Particle compositions and methods of preparing and using particle compositions

Abstract

Described are particle compositions that contain metal particles, pore-forming particles, and irregularly-shaped agglomerate particles formed from the metal particles and the pore-forming particles; particle composition that are useful as a feedstock composition in an additive manufacturing process; and methods of using a particle composition as described as a feedstock for forming a porous shaped metal body by an additive manufacturing process.

Description

PARTICLE COMPOSITIONSAND METHODS OF PREPARING AND USING PARTICLE COMPOSITIONSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to United States Provisional Application No. 63 / 707.385, filed on October 15, 2024, the contents of which are incorporated herein by reference in their entirety for all purposes.FIELD

[0002] Described are particle compositions that contain metal particles, pore-forming particles, and irregularly- shaped agglomerate particles formed from the metal particles and the poreforming particles; particle composition that are are useful as a feedstock composition in an additive manufacturing process; and methods of using a particle composition as described as a feedstock for forming a porous shaped metal body by an additive manufacturing process.BACKGROUND

[0003] Additive manufacturing processes are known to be useful for forming shaped bodies, which may be made of polymeric or inorganic (e.g., metal) materials. As one example, additive manufacturing techniques have been studied for forming porous sintered metal bodies that have industrial applications, including filtering of materials used in the electronics and semiconductor manufacturing industries. Porous filters may be used in the semiconductor and microelectronics industries as in-line filters that remove particulate matter from fluids, to prevent introduction of the particulate matter into a manufacturing process. The fluid may be in the form of a gas or a liquid.SUMMARY

[0004] Described as follows are particle compositions that contain (i.e., comprise, consist essentially of, or consist of) metal particles and pore-forming particles, including in the form of agglomerate particles that contain pore-forming particles bonded to metal particles. Also described are methods of preparing the particle compositions, and methods of using a particle composition, e.g., as a feedstock composition in an additive manufacturing process.

[0005] Particle compositions as described, useful for as feedstock for forming porous shaped metal bodies by binder jet additive manufacturing processs, contain metal particles combined with polymeric “pore-forming particles.”

[0006] A challenge when using these types of feedstock compositions for additive manufacturing processses is that the particles of the dry feedstock, i.e., the pore-forming particles and the metal powder, tend to become segregated during use due to the mismatch of density and particle size of the two different types of particles. The lower-density pore-forming particles can become segregated or separated from the higher-density metal particles, causing the pore-forming particles to become airborne or otherwise removed from the feedstock and collect on nearby equipment or components such as a roller, cleaning tank, printing head, or the like, of the additive manfacturing apparatus. This movement of the pore-forming particles often leads to printhead clogging and can otherwise negatively affect the quality of printed products prepared by the apparatus, including by increasing part-to-part variation in quality. It can also cause interruptions in printing operations and require more frequent changing of printheads.

[0007] Particle compositions as described herein can reduce the tendency of pore-forming particles to separate from a particle composition during use, e.g., as a feedstock, because the pore-forming particles and the metal particles are bonded together as agglomerate particles. Pore-forming particles can be made from one or more polymers, such as a thermoplastic polymer, that can be bonded or adhered to the metal particles at elevated temperature. Useful polymer materials include hydrophilic polymers such as polymethylmethacryalte, polyvinyl alcohols, and similar polymers.

[0008] To form the particle composition with agglomerate particles, the metal particles and poreforming particles can be processed at a temperatre that causes the pore-forming particles to soften without melting to cause surfaces of the pore-forming particles to become adhered to the metal particles to form agglomerate particles containing multiple pore-forming particles and multiple metal particles. The agglomerate particles can be processed to provide desired particle size and size distribution properties of the agglomerate particles in the particle composition.

[0009] In one aspect, the disclosure relates to a feedstock composition that contains metal particles and pore-forming particles, including agglomerate particles that comprise pore-forming particles bonded to metal particles.JE000912 WG

[0010] In another aspect, the disclosure relates to a method of preparing a powder composition. The method includes: (i) combining metal particles and pore-forming particles to form a mixture of the metal particles and the pore-forming particles, the pore-forming particles having a glass transition temperature and a melting temperature; and (ii) heating the collection of metal particles and pore-forming particles at a temperature that is greater than the glass transition temperature and below the melting temperature to cause pore-forming particles to become bonded to metal particles.

[0011] According to yet another aspect, the disclosure relates to a method of forming a porous sintered metal body by additive manufacturing steps. The method includes: providing feedstock comprising metal particles, pore-forming particles, including as agglomerate particles that comprise pore -forming particles bonded to metal particles; forming a layer of the feedstock on a surface; selectively applying liquid polymeric binder to areas of the layer of feedstock; solidifying the liquid polymeric binder to form solidified feedstock; forming a second layer of the feedstock over the layer that contains the solidified feedstock; selectively applying liquid polymeric binder to areas of the second layer of feedstock; and solidifying the liquid polymeric binder to form solidified feedstock

[0012] The preceding summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole.BRIEF DESCRIPTION OF THE FIGURE

[0013] FIG. 1 is a scanning electron microscope (SEM) image of agglomerated particles of a feedstock, according to an embodiment of the invention.

[0014] FIG. 2 is an SEM image showing the feedstock powder mixture after being baked at 100°C, according to an embodiment of the invention.

[0015] FIG. 3 is an SEM image showing the feedstock powder mixture after being baked at 200°C, according to an embodiment of the invention.

[0016] FIG. 4 is a chart illustrating the basic flowability energy of the feedstock powder after successive thermal treatment cycles, according to an embodiment of the invention.JE000912 WG

[0017] FIG. 5 is a chart illustrating the specific energy of the feedstock powder after successive thermal treatment cycles, according to an embodiment of the invention.

[0018] FIG. 6 is a graph showing the measured open porosity values for nine different sections of a sintered part fabricated from the feedstock, according to an embodiment of the invention.

[0019] FIG. 7 is a graph showing the Thermogravimetric Analysis (TGA) result for the mixed powder feedstock, illustrating mass loss as a function of temperature.DETAILED DESCRIPTION

[0020] As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

[0021] The following description relates to particle compositions that contain metal particles and pore-forming particles, including agglomerate particles that contain pore-forming particles bonded to metal particles; methods of preparing the particle compositions; and methods of using a particle composition, such as for a feedstock composition in an additive manufacturing process.

[0022] A particle composition (a.k.a. “feedstock composition” or “powder composition”) includes metal particles and pore-forming particles, with at least some of the metal particles and pore-forming particles being in the form of agglomerate particles that are made from (e.g., comprise, consist essentially of, or consist of) multiple metal particles and multiple pore-forming particles bonded together. The powder composition may also contain the metal particles and the pore-forming particles in forms different from the agglomerate particles, including as individual particles among the agglomerate particles.

[0023] The powder composition is prepared from a powder mixture that includes a collection of metal particles sometimes referred to as a “metal powder,” combined with a collection of poreforming particles sometimes referred to as a “pore-forming particle powder” (a.k.a. “poreforming powder”), which is then processed as described herein to form a particle composition that contains agglomerate particles derived from the metal particles and the pore-forming particles.

[0024] The term “metal” as used herein refers to any metallic or metalloid chemical element, or any alloy of two or more of these elements. Useful metal particles may be made of metal thatincludes nickel, nickel alloy, or iron-based alloys such as stainless steel, among others.Exemplary nickel particles contain at least 99 percent by weight nickel based on total weight particles, with no more than a small amount of impurities or other materials. Exemplar}' nickel- based alloy particles may be made of nickel alloys that contain a combination of nickel (e.g., from 45 to 56 weight percent), chromium (e.g., from 15 to 30 weight percent), and molybdenum (e.g., from 8 to 18 weight percent), along with lower amounts of other metals such as iron, cobalt, tungsten, manganese, silicon, carbon, vanadium, and copper. Specific examples of useful nickel alloys include those alloys referred to generically as nickel “Alloy 22” and “Alloy C22.” (e.g., HASTELLOY® C-22®). An example of a useful iron-based alloy is stainless steel, e.g., 316L Stainless Steel.

[0025] A metal powder may contain a collection of metal particles that all have substantially the same chemical composition, substantially the same or similar shapes, and are of the same or comparable size falling within a bell-shaped particle distribution. For example, a metal powder may contain individual metal particles that each comprise, consist essentially of. or consist of the same metal, wherein all or substantially all of the metal particles may contain the same metal and have the same composition.

[0026] Each individual metal particle of a metal powder can be made substantially or entirely of a metal. For example, each individual metal particle is made of at least 90, 95, 99, or 99.9 weight percent of a metal. A metal particle that consists essentially of a metal is a metal particle that contains the metal and not more than 3, 2, 1, or 0.5 weight percent of non-metal material.

[0027] A metal powder can include one or more different types of metal particles; however, exemplary metal powders can contain a collection of individual metal particles that all have the same or similar chemical composition. In some aspects, the composition of the metal powder can be substantially or entirely of metal. For example, in some aspects, a metal powder may contain at least 90, 95, 99. or 99.9 weight percent metal as defined herein. A metal powder that consists essentially of metal is a metal powder that contains metal and not more than 3, 2, 1, or 0.5 weight percent of non-metal material.

[0028] The collection of metal particles, i.e„ the “metal powder,” can contain metal particles in any of various known particle forms or shapes. Individual metal particles have a generally round or spherical shape. Exemplary useful metal particles are round or spherical as opposed to being elongate, irregular, branched, or fibrous in shape. Additionally, or alternatively, in some aspectsthese metal particles may be generally (substantially) unbranched and round, having a relatively low aspect ratio such as, for example, an aspect ratio below 3:1 or below 2:1.

[0029] The metal particles can be of any size (e.g., mean (“D50”) particle size) and may be defined by a range of particle sizes (particle size distribution) that is effective for use as described herein, including small or relatively small particles on a scale of microns (e.g., having an mean size of less than 500 microns, less than 100 microns, less than 50 microns, 10 microns, or less than 5 microns).

[0030] In specific examples, a metal powder may contain metal particles having similar particle sizes within a bell-shaped particle size distribution. Exemplary metal powders may have a relatively small mean particle size (e.g., contains “fine” metal particles), a relatively larger mean particle size (e.g., contains “coarse” metal particles), or may have a mean particle size between “fine” metal particles and “coarse” metal particles.

[0031] An example metal powder that contains coarse metal particles may contain (consist of or consist essentially of) metal particles having a mean (D50) particle size in a range from 25 to 35 micron, and a particles size distribution having D10 < 25 microns and D90 > 45 microns.

[0032] An example metal powder that contains fine metal particles may contain (consist of or consist essentially of) metal particles having a mean (D50) particle size in a range from 3.5 to 4.6 micron, and a particle size distribution having D10 < 4 microns and D90 > 5.5 microns.

[0033] A pore-forming powder contains a collection of polymeric pore-forming particles that can be processed with particles of a metal powder to form a particle composition that contains agglomerate particles. The pore-forming particles in the particle composition (e.g., feedstock composition) act to separate and produce space between the metal particles of the particle composition when the particle composition is used as a feedstock composition in additive manufacturing. These polymeric particles are in solid form as part of a feedstock composition and act to physically separate metal particles within the feedstock and during an additive manufacturing process, to create space between the metal particles and distribute the metal particles with desired levels of spacing and uniformity throughout the feedstock layer, thereby producing a porous shaped body. The pore-forming polymer particles may be used to produce a shaped body with significant porosity.

[0034] Pore-forming polymer particles can be of any useful polymer composition (e.g., thermoplastic), and may be of size that will be useful in combination with metal particles of apowder composition (feedstock composition). Sizes of pore-forming particles may be in a range of sizes also useful for metal particles of feedstock, such as on a scale of microns, e.g., having an average size of less than 100 microns, less than 100 microns, less than 50 microns, 10 microns, or less than 20 microns, for example in a range from 1 to 20 microns.

[0035] Pore-forming particles can be made of a polymer material that is capable of being processed to form the agglomerate particles by bonding or adhering the pore-forming particles to metal particles at elevated temperature. Exemplary polymer materials can be thermoplastic polymers, which may be homopolymers, co-polymers, and polymeric blends. In example particle compositions, the polymer material and the pore-forming particles may be hydrophilic such as, for example, as measured by contact angle. Exemplary polymer materials may have a contact angle that is less than 80 degrees, less than 60, or less than 40 degrees. Contact angle of a polymer material may be measured by known methods using known testing equipment. As an example, contact angle of a polymer material may be measured according to ASTM D7334-08 (Reapproved 2013).

[0036] Specific examples of polymers that may be useful in a polymer material of pore-forming particles include polymethylmethacrylate polymers (e.g., homopolymers and co-polymers) and polyvinyl alcohol polymers (e.g., homopolymers and co-polymers), including blends of these polymers and other thermoplastic polymers.

[0037] A pore-forming powder may contain a collection of pore-forming particles that all have substantially the same chemical composition, substantially the same shape, and are of the same or comparable size (e.g., fall within a bell-shaped particle distribution). For example, a poreforming powder may contain individual pore-forming particles that each comprise, consist essentially of, or consist of the same polymer material, and all or substantially all of the poreforming particles in a pore-forming powder may contain the same polymer material.

[0038] Individual pore-forming particles of a pore-forming powder can be made substantially or entirely of a single polymer material, for example, each individual pore-forming particle is made of at least 90, 95, 99, or 99.9 weight percent of one type of polymer material. A pore-forming particle that consists essentially of a single polymer material is a pore-forming particle that contains the polymer material and not more than 3, 2, 1, or 0.5 weight percent of any other material.

[0039] A pore-forming powder can include one or more different types of pore-forming particles; however, exemplary pore-forming powders can contain a collection of individual poreforming particles that all have the same or similar chemical composition, and the composition of the pore-forming powder can be substantially or entirely of a single polymer material. For example, in some aspects, a pore-forming powder may contain at least 90, 95, 99, or 99.9 weight percent of a single polymer material as defined herein. A pore-forming powder that consists essentially of a single polymer material is a pore-forming powder that contains the polymer material and not more than 3, 2, 1, or 0.5 weight percent of any other metal.

[0040] The pore-forming powder can contain pore-forming particles in any of various known particle forms or shape including a generally round or a spherical shape (sometimes referred to as “pellets”). Examples of useful pore-forming particles are spherical or round, as opposed to being irregular, branched, or fibrous in shape. In some aspects, the pore-forming particles may be generally (substantially) unbranched and round, having a relatively low aspect ratio, e.g., below 3:1 or below 2:1.

[0041] The pore-forming particles can be of any size (e.g., mean (“D50”) particle size) or size range that is effective for use as described herein, including small or relatively small particles on a scale of microns (e.g., having an mean size of less than 500 microns, less than 100 microns, less than 50 microns, 10 microns, or less than 5 microns).

[0042] In specific examples, a pore-forming powder may contain pore-forming particles having similar particle sizes that are within a bell-shaped particle size distribution. The pore-forming particles may have a relatively small mean particle size (e.g., contains “fine” pore-forming particles), a relatively larger mean particle size (e.g., contains “coarse” pore-forming particles), or may have pore-forming particles with a mean particle size between “fine” pore-forming particles and “coarse” pore-forming particles.

[0043] An exemplary pore-forming powder that contains coarse pore-forming particles may contain (consist of or consist essentially of) pore-forming particles having a mean (D50) particle size in a range from 25 to 35 micron, and a particles size distribution having D10 < 25 microns and D90 > 45 microns.

[0044] An exemplary pore-forming powder that contains fine pore-forming particles may contain (consist of or consist essentially of) particles having a mean (D50) particle size in a rangefrom 3.5 to 4.6 micron, and a particle size distribution having DIO < 4 microns and D90 > 5.5 microns.

[0045] A particle composition that contains agglomerate particles can be prepared by forming a powder mixture of the metal powder and the pore-forming powder and processing the mixture using heating and mixing processes to cause the metal particles and polymeric pore-forming particles to become bonded or adhered together upon softening of the pore-forming particles. In general, effective processing methods may include one or multiple steps of: heating the powder mixture under conditions suitable to cause the pore-forming particles to become softened without melting to bond the pore-forming particles to the metal particles and form agglomerate particles; and processing the powder mixture, before or after heating, or both, to adjust the size of the agglomerate particles. A useful heating step can include heating the powder mixture to a temperature that is above the glass transition temperature but below the melting temperature of the pore-forming particles. Useful steps of adjusting the size of the agglomerate particles can include a milling step, e.g., a ball milling step, which reduces the size of the agglomerate particle.

[0046] Examples of such useful processes of forming a particle composition that contains the agglomerate particles can include an initial milling step followed by one or multiple cycles of a heating step and additional milling step. For example, a metal powder (e.g., 316L stainless steel) may be combined with a pore-forming powder (e.g., containing polymethyl methacrylate poreforming particles or polyvinyl alcohol pore-forming particles) and initially dry milled in a ball mill to form a substantially uniform powder mixture. The resulting powder mixture can be heated (“baked”) to a temperature that is above the glass transition temperature but below the melting temperature of the pore-forming particles for an amount of time effective to cause poreforming particles to become bonded to the metal particles to form a first particle composition that contains agglomerate particles. As desired, the first particle composition may be further processed by a second cycle of heating and milling to produce a second particle composition that contains agglomerate particles. As potentially further desired or needed, one or more additional such cycles may be used to adjust the mean particle size or particle size distribution of agglomerate particles in the particle composition. The resulting particle composition will contain agglomerate particles derived from the metal particles and the pore-forming particle, e.g., irregularly-shaped particles formed from multiple metal particles bonded to multiple pore-forming particles. A photomicrograph (prepared using scanning electron microscopy, SEM) of example agglomerate particles is shown at Figure 1.

[0047] The heating and milling steps can be performed to produce a particle composition that has a desired mean particle size and a desired particle size distribution, which can be selected based on factors such as the intended use of the particle composition, the particle sizes of the metal particles in the metal powder and the pore-forming particles in the pore-forming powder, and the manner of processing by heating and milling steps.

[0048] According to exemplary methods using coarse metal particles and coarse pore-forming particles to form a particle composition that contains “coarse agglomerate particles,” a particle composition may contain particles (including agglomerate particles) that are capable of passing through a 100 micron sieve. According to exemplary methods using fine metal particles and fine pore-forming particles to form a particle composition that contains “fine agglomerate particles,” a particle composition may contain particles (including agglomerate particles) that are capable of passing through a 125 micron sieve.

[0049] The particle compositions, as described herein, can be useful as a feedstock composition for use in an additive manufacturing process. Because the pore-forming particles are bonded to or otherwise adhered to the metal particles during use, the feedstock composition will exhibit improved performance by being less susceptible to segregation or separation of the pore-forming particles from the particle composition. The reduced susceptibility to segregation or separation of the pore-forming particles can be related to measured properties of a feedstock composition that include “flowability energy” and “specific energy,” which are understood properties of powders that can be measured using equipment such as an FT4 Powder Rheometer® available commercially from Freeman Technology, Ltd., UK.

[0050] Examples of useful particle compositions that contain coarse agglomerate particles can have a measured basic flowability energy in a range from 270 to 495 millijoule. Examples of useful particle compositions that contain fine agglomerate particles can have a measured basic flowability energy in a range from 190 to 200 millijoule.

[0051] Examples of useful particle compositions that contain fine agglomerate particles can have a measured specific energy in a range from 2.0 to 2.75 millijoule per gram. Examples of useful particle compositions that contain fine agglomerate particles can have a measured specific energy in a range from 6.5 to 7.5 millijoule per gram. A particle composition that contains fineagglomerate particles will have a basic flowability energy that is less than (indicating improved flowability) a mixed powder of the metal particles and pore-forming particles used to prepare the particle composition.

[0052] In the form of a feedstock composition, a particle composition may contain relative amounts of pore-forming particles and metal particles that are useful in an additive manufacturing process to form a porous body having desired properties, including porosity. According to some examples of particle compositions and feedstock compositions useful for preparing a coarse metal membrane, the pore-forming particles may be present in the feedstock in any amount, such as in an amount of from3 to 9 weight percent based on total weight feedstock, with the balance of the feedstock (by weight) being metal particles and optional minor ingredients such as flow aids, dispersants to prevent particle agglomeration, etc. According to some examples of particle compositions and feedstock compositions useful for preparing a fine metal membrane, the pore-forming particles may be present in the feedstock in any amount, such as in an amount of from9 to 15 weight percent based on total weight feedstock, with the balance of the feedstock (by weight) being metal particles and optional minor ingredients such as flow aids, dispersants to prevent particle agglomeration, etc.

[0053] A powder composition as described herein, e.g., a feedstock composition, can be used in an additive manufacturing process (also sometimes referred to as “three-dimensional printing” or (“3D printing”)) to form a shaped body. In some aspects, a powder or feedstock composition, as described herein, can be used in an additive manufacturing process to form a porous sintered metal body such as, by way of example, a porous sintered membrane that is useful as a filter membrane. Useful additive manufacturing process involve multiple steps that sequentially form individual layers of solidified feedstock composition (“solidified feedstock”) that contains the agglomerate particles. Using a series of additive steps, multiple layers of solidified feedstock are formed into a multi-layer composite, each layer being formed separately and in sequence.

[0054] The multi-layer composite contains agglomerate particles dispersed and held in place together by polymeric binder, which is selectively applied to the feedstock. Polymeric binder may be a thermoplastic polymer that may be reversibly heated to form a liquid and then cooled to form a solid (e.g., may be reversibly melted and solidified). Alternately or additionally, a polymeric binder material may be chemically curable, for example by exposure to elevatedtemperature (thermosetting) or by exposure to electromagnetic radiation such as from a laser, e.g., a UV laser.

[0055] According to some aspects, the feedstock composition may be used in a binder jet printing technique. The technique referred to as binder jet printing (also known as “Powder bed and inkjet” printing, “binder jet 3D printing,” and “Drop-On-Powder printing,” and the like), like other additive manufacturing techniques, is a method for making objects described by digital data such as a CAD (computer-aided design) file. Also like other additive manufacturing processes, a three-dimensional body is sequentially built up by a series of individual steps that combine to produce a shaped body in the form of a multi-layer composite made of many thin cross sectional layers. A print head (or other liquid dispensing mechanism) moves across a layer of feedstock, which according to the present invention contains aggregate particles. The print head selectively deposits liquid polymer (“binder,” herein) at portions of the top surface of the feedstock layer. The liquid polymer flows into the feedstock layer and is cooled, dried, or otherwise solidified to form solidified feedstock at portions of the layer. The solidified feedstock contains the agglomerate particles (which contain metal particles and pore-forming particles) and solidified polymeric binder. Multiple feedstock layers are deposited, successively, one over each completed layer, to form the multi-layer composite.

[0056] As needed, the multi-layer composite can be processed to remove polymeric materials and also to cause the metal particles to become bonded together to form a porous sintered metal body. The polymeric materials may be removed by solvent or by heat. The metal particles can become bonded together by heating the body such as, by way of example, sintering.

[0057] The term “sintering” as used herein has a meaning that is consistent with the meaning that this term is given when used in the arts of porous sintered metal structures, such as porous sintered metal membranes of the type that may be used as a metal filter membrane. Consistent therewith, the term “sintering” can be used to refer to processes of bonding (e.g.. “solid state welding” or “fusing”) together a collection of small, sinterable particles of one or more different types (sizes, compositions, shapes, etc.) by applying heat to the particles in a non-oxidizing environment so that surfaces of the particles reach a temperature that causes the particle surfaces to become fused together by a physical (mechanical) bond between the particles surfaces, but that does not cause the particles to melt (i.e.. none of the metal materials reaches its melting temperature).

[0058] A sintering step can be performed at a temperature that is above the sintering point of metal particles, but below the melting temperature of the metal particles. As used herein, a “sintering point” of a particle is a temperature at which the material of the particle is capable of being sintered, i.e., a temperature at which the particles begin adhering to other particles of the body being sintered, and can be fused to another particle, e.g., at a particular pressure such as at atmospheric pressure. A sintering point of a material (e.g.. metal) is normally below a melting temperature of the material, meaning the temperature at which the metal becomes liquid.

[0059] Useful temperatures for performing a sintering step can depend on the composition of the particles and the sintering point of the particles, as well as the size of the particles being sintered, e.g., whether the particles are “coarse” (larger) or “fine” (smaller). For nickel particles, a sintering point may be in a range from 550 to 750 degrees Celsius, and a sintering step may be performed at a temperature in a range from 550 to 800 degrees Celsius. For nickel and stainless steel alloys, a sintering point may be in a range from 950 to 1250 degrees Celsius, and a sintering step may be performed at a temperature in a range from 950 to 1300 degrees Celsius. The sintering step can be performed in a furnace or oven and in a non-oxidizing atmosphere that will not react with or otherwise detrimentally affect the metal particles being sintered, e.g., in a vacuum or in an atmosphere of concentrated or pure hydrogen, concentrated or pure inert gas, or a combination of concentrated or pure hydrogen and inert gas.

[0060] A porous sintered body prepared as described, using agglomerate particles made with metal particles and pore-forming particles, may be relatively porous, e.g., have a porosity in a range from 50 to 60 percent for a coarse metal membrane, and a porosity in a range from 55 to 66 percent for a fine membrane.

[0061] In some aspects, as described herein, the porous sintered body can be useful for forming a filter membrane such as those filter membranes used in the semiconductor manufacturing industry or other industries, such as life sciences, where it is desirable to remove trace amounts of impurities from a process flow.EXAMPLES

[0062] Example 1 : Preparation of Agglomerate Particle Feedstock

[0063] A feedstock composition was prepared by combining a coarse metal powder (316L stainless steel, D50 particle size of 25-35 microns) with a polymeric pore-forming powderJE000912 WG(polymethylmethacrylate, PMMA). The powders were dry mixed in a ball mill at 30 rpm for one hour with a ball-to-powder ratio of 1:2 to create a uniform powder mixture.

[0064] The resulting mixture was then subjected to a multi-cycle thermal treatment process. In each cycle, the powder mixture was baked for 24 hours at a temperature above the glass transition temperature of the PMMA but below its melting point. Following the baking step, the mixture was ball milled again at 30 rpm for one hour.

[0065] The formation of irregularly-shaped agglomerate particles, where the smaller poreforming particles are bonded to the larger metal particles, was confirmed using Scanning Electron Microscopy (SEM). FIG. 2 is an SEM image of the powder mixture after being baked at 100°C, and FIG. 3 is an SEM image of the powder mixture after being baked at 200°C. The images clearly show the formation of agglomerates, reducing the number of free, unbonded particles compared to a simple dry-mixed feedstock.

[0066] Example 2: Flowability Analysis of Thermally Treated Feedstock

[0067] The flowability properties of the feedstock prepared according to the method of Example 1 were measured using an FT4 Powder Rheometer. The basic flowability energy (BFE) and specific energy (SE) were measured for the initial raw powder mixture ("RAW POWDERS") and after each of four successive thermal treatment cycles ("BAKE 1" through "BAKE 4").

[0068] The results are presented in FIG. 4 (Basic Flowability Energy) and FIG. 5 (Specific Energy). As shown in FIG. 4, the BFE of the feedstock after one bake cycle was measured to be approximately 490 mJ, which falls within the range of 270 to 495 millijoules. The BFE continued to decrease with subsequent baking cycles, indicating improved powder flow.

[0069] As shown in FIG. 5. the specific energy of the feedstock after one bake cycle was measured to be approximately 2.1 mJ / g, which falls within the range of 2.0 to 2.75 millijoules per gram. This demonstrates that the thermal treatment process produces an agglomerated feedstock with the desired specific energy characteristics.

[0070] Example 3: Porosity of Sintered Part

[0071] A porous sintered metal disk was fabricated using a binder jetting additive manufacturing process with the thermally treated agglomerate feedstock prepared as described in Example 1. The fabricated part was then sintered to remove the pore-forming material and fuse the metal particles, creating a porous body.JE000912 WG

[0072] To evaluate the uniformity of the final product, the large, sintered disk was sectioned into nine separate pieces. The open porosity of each of the nine pieces was measured. The measurement process involved placing the sectioned parts in distilled water under a vacuum.

[0073] FIG. 6 is a graph showing the open porosity value for each of the nine measured pieces. The measured porosity values are presented in Table 1.JE000912 WGTable 1

[0074] All measured values fall within a range of 53.8% to 55.3%, demonstrating a highly uniform microstructure. The average porosity is approximately 54.3%, which is within the target porosity range of 50 to 65 percent for the final sintered body.

[0075] Example 4: Thermal Analysis of Feedstock

[0076] Thermogravimetric Analysis (TGA) was performed on the mixed powder feedstock to characterize its behavior at elevated temperatures. FIG. 7 shows the TGA result, plotting the percentage of mass remaining as a function of temperature. The analysis shows a significant mass loss occurring between approximately 300°C and 450°C, which corresponds to the decomposition and removal of the polymeric pore-former from the feedstock. This result confirms the temperature window required for the de-binding step prior to final sintering of the metal particles.ASPECTS

[0077] Aspect 1. A feedstock composition comprising metal particles and pore-forming particles, including agglomerate particles that comprise pore-forming particles bonded to metal particles.

[0078] Aspect 2. The feedstock composition of aspect 1, wherein the metal particles have a particle size (D50) in a range from 25 to 35 micron, and a particle size distribution having D10 < 25 microns and D90 > 45 microns.

[0079] Aspect 3. The feedstock composition of aspect 2, wherein the agglomerate particles can pass through a 100 micron sieve.

[0080] Aspect 4. The feedstock composition of aspect 1, wherein the metal particles have a particle size (D50) in a range from 3.5 to 4.5 micron, and a particle size distribution having D10 < 4 microns and D90 > 5.5 microns.

[0081] Aspect 5. The feedstock composition of aspect 4, wherein the agglomerate particles can pass through a 125 micron sieve.

[0082] Aspect 6. The feedstock composition of aspect 1, wherein the agglomerate particles are irregularly-shaped.

[0083] Aspect 7. The feedstock composition of aspect 1, wherein the pore-forming particles are hydrophilic and comprise polymer material having a contact angle that is less than 80 degrees.

[0084] Aspect 8. The feedstock composition of aspect 1, wherein the pore-forming particles comprise a polymer selected from polymethylmethacrylate particles and polyvinyl alcohol particles.

[0085] Aspect 9. The feedstock composition of aspect 1, wherein the metal particles comprise iron-based alloy particles, nickel particles, or nickel-based alloy particles.

[0086] Aspect 10. The feedstock composition of aspect 2 or 3, having a basic flowability energy in a range from 270 to 495 millijoule.

[0087] Aspect 11. The feedstock composition of aspect 4 or 5. having a basic flowability energy in a range from 190 to 200 millijoule.

[0088] Aspect 12. The feedstock composition of any of aspects 2, 3, or 10, having a specific energy in a range from 2.0 to 2.75 millijoule per gram.

[0089] Aspect 13. The feedstock composition of any of aspects 4, 5, or 11, having a specific energy in a range from 6.5 to 7.5 millijoule per gram.

[0090] Aspect 14. A method of preparing a powder composition, the method comprising: (i) combining metal particles and pore-forming particles to form a mixture of the metal particles and the pore-forming particles, the pore-forming particles having a glass transition temperature and a melting temperature; and (ii) heating the collection of metal particles and pore-forming particles at a temperature that is greater than the glass transition temperature and below the melting temperature to cause pore-forming particles to become bonded to metal particles.

[0091] Aspect 15. The method of aspect 14, wherein the heating of (ii) produces a collection of agglomerate particles comprising pore-forming particles bonded to metal particles, and the method further comprises: (iii) milling the collection of agglomerate particles to form a collection of milled agglomerate particles.

[0092] Aspect 16. The method of aspect 15, further comprising, after (iii) milling, repeating (ii) heating and (iii) milling to form a collection of milled agglomerate particles.

[0093] Aspect 17. The method of aspect 15 or 16, wherein the metal particles have a particle size (D50) in a range from 25 to 35 micron, and a particle size distribution having DIO < 25 microns and D90 > 45 microns.

[0094] Aspect 18. The method of aspect 17, wherein the agglomerate particles can pass through a 100 micron sieve.

[0095] Aspect 19. The method of aspect 17 or 18, wherein the powder composition has a basic flowability energy in a range from 270 to 495 millijoule.

[0096] Aspect 20. The method of any of aspects 17, 18, or 19, wherein the powder composition has a specific energy in a range from 2.0 to 2.75 millijoule per gram.

[0097] Aspect 21. The method of aspect 15 or 16, wherein the metal particles have a particle size (D50) in a range from 3.5 to 4.5 micron, and a particle size distribution having D10 < 4 microns and D90 > 5.5 microns.

[0098] Aspect 22. The method of aspect 21, wherein the agglomerate particles can pass through a 125 micron sieve.

[0099] Aspect 23. The method of aspect 21 or 22, wherein the collection of milled agglomerate particles has a basic flowability energy that is less than a basic flowability energy of the collection of the metal particles and the pore-forming particles of step (i).

[0100] Aspect 24. The method of any of aspects 21, 22, or 23, wherein the collection of milled agglomerate particles has a basic flowability energy in a range from 190 to 200 millijoule.

[0101] Aspect 25. The method of any of aspects 21 through 24, wherein the collection of milled agglomerate particles has a specific energy in a range from 6.5 to 7.5 millijoule per gram.

[0102] Aspect 26. The method of aspect 14, wherein the pore-forming particles are hydrophilic.

[0103] Aspect 27. The method of aspect 14, wherein the pore-forming particles comprise polymethylmethacrylate or polyvinyl alcohol.

[0104] Aspect 28. The method of aspect 14, wherein the metal particles comprise ironbased alloy particles, nickel particles, or nickel-based alloy particles.

[0105] Aspect 29. A method of forming a porous sintered metal body by additive manufacturing steps, the method comprising: providing a feedstock comprising metal particles and pore-forming particles, including agglomerate particles that comprise pore-forming particles bonded to metal particles; forming a layer of the feedstock on a surface; selectively applying aliquid polymeric binder to areas of the layer of feedstock; solidifying the liquid polymeric binder to form solidified feedstock; forming a second layer of the feedstock over the layer that contains the solidified feedstock; selectively applying a liquid polymeric binder to areas of the second layer of feedstock; and solidifying the liquid polymeric binder to form solidified feedstock.

[0106] Aspect 30. The method of aspect 29, further comprising forming a multi-layer composite comprising the solidified feedstock.

[0107] Aspect 31. The method of aspect 30, further comprising sintering the multi-layer composite to form a porous sintered metal body.

[0108] Aspect 32. The method of aspect 31, wherein the porous sintered metal body has a porosity in a range from 50 to 65 percent.

[0109] Aspect 33. A porous membrane made according to the method of any of aspects 29-32.

[0110] Having thus described several illustrative embodiments of the present disclosure, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Numerous advantages of the disclosure covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respect, only illustrative. The disclosure’s scope is, of course, defined in the language in which the appended claims are expressed.

Claims

What is claimed is:

1. A feedstock composition comprising metal particles and pore-forming particles, including agglomerate particles that comprise pore-forming particles bonded to metal particles.

2. The feedstock composition of claim 1, wherein the metal particles have: a particles size (D50) in a range from 25 to 35 micron, and a particles size distribution having DIO < 25 microns and D90 > 45 microns.

3. The feedstock composition of claim 1, wherein the metal particles have: a particles size (D50) in a range from 3.5 to 4.5 micron, and a particles size distribution having DIO < 4 microns and D90 > 5.5 microns.

4. The feedstock composition of claim 1, wherein the agglomerate particles are irregularly- shaped.

5. The feedstock composition of claim 1, wherein the pore-forming particles are hydrophilic and comprise polymer material having a contact angle that is less than 80 degrees.

6. The feedstock composition of claim 5, wherein the pore-forming particles comprise polymer selected from polymethylmethacrylate particles and polyvinyl alcohol particles.

7. The feedstock composition of claim 2, having a basic flowability energy in a range from 270 to 495 millijoule.

8. A method of preparing a powder composition, the method comprising:(i) combining metal particles and pore-forming particles to form a mixture of the metal particles and the pore-forming particles, the pore-forming particles having a glass transition temperature and a melting temperature, and(ii) heating the collection of metal particles and pore-forming particles at a temperature that is greater than the glass transition temperature and below the melting temperature to cause pore-forming particles to become bonded to metal particles.

9. The method of claim 8, comprising:(ii) heating the collection of metal particles and pore-forming particles at a temperature that is greater than the glass transition temperature and below the melting temperature to cause pore-forming particles to become bonded to metal particles, to produce a collection of agglomerate particles comprising pore-forming particles bonded to metal particles, and(iii) milling the collection of agglomerate particles to form a collection of milled agglomerate particles.

10. The method of claim 9, comprising, after (iii) milling, repeating (ii) heating and (iii) milling to form a collection of milled agglomerate particles.

11. The method of claim 8, wherein the metal particles have a particle size (D50) in a range from 25 to 35 micron.

12. The method of claim 8, wherein the metal particles have a particle size (D50) in a range from 3.5 to 4.5 micron.

13. The method of claim 8, wherein the pore-forming particles are hydrophilic.

14. The method of claim 11, wherein the powder composition has a basic flowability energy in a range from 270 to 495 millijoule.

15. A method of forming a porous sintered metal body by additive manufacturing steps, the method comprising: providing feedstock comprising metal particles, pore-forming particles including agglomerate particles that comprise pore-forming particles bonded to metal particles,forming a layer of the feedstock on a surface, selectively applying liquid polymeric binder to areas of the layer of feedstock, solidifying the liquid polymeric binder to form solidified feedstock, forming a second layer of the feedstock over the layer that contains the solidified feedstock, selectively applying liquid polymeric binder to areas of the second layer of feedstock, and solidifying the liquid polymeric binder to form solidified feedstock.

16. The method of claim 15, comprising forming a multi-layer composite comprising the solidified feedstock.

17. The method of claim 16, comprising sintering the multi-layer composite to form a porous sintered metal body.

18. The method of claim 17, wherein the porous sintered metal body has a porosity in a range from 50 to 65 percent.

19. A porous membrane made according to the method of claim 15.

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