these steps may be omitted, performed in parallel, or performed without the requirement of maintaining a strict order.

[0239] 23 and 24, a method of casting an article preferably includes the following steps. (a) providing a slurry feedstock, (a-1) preparing a building material comprising a metal, a ceramic, or any combination thereof; (a-1-3) providing the build material, which may be porous, non-porous, or any combination thereof; (a-1-4) supplying the building material in an amount of 10% by volume to 90% by volume; (a-2) preparing an organic polymer binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof; (a-2-2) the preparing step including a step of providing an organic polymer binder at a concentration of 50 g / L to 550 g / L; (a-3) preparing an additive selected from the group including a plasticizer, an antifoaming agent, a dispersant, a sacrificial material, a dissipative material, a framework material, a water-soluble inorganic salt, a foaming agent, graphene, graphene oxide, a flame retardant, a toner, a release additive, a stabilizer, an antistatic agent, an impact modifier, a colorant, an antioxidant, and any combination thereof; (a-4) the supplying step including a preparing step of preparing a volatile organic solvent; (b) mixing the blended build material and additives to form a first premix;

[0240] (c) mixing the dissolved organic polymer binder with a volatile organic solvent to form a second premix; (d) mixing the first premix with the second premix to form a substantially uniform, flowable slurry mixture; (e) subjecting the substantially homogeneous and flowable slurry mixture to casting in a mold; (f) substantially immersing the mold having the cavity filled with the substantially uniform, flowable slurry mixture in a coagulation bath to extract the volatile organic solvent by phase inversion to produce a precursor part of said article; (g) debinding the organic polymer binder from the precursor part by either or both of a pyrolysis process and a solvent debinding process; (h) subjecting the precursor part from which the organic polymer binder has been debound or removed (i.e., the brown part) to a sintering process to produce a final part of the article.

[0241] The method preferably further comprises forming two or more substantially uniform, flowable slurry mixtures, each comprising a respective first premix and a respective second premix, and instantaneously mixing the two or more substantially uniform, flowable slurry mixtures in-situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

[0242] Although the method is depicted as a numbered sequence for clarity, the numbering does not necessarily dictate the order of the steps. It will be understood that some of these steps may be omitted, performed in parallel, or performed without the requirement of maintaining a strict order.

[0243] In a preferred embodiment of the invention, the system used to cast the article preferably comprises one or more vessels, (reusable) molds, coagulation baths, debinding means, and optionally a single static or dynamic mixer.

[0244] One or more vessels, or containers, tanks, or vessels, are preferably configured to separately house the slurry feedstock and / or its components as described in the previous paragraph. The vessels are preferably hermetically sealed. The vessels may be made of metal, plastic, etc., or composites thereof, of various shapes and sizes.

[0245] In one embodiment, each vessel contains a build material, an organic polymer binder, an additive, and a volatile organic solvent in an individual and separate manner. For example, four separate vessels are provided, each adapted to store a build material, an organic polymer binder, an additive, and a volatile organic solvent. These four vessels are specially configured for in-situ mixing of the components of the slurry feedstock.

[0246] In another embodiment, the metal and ceramic of the building material are contained in different separate containers. As an example, the metal particles are stored in a first container and the ceramic particles are stored in a second container. The metal and ceramic of the building material can be further stored in a number of separate containers depending, for example, on the properties (e.g., physical properties, chemical properties, rheological properties, etc.) of the particular metal or ceramic, the type of metal and / or ceramic (e.g., metal A, metal B, ceramic A, ceramic B, porous metal A, porous metal B, porous ceramic A, porous ceramic B, etc.), and the required final properties of the article. In another embodiment of the invention, the building material can be mixed with additives forming a first premix and stored in one container, and the organic polymer binder can be dissolved with or in a volatile organic solvent forming a second premix and stored in another container. These two containers are configured to feed such a mixture (i.e., premixed building material and additives, and predissolved organic polymer binder in a volatile organic solvent) to said static or dynamic mixer.

[0247] In yet another embodiment, a first container is configured to store a slurry co-ingredients, which is a substantially homogenous and flowable slurry mixture containing one additive and a build material mixed with the organic polymer binder solution, and a second container is configured to store another additive mixed with the organic polymer binder solution. The first container and the second container are preferably arranged to vary the microporosity of the article to obtain any desired or targeted packing pattern. In this regard, the another additive is a sacrificial material and / or a dissipative material. The above container arrangement may not be applicable to vary the microporosity.

[0248] The reusable mold is essentially configured to mold the substantially homogenous and flowable slurry mixture received or dispensed from one or more containers in its cavity. The cavity is preferably used to obtain an article having a desired shape. The cavity is preferably formed concentrically, internally, and centrally within the body of the mold. In one embodiment, the mold has an effectively continuous mold wall or casting surface of any desired shape surrounding the cavity. The cavity may be of any shape, including regular or irregular polygonal shapes, such as a bell shape, a pyramidal trunk shape, and a truncated sphere shape with two bases.

[0249] Mold walls are often rectangular or square in shape, but may be circular or any other symmetrical or asymmetrical shape to produce articles having a corresponding cross-sectional shape. If desired, the enclosing mold wall may be adjustable in length and / or shape, for example, by providing an end wall that is slidable between a pair of parallel side walls to vary the cross-sectional area and shape of the cavity defined by the wall. In such a configuration, the end wall may not be integral with the side wall portions, but the walls fit closely together such that the combined mold wall consisting of the end wall and side wall portions is effectively continuous and avoids molten metal leakage.

[0250] In a preferred embodiment, the mold comprises a first part in which a cavity is recessed or formed. The first part of the mold may be defined by two sub-parts having faces facing each other and joining along a central parting plane to form a single piece of the first part. The two sub-parts preferably include a female sub-part and a male sub-part that can be seamlessly joined or mated and held in place with or without locking means such as pins and latches. The two sub-parts of the first part can be disassembled or removable to remove or dismantle the resulting pre-part from the empty cavity.

[0251] The first part of the mold is preferably made of or is made of a material selected from silicone, ceramic, concrete, thermoplastics, UV curable resins including high density polyethylene, medium density polyethylene, low density polyethylene, crosslinked polyethylene, polytetrafluoroethylene, polyethylene terephthalate, and polypropylene, polycarbonate, polylactide, epoxy resin, acrylonitrile butadiene, styrene, fiberglass, nylon, and any combination thereof. Other materials that are non-soluble in ketone and alcohol solvents can also be used in the present invention. In one embodiment, the first part of the mold is obtained, manufactured, or prepared by additive manufacturing or three-dimensional (3D) printing.

[0252] The first part of the mold may be permeable or non-permeable. When permeable, the first part may have a peripheral wall with a permeable wall portion. Although the term permeable is used herein, the entire peripheral wall of the first part is not necessarily permeable, but instead, only the portion where gas flow is desired. The permeable wall portion can be made of ceramic, silicone (depending on the material properties), or microstructures printed on the mold, which are engineering design structures. The permeable first part is essentially configured to allow a phase change to occur between the non-solvent particulates in the coagulation bath and the solvent in the slurry mixture, forming controllable pores in the article during the drying process.

[0253] The mold of the present invention may further include a second part. The second part, preferably a single part, is configured to removably encase the first part. The second part may be a tubular or elongated outer cylinder that is slidably engageable with the outer wall of the first part such that the first part can be snugly inserted therein. The second part may encase or cover a portion or substantially the entirety of the first part. The second part may or may not be of a liquid-resistant construction relative to the first part. In one embodiment, the second part of the mold may allow liquid, e.g., from a coagulation bath, to enter and contact the substantially homogenous and flowable slurry mixture dispensed into the first part and / or its cavity to initiate phase inversion.

[0254] The second part may be made of the same material as the first part. In one embodiment, the second part is obtained, manufactured or prepared by additive manufacturing or 3D printing. To increase, improve or improve the strength and structural integrity of the second part, solid silicone can be applied to the second part of the mold.

[0255] The second part of the mold may be permeable or non-permeable. If permeable, the second part may have a peripheral wall with a permeable wall. Although the term permeable is used herein, the entire peripheral wall of the second part is not necessarily permeable, but instead only the portion where gas flow is desired. The permeable wall portion can be made of ceramic, silicone (depending on the material properties), or microstructures printed on the mold, which are engineering design structures. The permeable second part is essentially configured to allow a phase change to occur between the non-solvent particulates in the coagulation bath and the solvent in the slurry mixture, forming controllable pores in the article during the drying process.

[0256] In a preferred embodiment of the present invention, the first part of the mold can be prepared by a silicone mold making process in which the physical article to be cast is used to form a negative silicone mold. The silicone mold is cast and subjected to a cleaning process using a permeable silicone formulation (i.e., a mixture of room temperature vulcanizing (RTV) silicone / platinum cured silicone and fine salt whose particle size is within 5-10 μm) to form a permeable silicone mold with pore size of 5-10 μm. This allows phase inversion between the casting slurry mixture and the non-solvent. The second part of the mold is an external permeable mold, which can be coated with a solid silicone wall to increase the rigidity of the mold and extend its reusability.

[0257] In another preferred embodiment of the present invention, the mold can be made by 3D printing process by fuse deposition method (FDM) using various thermoplastic resins such as thermoplastic resins such as HDPE, LDPE, PETG, PP, PC, or thermoplastic resins that are insoluble in ketone & alcohol solvents, stereolithography (SLA) using UV-based resins that resist ketone groups, or direct ink writing method using transparent silicone formulations to form transparent molds. In the case of FDM and SLA methods, transparent molds can be obtained by embedding microchannels of the mold design and realizing them using 3D printing.

[0258] According to one embodiment of the present invention, in the manufacture of the article according to the invention, it is cast into one integral part from at least two different substantially homogeneous and flowable slurry mixtures of different material components (e.g. material A and material B in Fig. 2 and Fig. 3). The at least two different substantially homogeneous and flowable slurry mixtures are fed into a mold and hardened into a casting whose shape is defined by the shape of the cavity enclosed by the mold. The casting operation may be performed such that a clear and sharp interface between the different substantially homogeneous and flowable slurry mixtures is achieved, or alternatively, it may be performed such that a constant mixing of the two different substantially homogeneous and flowable slurry mixtures occurs at the interface zone.

[0259] In a casting operation that results in a well-defined interface, the first cast portion of the article is allowed to harden to a degree that does not result in intermixing of the substantially uniform, flowable slurry mixture.

[0260] In castings where an interface region is formed between the cast portions of the article, hardening and cooling of the first cast portion can continue as long as limited mixing of the substantially homogeneous, flowable slurry mixture can occur or as long as some melting, softening, or any other modification can occur in the already cast portion. Active or quiescent cooling of the initially cast substantially homogeneous, flowable slurry mixture can be performed in a directed manner such that the hardened region moves through the casting and eventually reaches that side of the cast portion where additional casting is to occur.

[0261] The solidification bath is preferably configured to immerse the mold filled with the substantially homogeneous and flowable slurry mixture for a period of time (e.g., 6, 12 and 24 hours) to create a precursor part of said article by phase inversion. During phase inversion, the volatile organic solvent in said substantially homogeneous and flowable slurry mixture is preferably extracted from the article to adjust, control or manipulate the porosity or pores formed in the resulting article (i.e., precursor part) as minimally as possible. By controlling the cellulosic binder concentration and the volumetric mixture between the binder and the build material, i.e., the metal / ceramic powder content, porous and / or non-porous articles can be cast, which is not feasible with conventional casting methods.

[0262] The solidification bath in which phase inversion of the slurry feedstock stored in the cavity of the mold occurs is preferably a non-solvent liquid (or solidification liquid). The non-solvent liquid may be selected from the group including water, distilled water, pure water, and any combination thereof. Other liquids that are non-solvents for the organic polymer binder may also be used in the present invention. The solidification bath is preferably provided in a container suitable for receiving and immersing the mold therein. In one embodiment, the container storing the solidification bath can receive and simultaneously accommodate one or more molds. The container may have a holding frame removably mounted within the container. The holding frame, having suitable locking members, is preferably configured to secure or hold the mold at a designated position within the solidification bath. The holding frame may further comprise an adjustable mounting such that the frame can be raised above the solidification bath for retrieving the mold, leveled with the container bottom for immersing the mold, etc.

[0263] The debonding means is preferably a post-processing unit, which refers to a mechanism for debonding or removing the organic polymer binder from the precursor part retrieved from its mold. In a preferred embodiment, the debonding means includes either or both of a pyrolysis processing section for performing a pyrolysis process and a solvent debonding processing section for performing a solvent debonding process, followed by a sintering process to produce the final part of the article. The debonding means may also include a sintering processing section.

[0264] The single static or dynamic mixer optionally used in the present invention is preferably configured to solely and instantaneously mix two or more substantially homogenous and flowable slurry mixtures in-situ to form one or a single substantially homogenous and flowable slurry mixture prior to transfer (transport) to a mold.

[0265] A single static mixer or motionless mixer is essentially a mixer that does not include any internal moving mechanical parts. A static mixer is a device that includes one or more substantially stationary mixing elements, e.g., baffles such as blades, plates, vanes, etc., that mix flowing fluids, such as slurry feedstocks, and / or their components through a conduit to create flow division or splitting patterns to achieve mixing, e.g., helical mixing by radial circulation or exchange, in the flowing liquid. Static mixing elements are typically immobile within the conduit, but limited movement of the stationary elements relative to the conduit may occur unless they substantially contribute to the mixing of the flowing fluid. In a static mixer with multiple static mixing elements, these elements can be arranged in series and / or staggered relative to each other. Static mixers are preferably selected to generate a mixed flowing stream, i.e., a substantially uniform and flowable slurry mixture, over a short length of the mixer. Dynamic mixers, on the other hand, are the opposite of the static mixers and preferably include moving parts. The dynamic mixer can mix the slurry feedstock and its components together after or while they are being loaded therein. Other mixers of similar nature could be used in place of the aforementioned mixers, as those skilled in the art would be able to appropriately select.

[0266] In one embodiment, the slurry mix print of the present invention relies on the deposition of a solvent-based binder to form a hardened article. Therefore, controlling the concentration of the organic polymer binder and the ratio between said binder and the binding particles (i.e., metal and / or ceramic powder) is a critical step to ensure that the cast article has sufficient static yield stress to maintain its shape once cast or deposited in the mold.

[0267] To obtain an effectively homogenous mixture, the slurry mixture must be prepared such that both types of feedstock have a small variation in viscosity change over a range of shear rates.

[0268] Different types of powder sizes or shapes result in significant differences in terms of their rheological behavior. Rheological adjustments must be performed within each material and in combinations of both mixtures across all the varying mixtures. Ideally, they should be within the range of about 30-90 vol.% for metals and / or ceramics, about 50-500 g / L and / or 2.5-70 vol.% for said organic polymer binders, and about 1-15 vol.% for additives. An effective mixture that can vary over a wide range of ratios between two materials is not obtained by simply mixing two materials together. As an example, to obtain a flowable mixture suitable for a casting rate of about 10-80 vol.%, it may be required that feedstock material A is very viscous and material B is very liquid in its material state. As both slurries are non-Newtonian in nature, similar shear or pumping rates may result in different volumetric flow rates, which may result in inaccuracies in the mix ratios programmed by the user. Therefore, in the present invention, the rheological profiles of the feedstock materials (i.e., the components of the slurry feedstock) and their mixtures must be achieved and mapped by experimental setup. These rheological profiles are integrated with the design of the material profiles to form a unique compensation factor that should be included during the post-processing of the pure Gcode to ensure that the feeding volume flow rates of both slurries are consistent so that a uniform mixing ratio is obtained. There is an achievable effective mixing ratio between the two materials, i.e., it is usually in the range of about 10-90%. This allows the generation of the formation of metal and ceramic mixtures, i.e., metal A and metal B, metal A (porous mixture) and metal A (non-porous mixture), ceramic A (porous) and ceramic A (non-porous) or ceramic A and ceramic B, depending on the needs and characteristics of the article that needs to be formed. The mixture of materials flowing through the mixer may be three or more materials and is not limited to those shown in any diagram. This configuration allows material A and material B to be mixed in a precise ratio during the casting process.

[0269] An example configuration is shown below. Material A (metal / ceramic A with liquid low concentration binder) and Material B (pure binder with premix of additives). Material A (porous metal / ceramic mixture) is formed by the addition of a skeletal non-soluble material / foaming agent with material A (concentrated mixture), where material A can be selected from the group of metals and ceramics. This allows the casting of unique shell-like structures that are solid and filled with a porous material, which can be filled with a porous material (see Figure 4). The following are non-limiting combinations of construction materials, including metals and ceramics. ·Metal-metal (i) Al-Cu (ii) Al-Ni (iii) Ni-Ti (iv) 316L-H13 (v) “Ti-6Al-4V”-304L (vi) Low carbon steel - high carbon steel (vii)304-304 porous structure Metal-ceramic (i) Al-SiC (ii) Al-Al2O3 (iii) Ni-ZrO2 (iv) Cu-SiC

[0270] ·Ceramic-Ceramic (i) SiC-SiC (different densities) (ii) Al2O3-Al2O3 (porous structure) (iii) Al2O3-SiC (iv) Al2O3-ZrO2 For the transition between low carbon steel and high carbon steel the following compositions can be used:

[0271] Table 13: Composition of the first mixture [Table 13]

[0272] Table 14: Composition of the second mixture [Table 14]

[0273] In the case of the 304-304 porous structure, the porosity of the structure is controlled by the size of the salt crystallization. The following can be used:

[0274] Table 15: Composition of the first mixture [Table 15]

[0275] Table 16: Composition of the second mixture [Table 16]

[0276] The following can be used to transition between clay and low carbon steel:

[0277] Table 17: Composition of the first mixture [Table 17]

[0278] Table 18: Composition of the second mixture [Table 18]

[0279] Further embodiments / aspects A newly invented 3D printing system with a unique composition of metal and / or ceramic powder-binder slurry mixture as feedstock material is presented. The binder used for the metal and / or ceramic mixture consists of said organic polymer binder from the group of cellulose esters, cellulose ethers and their derivatives. It is dissolved in 10-70% by volume of organic solvent as base binder, and combines with additives (dispersants, rheology modifiers, defoamers, or foaming agents) solid particles consisting of 30-90% by volume of one or more metal and / or ceramic powders to form the metal and / or ceramic powder binder slurry mixture.

[0280] In one embodiment of the present invention, the term build material refers to solid particle material or powder of material. The material is mixed as part of the feedstock material preparation. The solid particle size can range from 0.1 to 100 um. The material refers to at least one metal and / or ceramic or a mixture of two or more build materials used in the preparation of the "feedstock" or "slurry mixture" and can be used interchangeably. The binder here refers to the cellulose group consisting only of esters, ethers and derivatives.

[0281] Here, cellulose derivatives of ether and ester groups are to be understood as one type of biobased polymer having ether and ester functional groups linked to its main molecular chain.

[0282] Cellulose ethers are high molecular weight compounds produced by replacing the hydrogen atoms of the hydroxyl groups in the anhydroglucose units of cellulose with R belonging to an alkyl or substituted alkyl group. Examples of cellulose ethers include methyl cellulose and ethyl cellulose.

[0283] Cellulose esters are generally water-insoluble polymers with good film-forming properties, and are classified into organic and inorganic groups. Various types of organic cellulose esters can be used, such as cellulose acetate (CA), cellulose acetate phthalate (CAP), cellulose acetate propionate, cellulose acetate butyrate (CAB), cellulose acetate trimellitate (CAT), and hydroxypropyl methylcellulose phthalate (HPMCP). Inorganic cellulose esters that can be used are cellulose nitrate and cellulose sulfate.

[0284] In a preferred embodiment, the molecular mass of the binder is less than Mw 100,000. A slurry mixture is first prepared by dissolving the binder in a concentration range of 20-70 g per 100 ml of solvent (i.e., purity ≧95%).

[0285] The base binder can be a single type of binder from the group, a similar or mixture of two or more groups with different molecular weights, or a blend of two or more similar groups with different molecular weights in the base binder formulation. Mixtures of different molecular masses or different types of binder groups can achieve the desired rheology and cure control. Similarly, the solvent selected to dissolve the binder can be a single type or a mixture of different solvents depending on the mixture composition in the base binder formulation.

[0286] The solvent used to dissolve the binder is preferably a volatile organic solvent solution, depending on the mixture composition in the base binder formulation. The volatile organic solvent used is preferably ketones and esters.

[0287] Ketones refer to any class of organic compounds characterized by a carbon atom having a carbonyl group covalently bonded to an oxygen atom. The remaining two bonds are to other carbon atoms or to a hydrocarbon radical (R). Examples of ketones include acetone, cyclohexanone, diacetone alcohol, and the like.

[0288] Esters have the general formula RCOOR', where R represents a hydrogen atom, an alkyl group, or an aryl group, and R' can be an alkyl group or an aryl group, but is not a hydrogen atom. If it is a hydrogen atom, the compound is a carboxylic acid. Examples of esters include methyl formate, ethyl lactate, etc.

[0289] Other suitable organic solvents are nitromethane, acetonitrile, methyl glycol, tetrahydrofuran, alcohols, ethers, aromatic solvents, aliphatic solvents and dioxanes.

[0290] Additives such as plasticizers, defoamers or foaming agents can be added to the formulation to obtain the desired rheological behavior and printing properties. The foaming agent allows the user to control the concentration of the printed object through mixing to form the desired porosity during the printing process. By in-situ addition and mixing of the foaming agent, the porosity of the metal part can also be controlled during the printing process. The same approach can be applied to control the binder viscosity, strength, structural and mechanical characteristics of the green part binder, and hardening speed during the printing process. Solid particles, in this case metal and / or ceramic powders, can be prepared by wetting and dispersing the additives premixed with the base binder solution to form a slurry mixture. The mixture is prepared under controlled environment, i.e., under vacuum and / or inert gas conditions.

[0291] Phthalate plasticizers appear colorless with a slight odor and limited solubility in water, but are miscible in a variety of organic solvents. Phthalate esters are produced by esterification of phthalic anhydride, which is obtained by oxidation of orthoxylene.

[0292] Phthalates have the basic structure of benzenedicarboxylic acid with two side chains (R and R') that can be alkyl, benzyl, phenyl, cycloalkyl, or alkoxy groups. The defining characteristics of each phthalate ester and its degradation pattern are determined by the length of the dialkyl side chain. If the phthalate ester is more branched, more isomers are available and it is likely to be hydrophobic. Examples of phthalate plasticizers include dibutyl phthalate, diaryl phthalate, diethyl phthalate, dimethyl phthalate, and di-2-methoxyethyl phthalate.

[0293] The plasticizer is present in an amount of 2-10% by weight based on the total weight of the binder. In addition to the plasticizer ingredients identified above, specific examples of plasticizers may be selected from the group consisting of N-ethyltoluenesulfonamide, o-cresyl p-toluenesulfonate, dibutyl tartrate, acetyltriethyl citrate, triethyl citrate, glycerol, ethylobenzoyl benzoate, ethylphthalylethyl glycolate, methylphthalylethyl glycolate, and the like.

[0294] Here, plasticizer means a component that enhances the plasticity or fluidity of a material. In some embodiments, the component may be introduced as an organic solvent, but as the organic solvent evaporates, it begins to function as a plasticizer. The binder composition includes a plasticizer and at least one organic solvent, so when the organic solvent begins to function as a plasticizer, the binder composition also contains a plasticizer. In other words, the cellulose acetate is plasticized in the solution. In some embodiments, the plasticizer may be the same as at least one of the organic solvents. In other embodiments, the plasticizer is different from any of the organic solvents.

[0295] Antifoaming agents or dispersing agents, also called surfactants (e.g., aryl or alkyl phosphates), can be added as additives to promote the suspension of solid or liquid particles in a liquid (e.g., a colloid or emulsion) to improve particle separation and prevent settling or agglomeration. Other examples of dispersing agents are triethyl phosphate and triphenyl phosphate.

[0296] This embodiment of the solid particulate in the form of a metallic material refers to the group consisting of one or a combination of two or more of the following elements: Stainless Steel: 17-4PH, 304, 304L, 310, 316, 316L, 420, 440, 430L etc. Titanium and titanium alloys: Ti64, Ti-6Al-4V, Ti64ELI, etc. Aluminium and aluminium alloys: AlSi10Mg, AlSi7Mg, ADC12, AlMg5Mn etc. Nickel and Nickel Alloys: 718, 625, Hastelloy® X, Kovar, Invar 36, Hastelloy® C, etc. Other Metals: A2, D2, H13, M2, 4140, CoCr, CoCrMo, Copper Alloys, Bronze, Magnesium, Carbon Steel, Chromoly Steel, Fe-3%Si, Fe-50%Ni, Fe-50%Co, W, WC-5Co, WC-1-Co, etc.

[0297] This embodiment of the solid particulate in the form of a ceramic material refers to the group consisting of one or a combination of two or more of the following elements:

[0298] Calcium phosphate ceramics: Hydroxyapatite (HAp), Tricalcium phosphate (TCP), Amorphous Calcium Phosphates (ACPs), and Biphasic Calcium Phosphates (BCPs) Oxide ceramics: Aluminum oxide, Beryllium oxide, Zirconium dioxide, Yttria-stabilized zirconia (YSZ) Silicate ceramics: porcelain, aluminum silicate, kaolin, magnesium silicate, mullite Carbide ceramics: boron carbide, silicon carbide, tungsten carbide Nitride ceramics: silicon nitride, aluminum silicon oxynitride, aluminum nitride, and mixtures thereof

[0299] The particle mesh size is preferably less than 200.

[0300] The use of the feedstock materials will now be described.

[0301] The feedstock is placed in a sealed storage tank 12 ready to be fed into an extrusion-based 3D printer that can dispense the slurry mixture layer by layer to form a 3D object, as shown in Figure 25. The storage tank 12 is pressurized 15 to transfer the feedstock to a pump 14, which can be a progressive cavity pump, a peristaltic pump, or a syringe, driven by a printer control 16. A nozzle 18 moves and dispenses the feedstock material to form a green part 20.

[0302] The green part 20 can be cured at room temperature or with additional ventilation 22. The green part 20 can be printed on an optional hot plate 24. A heating chamber at 30-100°C can also speed up the curing process. The printed green part 20 has sufficient holding strength for easy handling.

[0303] The printer can be configured with two or more slurry metal and / or ceramic mixtures delivered through separate nozzles 18A, 18B as shown in FIG. 26 to form unique multi-material or separate continuous gradient material structures after post-processing.

[0304] Another configuration for slurry mixture based printing can be performed by in-situ mixing, as shown in Figure 27. A first feed material 26 and a second feed material 28 are fed prior to mixing in a mixer 30 having the following configuration: First configuration: First Feed Material: Binder Solution Second Feed Material: Metal and / or Ceramic Powder Solution Second configuration: First Feed Material: Metal-Binder Slurry Mixture Second Feed Material: Ceramic-Binder Slurry Mixture

[0305] The two feed materials 26, 28 are fed into a mixer 30 during the printing process. Depending on its size, post-curing of the green part 20 may be required to ensure a fully cured structure before proceeding to post-processing steps.

[0306] Post-processing of the print includes a debinding process 32 to form a brown part 34 and a sintering process 36 to form the final sintered part 38. The thermal debinding process 32 and the sintering process 36 can be carried out in a controlled environment, by a single heating process or two separate processes, according to a specific temperature profile for the type of material being processed based on the type of metal and / or ceramic particles. The thermal debinding and sintering profiles are shown in FIG. 29. During thermal debinding, the green part is heated to the thermal decomposition temperature of the binder, and the holding time can be varied depending on the size of the part to ensure complete removal of the binder. This is followed by a sintering process that fuses the metal and / or ceramic particles together at a specific temperature depending on the type of material to be processed. Further post-processing operations such as heat treatment, surface finishing, or machining may be performed.

[0307] [Example 1] Prepare stainless steel 17-4PH using 60% by volume of 17-4PH metal powder with an average particle size of 15 μm, and 40% by volume of binder solution. Prepare a solution of 40 g of binder cellulose acetate per 100 ml of acetone solvent.

[0308] The binder solution contains 10% by volume of additives consisting of a mixture of plasticizers, antifoamers and dispersants.

[0309] The basic printing setup in an unheated environment is shown in Figure 30. This setup produced a green part 20 as shown in Figure 31. After post-processing, a sintered stainless steel 38 is obtained as shown in Figure 32.

[0310] [Example 2] A ceramic mixture is prepared using 70% by volume kaolin and 30% by volume binder solution. 40g of cellulose acetate is prepared in 100ml of acetone solvent. Figure 33 shows the basic printing setup in a non-heated environment. This setup produced a green part 20 as shown in Figure 34. After post-processing, a sintered ceramic 38 is obtained as shown in Figure 35.

[0311] Thus, a feedstock for 3D printing is introduced. The feedstock is made from a metal and / or ceramic slurry mixture. The feedstock can be directly printed to obtain the intended 3D object.

[0312] Although a summary of the inventive subject matter has been described with reference to specific embodiments, various modifications and changes may be made to these embodiments without departing from the broader scope of the disclosed embodiments. Such embodiments of the inventive subject matter are referred to herein by the word "invention," either singly or collectively, for convenience only, and are not intended to automatically limit the scope of this application to any single disclosure or inventive concept when more than one invention is actually disclosed.

[0313] The embodiments illustrated herein are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed.

[0314] Other embodiments may be utilized and derived from those embodiments, such that structural and logical substitutions and changes may be made without departing from the scope of the present disclosure. Therefore, the detailed description is not to be construed in a limiting sense, and the scope of the various embodiments is defined solely by the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0315] As used herein, the term "or" may be interpreted in either an inclusive or exclusive sense. Moreover, herein, a resource, operation, or structure described as an example may be multiple examples. Moreover, boundaries between various resources, operations, modules, engines, and data stores are somewhat arbitrary, and certain operations are illustrated in the context of specific example configurations. Other allocations of functionality are contemplated and may be included within the scope of various embodiments of the invention. In general, structures and functions presented as separate resources in the example configurations may be implemented as combined structures or resources. Similarly, structures and functions presented as a single resource may be implemented as separate resources. These and other variations, modifications, additions, and improvements fall within the scope of the embodiments of the invention as expressed by the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative and not restrictive sense.

[0316] The foregoing description has been provided for purposes of explanation and with reference to specific embodiments. However, the illustrative discussion above is not intended to be exhaustive or to limit the contemplated embodiments to the precise forms disclosed. Many modifications and variations are possible in light of the above teachings. The embodiments have been selected and described in order to best explain the principles involved and their practical application, thereby enabling others skilled in the art to best utilize the various embodiments with various modifications suited to the particular use contemplated.

[0317] It will also be understood that although terms such as "first", "second" and the like are used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first contact can be referred to as a second contact, and similarly, a second contact can be referred to as a first contact, without departing from the scope of the present embodiment. Although a first contact and a second contact are both contacts, they are not the same contact.

[0318] The terms used in the description of the example embodiments herein are merely for the purpose of describing the particular example embodiment and are not intended to be limiting. When used in the description of the example embodiments and the accompanying examples, the singular forms "a", "an" and "the" are intended to include the plural unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will further be understood that the terms "comprise" and / or "comprises" as used herein specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements and / or components, and / or groups thereof.

[0319] As used herein, the term "if" may be interpreted to mean "when" or "after" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrase "if determined" or "if (a described condition or event) is detected" may be interpreted to mean "after determining" or "in response to determining," or "after detecting (a described condition or event)" or "in response to detecting (a described condition or event)," depending on the context.

Claims

1. A method for extrusion-based three-dimensional (3D) printing of a functionally graded article, comprising: Providing a slurry feedstock, Providing a build material comprising a metal, a ceramic, or any combination thereof; providing said build material, which is porous, non-porous, or any combination thereof; providing the build material in an amount of 10% to 90% by volume; Providing an organic polymeric binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof; providing said organic polymer binder comprising providing said organic polymer binder at a concentration of 150 g / L to 550 g / L; providing an additive selected from the group including plasticizers, antifoaming agents, dispersants, sacrificial materials, dissipative materials, scaffolding materials, water soluble inorganic salts, foaming agents, graphene, graphene oxide, flame retardants, toners, release additives, stabilizers, antistatic agents, impact modifiers, colorants, antioxidants, and any combination thereof; providing a volatile organic solvent; mixing the blended build material and the additives to form a first premix; mixing the dissolved organic polymer binder and the volatile organic solvent to form a second premix; mixing the first premix with the second premix to form a substantially uniform, flowable slurry mixture that is printed as a precursor part of the functionally graded article; debinding the organic polymer binder from the precursor part by either or both of a pyrolysis process and a solvent debinding process; and subjecting the precursor part from which the organic polymer binder has been debonded to a sintering process to produce the final part comprising the build material that selectively has a graded composition, configuration including a packing pattern, or any combination thereof that varies across a volume of the final part of the functionally graded article in one or more directions. A method comprising:

2. forming two or more substantially uniform, flowable slurry mixtures, each comprising a respective first premix and a respective second premix; 2. The method of claim 1 .

3. further comprising the step of instantaneously mixing the two or more substantially uniform, flowable slurry mixtures in situ with a static or dynamic mixer to form one substantially uniform, flowable slurry mixture.

3. The method of claim 2 .

4. providing a support structure for the overhang or cantilever portion of the functionally graded article, the support structure comprising a substantially uniform, flowable support mixture formed by a support material; 2. The method of claim 1 .

5. 1. A system for extrusion-based three-dimensional (3D) printing of functionally graded articles, comprising: one or more vessels for containing a slurry feedstock; The slurry feedstock comprises: a build material comprising a metal, a ceramic, or any combination thereof, and being porous, non-porous, or any combination thereof, in an amount of 10% to 90% by volume; an organic polymer binder selected from the group consisting of cellulose esters, cellulose ethers, and derivatives thereof, having a concentration of 150 g / L to 550 g / L; an additive selected from the group including a plasticizer, an antifoaming agent, a dispersant, a sacrificial material, a dissipative material, a scaffolding material, a water soluble inorganic salt, a foaming agent, graphene, graphene oxide, a flame retardant, a toner, a release additive, a stabilizer, an antistatic agent, an impact modifier, a colorant, an antioxidant, and any combination thereof; a volatile organic solvent; mixing the build material and the additives to form a first premix and dissolving the organic polymer binder in the volatile organic solvent to form a second premix, and mixing them to form a substantially uniform and flowable slurry mixture; The system comprises: an injection adjusting means for adjusting the injection of the slurry feedstock contained in the one or more vessels and selected from the group including solenoid valves, mechanical pumps, and combinations thereof; a calculation unit having a control unit configured to generate a control signal for the jetting adjustment means, the control unit being connected to a database comprising a predetermined set of material and rheological profiles used for influencing the control signal functionally on a final part of the functionally graded article; a fluid driver configured to provide fluid pressure to the slurry feedstock contained in the one or more vessels or the injection adjustment means to effect movement of the slurry feedstock contained in the one or more connected vessels to provide a pressurized slurry feedstock, the fluid driver being selected from the group including a pneumatic driver, a hydraulic driver, a mechanical movement device, and any combination thereof; a print head operatively driven by the computing unit and configured to jet the substantially uniform, flowable slurry mixture to create a precursor part of the functionally graded article; the organic polymer binder is debonded from the precursor part by one or both of a pyrolysis process and a solvent debonding process, followed by a sintering process to produce the final part comprising the build material that selectively varies gradually in composition, configuration, including packing pattern, or any combination thereof across a volume of the final part in one or more directions; A system characterized in that

6. the system further comprising a static or dynamic mixer for instantaneously mixing two or more substantially homogenous, flowable slurry mixtures in situ to form a substantially homogenous, flowable slurry mixture prior to transfer to the printhead; 6. The system of claim 5.

7. the one or more containers contain a support material that forms a substantially uniform, flowable support mixture that prints support structures for the overhanging or cantilevered portions of the functionally graded article through the printhead or other printheads; 7. The system according to claim 5 or 6.

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