Method of producing densified articles

Abstract

Methods for densifying articles produced by additive manufacturing processes, such as binder injection processes and laser powder bed melting processes, are described herein. The method can be used for manufacturing beryllium-containing articles. The article may have open cavity, designed internal structural features. In one embodiment, the method uses a sintering step prior to isostatic pressing.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Provisional Application No. 63 / 516,978, filed August 1, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for producing densified articles using an additive manufacturing process. Specifically, this invention relates to producing articles using a binder-jetting additive manufacturing process, and densifying the articles by sintering before applying isostatic pressing using load-transfer powder. Background Technology

[0004] Additive manufacturing is an advanced manufacturing technology that creates complex shapes by adding material layer by layer. This is significantly different from traditional subtractive manufacturing, forming, and other conventional methods of parts manufacturing. Additive manufacturing is a production technology that enables the rapid and flexible production of parts, including prototypes, end-use components, and tooling. By building layer by layer, additive manufacturing utilizes computer-aided design (CAD) modeling software, providing designers with greater freedom in creating three-dimensional (3D) products. This construction method allows manufacturers to design geometries, internal features, and other structures that are difficult or impossible to form using traditional subtractive manufacturing techniques.

[0005] First, a digital blueprint of the desired physical object is created. This virtual blueprint is then divided into digital cross-sections / layers. Each layer begins by spreading a thin layer of metal powder on a bed or platform. The metal powder can be selectively bonded to the object to be formed. A piston supporting the bed / platform descends within the build chamber to spread the next layer of powder and selectively bond it. This sequential layering process is repeated continuously until the desired part is constructed. After heat treatment, unbonded powder is removed, resulting in a semi-finished part.

[0006] Additive manufacturing offers numerous advantages, including significantly reducing the time from design to prototyping to commercialization. Demonstration units and parts can be produced rapidly. Parts can be made into any geometry, typically using ceramics, metals, polymers, and composites. Local control over material composition, microstructure, and surface texture is possible. Design changes are feasible. Multiple parts can be built into a single assembly. There is no need to create complex, potentially one-time-use molds or tooling before prototyping. The energy required to manufacture these three-dimensional solid objects is minimal. It also reduces waste and raw material usage. Additive manufacturing also facilitates the production of extremely complex geometries. Supporting materials can be used to create overhangs, undercuts, and internal spaces. Because parts can be rapidly manufactured on-site as needed, additive manufacturing also reduces a company's part inventory.

[0007] Additive manufacturing methods include electron beam melting and sintering, and laser melting and sintering. Both electron beam and laser methods can be used to sinter or fuse a given cross-section onto an underlying layer. In electron beam melting, loose metal powder cross-sections are melted or fused by an electron beam after metal powder deposition. In laser sintering, a laser beam is used to sinter loosely compacted metal powder cross-sectional areas. The term "sintering" refers to the process by which particles adhere to a solid mass under the influence of external energy. Laser sintering also fuses a specific cross-section to an underlying sintered cross-section. Metal powder not struck by the laser beam remains loose and detaches when the finished part is removed from the forming bed. Alternatively, powder can be removed from the finished part by vacuum cleaning or using fluids such as compressed air to remove any loose powder. Subsequent finishing processes can also be applied to the part to achieve desired properties. These steps include, but are not limited to, further curing, sintering, impregnation, annealing, and final surface treatment.

[0008] Another manufacturing method includes binder spray molding. In binder spray molding, after metal powder is deposited, a liquid binder is selectively deposited to bond the powder particles together. The final part is formed by layer-by-layer deposition of powder and binder. Binder spray molding can produce green blanks. The term "green blank" or "green body" refers to an article or preform produced for further processing using other manufacturing techniques. For example, a metal green blank can be further processed by sintering in an oven or impregnating with at least one metal. Impregnation fills the voids inside the sintered preform.

[0009] U.S. Patent No. 11,400,516 describes a method for producing a three-dimensional model using additive manufacturing. The method involves constructing a green compact layer by layer using a powder material (e.g., an aluminum alloy) and a curable non-powder material. The green compact contains a usable green compact model. The cured non-powder material is removed from the green compact, thereby extracting the usable green compact model from the green compact, and the density of the usable green compact model is increased by cold isostatic pressing (CIP). The usable green compact model is then sintered to produce a three-dimensional model.

[0010] US Patent Publication No. 2023 / 0059163 describes an additive manufacturing technique that enables densification of green preforms prior to subsequent article processing. The article forming method includes: providing a powder composition and forming the powder composition into a green preform using one or more additive manufacturing techniques; contacting the green preform with a powder pressure transmission medium; and then subjecting the green preform and the powder pressure transmission medium to cold isostatic pressing (CIP) or hot isostatic pressing (WIP) at a pressure below the minimum isostatic pressure of the powder pressure transmission medium to obtain a densified green preform.

[0011] High-quality products still need to be produced using additive manufacturing processes. Summary of the Invention

[0012] The method described herein is used to densify articles (e.g., green or melt-formed articles) produced by additive manufacturing processes before further processing. Typically, this method utilizes additive manufacturing to construct complex articles, followed by isostatic pressing to increase the article's density. The resulting article exhibits improved mechanical properties.

[0013] In one aspect, a method for densification is provided, comprising: depositing metal powder using an additive manufacturing process to form a first preform; sintering the first preform at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in load-transfer powder within an enclosed space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article. In one embodiment, the first preform has an open cavity, which is a designed structural feature located inside the first preform. In some embodiments, the first preform may have multiple open cavities. Preferably, the open cavity occupies at least 5% of the volume of the first preform. The apparent density of the densified article may be greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0014] The metal powder may contain beryllium. In one embodiment, the metal powder contains at least 95% by weight of beryllium, based on the total weight of the metal powder. The metal powder contains less than 1% by weight of cobalt and / or nickel, based on the total weight of the metal powder. The metal powder may have a spherical or cylindrical shape, but may also have an irregular shape. In one embodiment, at least 50% of the metal powder has an aspect ratio of 2:1 to 1:1. In one embodiment, the average diameter of the metal powder is less than or equal to 45 micrometers. Bimodal powder may also be used. In one embodiment, the metal powder has a bimodal distribution, with a ratio of coarse metal powder to fine metal powder of 10:1 to 2:1, preferably 8:1 to 4:1, wherein the average diameter of the coarse metal powder is 50 to 400 micrometers, and the average diameter of the fine metal powder is 25 to 40 micrometers.

[0015] In one embodiment, isostatic pressing includes cold isostatic pressing or hot isostatic pressing. Hot isostatic pressing can be performed at a temperature of up to 1150°C and a pressure range of 30 MPa to 175 MPa. Prior to isostatic pressing, a first preform is coated with a load-transfer powder. The load-transfer powder can be a ceramic powder. In one embodiment, the load-transfer powder comprises alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica, or a combination thereof.

[0016] In one aspect, a method for densification is provided, comprising: depositing metal powder using an additive manufacturing process (preferably a binder spraying process) to form a green body; sintering the green body at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in a load-transfer powder within an enclosed space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article. In one embodiment, the green body has an open cavity, which is a structural feature designed into the interior of the green body. In some embodiments, the green body may have multiple open cavities. The apparent density of the densified article may be greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0017] In one aspect, the present invention provides a method for densification, comprising: depositing metal powder using an additive manufacturing process (preferably laser powder bed fusion) to form a molten article; sintering the molten article at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in a load-transfer powder within a closed space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article. In one embodiment, the molten article has an open cavity, which is a structural feature designed into the interior of the molten article. In some embodiments, the molten article may have multiple open cavities. The apparent density of the densified article may be greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0018] These and other non-restrictive features will be described in more detail below. Detailed Implementation

[0019] The invention can be more readily understood by referring to the following detailed description of the desired embodiments and examples included therein. However, the elements, apparatus, and methods described herein are not limited to the specific embodiments and examples presented in the detailed description. It should be understood that these embodiments are merely illustrative of the principles of the invention. Many modifications and adjustments can be readily made to the invention by those skilled in the art without departing from its spirit and scope.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art. In case of conflict, this document (including definitions) shall prevail. Although similar or equivalent methods and materials to those described herein may be used in practice or testing of this disclosure, preferred methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and are not intended to limit the scope of the invention.

[0021] The singular forms “a,” “a,” and “the” include plural references unless the context clearly indicates otherwise.

[0022] As used in the specification and claims, the word "comprising" can include embodiments described as "consisting of" and "mainly composed of". The words "comprising", "including", "having", "having", "may", "containing", and variations thereof, as used herein, are intended as open-ended transitional phrases requiring the presence of the listed ingredients / steps while allowing for the presence of other ingredients / steps. However, such descriptions should also be understood to describe a composition or method as "consisting of" and "mainly composed of", which only allows for the presence of the listed ingredients / steps and any impurities that may arise therefrom, while excluding other ingredients / steps.

[0023] The numerical values ​​relating to polymers or polymer compositions in this application specification and claims reflect average values ​​of compositions of individual polymers that may contain different properties. The numerical values ​​disclosed herein should be understood to include: values ​​that are identical when simplified to the same number of significant figures, and values ​​that differ from the stated values ​​by less than the experimental error of conventional measurement techniques described in this application.

[0024] All ranges disclosed herein include the stated endpoints and can be combined independently (e.g., the range “1 micrometer to 40 micrometers” includes both the endpoints of 1 micrometer and 40 micrometers, as well as all intermediate values). The endpoints and any values ​​of the ranges disclosed herein are not limited to precise ranges or values; their precision is low enough to include values ​​that approximate these ranges and / or values.

[0025] As used herein, approximate language can be used to modify any quantitative representation, as long as the representation can change without altering its fundamental function. Therefore, in some cases, values ​​modified by terms such as “approximately” and “roughly” may not be limited to the specified exact value. The modifier “approximately” should also be considered as disclosing a range defined by the absolute values ​​of the two endpoints. For example, “approximately 2 to approximately 4” also discloses a range of “2 to 4”. The term “approximately” can refer to plus or minus 10% of the indicated number. For example, “approximately 10%” can represent a range of 9% to 11%, and “approximately 1” can represent a range of 0.9 to 1.1.

[0026] For the numerical ranges listed in this article, each intermediate number with the same precision is explicitly considered. For example, for the range of 6-9, in addition to 6 and 9, the numbers 7 and 8 are also considered; for the range of 6.0-7.0, the numbers 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly considered.

[0027] The embodiments described herein provide a method for densifying an article of manufacture, the method comprising using additive manufacturing technology to provide metal powder to form a first preform. In one embodiment, when using a binder spraying process, the first preform may be a green preform; when using a laser powder bed melting process, the first preform may be a molten article of manufacture. For the purposes of this disclosure, the method employs a sintering process after additive manufacturing but before isostatic pressing. After sintering, the method comprises encapsulating the dense body in load-transfer powder, and then isostatically pressing the dense body and the load-transfer powder together. Therefore, this method enables the efficient production of dense articles of manufacture using additive manufacturing processes.

[0028] The method described herein uses additive manufacturing technology to construct three-dimensional articles in a layer-by-layer manner. Various additive manufacturing techniques can be used to form the first preform, including VAT photopolymerization, material jetting, binder jetting, material extrusion, powder bed melting, sheet lamination, or directional energy deposition. Powder bed melting includes direct metal laser sintering, electron beam melting, selective thermal sintering, selective laser melting, and selective laser sintering. In one embodiment, the method employs an additive manufacturing technique using a powder bed, such as binder jetting or powder bed melting. For the purposes of this disclosure, the additive manufacturing process will be described using binder jetting or powder bed melting as examples, but it should be understood that other additive manufacturing techniques may also be used.

[0029] Similar to additive manufacturing, this method first constructs a model of the article. This is typically done using a computer-aided design (CAD) model. The CAD model is then sliced ​​into layers. In binder jetting, these sliced ​​layers detail the design parameters of the part to be formed, including open cavities. The binder jetting apparatus spreads a layer of powder composition within the forming cassette. Any suitable technique can be used to deposit the initial layer, including spreading, coating, brushing, rolling, spraying, or dispensing. The deposited layer can be a thin layer of powder. After each layer is deposited, the printing mechanism selectively applies a jetting fluid called binder to the forming surface, based on the model. The forming surface refers to the uppermost surface within the forming cassette at any given time. After the binder is deposited, the forming cassette is moved and another layer of powder is deposited. In most processes, lowering the position of the forming cassette is more convenient. This process is repeated until the first preform or green body is formed based on the model. In some embodiments, the process may include drying between each layer deposition. Overall, the binder jetting process is a cold process that does not require heating, which prevents stress from being introduced into the article. Furthermore, the molded part is supported during the process due to the powder surrounding the molding chamber. Before removing the first preform from the molding chamber, a curing step can be used to activate the binder. The loose powder is then removed to obtain the first preform.

[0030] In one embodiment, the first preform has at least one open cavity, such as an internal cavity, like a slit, channel, orifice, groove, or other hollow region. This open cavity is a structural design feature of the article, unlike voids, holes, or cracks. The open cavity is not filled or densified, whereas voids, holes, or cracks are densified during the process. Therefore, during densification, it is preferable to preserve the open cavity to prevent it from being blocked, filled, or otherwise disrupting the structure. In one embodiment, at least 5% of the volume of the article may be an open cavity, for example, at least 10%, at least 15%, at least 20%, or at least 25% of the volume. Preferably, the open cavity is located internally.

[0031] For binder spraying processes, the binders that can be used in this process include organic binders that decompose below the sintering temperature. In one embodiment, suitable binders may include, but are not limited to, organic-based binders such as phenolic, polyolefin, polyester, polyether, polyamide, polyesteramide, and polyvinylpyrrolidone-based binders. Examples of such organic-based binders include polyethylene glycol, polyethylene, polylactic acid, polyacrylic acid, polypropylene, and combinations thereof. The organic binder can be cured at low temperatures, for example, between 90°C and 140°C, such as 105°C to 130°C, or 110°C to 125°C. The curing time can be determined as needed, but is preferably less than 6 hours, for example, less than 5 hours or less than 4 hours. Laser powder bed melting processes do not use binders.

[0032] In one embodiment, the metal powder comprises beryllium. The metal powder may contain at least 95% by weight of beryllium, based on the total weight of the metal powder, for example, at least 96% by weight, at least 97% by weight, at least 98% by weight, or more preferably at least 99% by weight. In terms of content range, the metal powder may contain from 95% by weight to 100% by weight of beryllium, based on the total weight of the metal powder, for example, 95% by weight to 99.9% by weight, 96% by weight to 99.5% by weight, or 97% by weight to 99% by weight. The metal powder may contain other metals, but high-purity beryllium is preferred. In one embodiment, the metal powder contains less than or equal to 1% by weight of cobalt, based on the total weight of the metal powder, for example, less than 0.75% by weight, less than 0.5% by weight, less than 0.25% by weight, or less than 0.1% by weight. In one embodiment, the metal powder contains less than or equal to 1% by weight of nickel, based on the total weight of the metal powder, for example, less than 0.75% by weight, less than 0.5% by weight, less than 0.25% by weight, or less than 0.1% by weight. Other metals may also be present, but preferably their content does not exceed the weight percentage of cobalt or nickel, respectively. The composition of the metal powder is preferably kept homogeneous during deposition in the molding cassette to prevent particle segregation that could lead to inconsistent results.

[0033] The morphology of the metal powder can be irregular, polygonal, spherical, or a combination thereof. The morphology can be determined by scanning electron microscopy (SEM) images. In one embodiment, at least 50% of the metal powder has an aspect ratio of 2:1 to 1:1, for example, at least 60% of the metal powder has an aspect ratio of 2:1 to 1:1, or at least 75% of the metal powder has an aspect ratio of 2:1 to 1:1.

[0034] In some embodiments, the metal powder exhibits a Gaussian particle size distribution. The average diameter (d50) of the metal powder (preferably containing beryllium) can be less than or equal to 45 micrometers, for example, less than or equal to 40 micrometers, less than or equal to 35 micrometers, less than or equal to 30 micrometers, less than or equal to 25 micrometers, or less than or equal to 20 micrometers. In terms of particle size range, the average diameter (d50) of the metal powder can be from 1 to 45 micrometers, for example, 1 to 40 micrometers, 5 to 40 micrometers, 5 to 35 micrometers, 5 to 30 micrometers, or 10 to 25 micrometers. The particle size range of the metal powder allows it to be deposited in a molding cassette in a suitable manner. The particle size distribution corresponding to 50% of the cumulative distribution curve is called the average particle size.

[0035] In other embodiments, the metal powder may have a bimodal distribution. The bimodal distribution may have a ratio of coarse to fine particles. The average diameter (d50) of the coarse particles may be greater than or equal to 50 micrometers, for example, greater than or equal to 55 micrometers, greater than or equal to 60 micrometers, or greater than or equal to 75 micrometers. The average diameter (d50) of the coarse particles may range from 50 to 400 micrometers, for example, 50 to 300 micrometers or 75 to 150 micrometers. The average diameter (d50) of the fine particles may be less than or equal to 40 micrometers, for example, less than or equal to 30 micrometers, less than or equal to 25 micrometers, or less than or equal to 10 micrometers. The average diameter (d50) of the fine particles may range from 0.01 to 40 micrometers, for example, 0.5 to 40 micrometers, 1 to 40 micrometers, 1 to 35 micrometers, 5 to 35 micrometers, or 20 to 35 micrometers. The preferred particle size range for the fine particles may be 25 to 40 micrometers, for example, 30 to 40 micrometers or 30 to 35 micrometers. The fine particles may be nanoscale, and in some embodiments may be less than 1 micrometer. Therefore, the particle size range of nanoscale fine particles can be from 1 nanometer to 950 nanometers, for example, 10 nanometers to 700 nanometers or 50 nanometers to 550 nanometers. The ratio of coarse to fine particles in the bimodal distribution can be from 10:1 to 2:1, for example, 8:1 to 3:1, 8:1 to 4:1, or 6:1 to 4:1. Coarse and fine particles can have similar morphologies, i.e., both are spherical, or they can have different morphologies, including different aspect ratios.

[0036] The apparent density of a metal powder may be greater than 50% of its theoretical density, for example, greater than 60%, greater than 70%, or greater than 80%. Apparent density can be evaluated using a Carney funnel according to ASTM standard B417 (Standard Test Method for Determining Apparent Density of Non-Free-Flowing Metal Powders Using a Carney Funnel).

[0037] In addition to apparent density, metal powders also have tap density. In one embodiment, the tap density may be greater than 60% of its theoretical density, for example, greater than 65%, greater than 70%, or greater than 80%. Tap density can be measured using a graduated cylinder according to ASTM standard B527 (Standard Test Method for Tap Density of Metal Powders and Compounds). The measurement method involves mechanically tapping the powder until minimal further volume change is observed. Tap density can be calculated by dividing the mass by the final volume of the metal powder.

[0038] In one embodiment, the method includes depositing metal powder, contacting the metal powder with a binder, curing the binder, and removing a first preform from the loose metal powder. The loose metal powder may be reprocessed as needed. The method may also include sintering the first preform at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense preform. In one embodiment, the heat treatment may be performed at a temperature of 850°C to 1250°C, for example, 900°C to 1150°C, 900°C to 1125°C, or 925°C to 1050°C. During sintering, the temperature is increased to sufficiently volatilize, decompose, or otherwise remove most of the binder from the first preform. For binder spraying processes, preferably, the sintered first preform (green) contains less than or equal to 2.0% by weight, for example, less than 1.5% by weight or less than 1.0% by weight of binder, based on the weight of the first preform. In some embodiments, sintering is sufficient to remove all binder from the green preform. The amount of residual binder after sintering should preferably be low enough to avoid affecting the mechanical properties of the densified product.

[0039] Other processes use a sintering step after isostatic pressing. This embodiment found that sintering before isostatic pressing can improve the production of dense products.

[0040] The sintering step may result in a reduction in the size of the first preform. While this reduction can be considered and predicted in the model, it is preferable to control the size reduction during the sintering step to prevent excessive reduction. In one embodiment, the sintering time should be long enough that the size reduction of the first preform does not exceed 20% of its volume (based on the volume of the first preform). Preferably, the size reduction does not exceed 15%, 10%, or 5% of its volume.

[0041] In one embodiment, the sintering temperature is raised above the solidus temperature of the beryllium-containing metal powder, but below its liquidus temperature. This facilitates the fusion of beryllium particles together via metallic bonds. The time required to heat the first blank can vary depending on the selected sintering temperature and the size and geometry of the first blank. The sintering time should be sufficient to achieve at least 70% of the theoretical density, preferably 70% to 90%, and more preferably 70% to 80%. Isostatic pressing in subsequent steps can achieve additional densification.

[0042] In one embodiment, the method includes isostatic pressing to obtain a densified article. The densified article after isostatic pressing has a higher theoretical density than the theoretical density after sintering. By using isostatic pressing, this embodiment can obtain a densified article with reduced internal defects (including voids). Under certain conditions, this can significantly reduce or eliminate residual porosity. Specifically, the method may include encapsulating a dense body in a load-transfer powder within a closed space and performing isostatic pressing on the dense body and the load-transfer powder to obtain a densified article. The dense body can be completely encapsulated by the load-transfer powder, such that the load-transfer powder is in direct contact with the dense body.

[0043] In one embodiment, the load-transfer powder is a ceramic powder. The ceramic powder may include alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica, or combinations thereof. In a preferred embodiment, the load-transfer powder is alumina. The ceramic powder may be a loose powder. In one embodiment, the ceramic powder may infiltrate structural features of the compacted body, including at least one open cavity, such as an internal cavity, like a gap, channel, orifice, groove, or other hollow region. The open cavity is a structural design feature of the three-dimensional article. During densification, the open cavity needs to maintain its structure and cannot be filled or blocked. Infiltration into the open cavity allows the ceramic powder to support the geometry of the compacted body during isostatic pressing, thereby ensuring that the structural integrity of the compacted body is not affected. To prevent structural integrity failure, it is preferable that the ceramic powder does not liquefy during isostatic pressing.

[0044] Table 1 shows the characteristics of the load-transfer powder.

[0045]

[0046] In one embodiment, the load-transfer powder has an isostatic compressive strength greater than or equal to 30 MPa, for example, greater than 35 MPa, greater than 40 MPa, or greater than 50 MPa. The modulus of the load-transfer powder can be 200 to 800 GPa, 250 to 750 GPa, or 300 to 600 GPa.

[0047] In one embodiment, isostatic pressing can be performed using a thermosetting rubber containing load-transfer powder. Based on the total weight of the thermosetting rubber, it may contain at least 10% by weight of load-transfer powder. In some embodiments, the thermosetting rubber may contain 10% to 50% by weight of load-transfer powder, for example, 15% to 40% by weight or 20% to 35% by weight.

[0048] The particle size of the load-transfer powder can be larger than the pore size of the first preform. When the particle size of the load-transfer powder is too small, it may be trapped in the pores of the first preform. When using laser powder bed melting, the molten product may contain cracks requiring further densification; therefore, the particle size of the load-transfer powder is preferably not too small to avoid being trapped in the cracks and hindering densification. Furthermore, the particle size of the load-transfer powder can be smaller than the structural features of the compacted body, including open cavities. In one embodiment, the average particle size of the load-transfer powder can be from 5 μm to 1000 μm, for example, 10 μm to 750 μm, 20 μm to 500 μm, or 25 μm to 250 μm. For isostatic pressing, the load-transfer powder can have a spherical, cylindrical, or irregular shape.

[0049] Isostatic pressing can include cold isostatic pressing or hot isostatic pressing. Isostatic pressing can densify complex shapes and achieve a higher degree of densification than uniaxial processes. In one embodiment, the dense article and load-transfer powder can be placed in a closed space, such as an elastomer bag. This closed space is strong enough to maintain its integrity under isostatic pressing without cracking, breaking, or otherwise rupturing, but will deform to transfer the isostatic pressure to the dense article. Preferably, the dense article is embedded in the load-transfer powder within the elastomer bag. The air in the elastomer bag is extracted and sealed. In one embodiment, a vacuum may be applied during sealing to remove air from the elastomer bag. The sealed bag is placed in a container. Pressure is applied using hydrostatic pressure. The pressure can be increased to up to 400 MPa, for example, up to 325 MPa, up to 300 MPa, up to 280 MPa, up to 260 MPa, up to 200 MPa, up to 175 MPa, or up to 150 MPa, within a specified time for compacting the dense article. Argon is typically used as the process gas for applying isostatic pressure, but other working gases may also be used. The isostatic pressure application time can be from 5 to 240 minutes, for example, 10 to 180 minutes, 10 to 120 minutes, or 20 to 120 minutes.

[0050] Cold isostatic pressing can be performed at an ambient temperature of 15°C to 25°C, for example, 20°C to 25°C. Preferably, the cold isostatic pressing process does not require heating. In one embodiment, the pressure range of cold isostatic pressing is 20 to 400 MPa, for example, 25 to 325 MPa, or 75 to 300 MPa.

[0051] When using cold isostatic pressing, the process can employ either a dry bag process or a wet bag process. The wet bag process uses a pressure medium or similar fluid to surround the elastomeric bag, while the dry bag process applies pressure directly to the elastomeric bag. The wet bag process uses a thermoplastic material, which is a waterproof formable bag or mold. In one embodiment, the waterproof formable bag or mold may be made of polyurethane. Both processes allow pressure to be applied evenly around the dense article. Preferably, cold isostatic pressing can use a dry bag process for higher throughput and efficiency.

[0052] Hot isostatic pressing (HIP) can operate at temperatures above ambient, ranging from above 25°C to a maximum of 1200°C, for example, 40°C to 1150°C, 60°C to 1100°C, 100°C to 1050°C, 350°C to 1025°C, or 400°C to 1000°C. In one embodiment, HIP can operate at pressures from 30 MPa to 175 MPa, for example, 30 MPa to 150 MPa, 45 MPa to 125 MPa, or 50 MPa to 110 MPa.

[0053] In hot isostatic pressing (HIP), quenching techniques can be used, such as uniform and rapid cooling at rates up to 100°C / min, for example, up to 80°C / min or 70°C / min. The cooling process can utilize circulating gas to cool the densified product. For HIP, controlled cooling limits grain growth and thermal deformation in the densified product. Furthermore, it reduces surface contamination.

[0054] After isostatic pressing, the densified product can be separated from the load-transfer powder. In some embodiments, at least a portion of the load-transfer powder or a portion thereof remains uncompacted or retains loose characteristics.

[0055] In some implementations, the method may include multiple isostatic pressing steps.

[0056] Sufficient density obtained from additively manufactured articles allows for the production of high-quality articles with good mechanical properties, such as yield strength (0.2% offset), tensile strength, and / or elongation. In one embodiment, the process produces a densified article after sintering and isostatic pressing, with a density greater than or equal to 90% of the theoretical density, for example, greater than 95%, greater than 98%, greater than 99%, or more preferably greater than 99.5% of the theoretical density. In terms of density range, the density of the densified article can be from 90% to 105% of the theoretical density, for example, 90% to 102%, 90% to 101%, 90% to 100.5%, 90% to 100%, 92% to 100%, 93% to 100%, 95% to 100%, or 95% to 99.9% of the theoretical density.

[0057] Implementation Scheme 1 is a method for densification, comprising: depositing metal powder using an additive manufacturing process to form a first preform; sintering the first preform at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in a load-transfer powder in a confined space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article.

[0058] Implementation scheme 2 is the method of implementation scheme 1, wherein the first blank has at least one open cavity.

[0059] Implementation scheme 3 is the method of any one of implementation scheme 1 or 2, wherein the at least one open cavity occupies at least 5% of the volume of the first blank.

[0060] Implementation scheme 4 is the method of any one of implementation schemes 1-3, wherein the additive manufacturing process is a binder spraying process, and wherein the first blank is a green blank.

[0061] Implementation scheme 5 is the method of any one of implementation schemes 1-4, wherein the additive manufacturing process is a laser powder bed melting process, and wherein the first preform is a molten product.

[0062] Implementation scheme 6 is the method of any one of implementation schemes 1-5, wherein the metal powder comprises beryllium.

[0063] Implementation Scheme 7 is the method of any one of Implementation Schemes 1-6, wherein the metal powder contains at least 95% by weight of beryllium, based on the total weight of the metal powder.

[0064] Implementation scheme 8 is the method of any one of implementation schemes 1-7, wherein the metal powder contains less than 1% by weight of cobalt, based on the total weight of the metal powder.

[0065] Implementation scheme 9 is the method of any one of implementation schemes 1-8, wherein the metal powder contains less than 1% by weight of nickel, based on the total weight of the metal powder.

[0066] Implementation scheme 10 is the method of any one of implementation schemes 1-9, wherein at least 50% of the metal powder has an aspect ratio of 2:1 to 1:1.

[0067] Implementation scheme 11 is the method of any one of implementation schemes 1-10, wherein the metal powder has an irregular shape.

[0068] Implementation scheme 12 is the method of any one of implementation schemes 1-11, wherein the average diameter of the metal powder is less than or equal to 45 micrometers.

[0069] Implementation scheme 13 is the method of any one of implementation schemes 1-12, wherein the metal powder has a bimodal distribution.

[0070] Implementation scheme 14 is the method of any one of implementation schemes 1-13, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder of 10:1 to 2:1, preferably 8:1 to 4:1, wherein the average diameter of the coarse metal powder is 50 to 400 micrometers and the average diameter of the fine metal powder is 25 to 40 micrometers.

[0071] Implementation scheme 15 is the method of any one of implementation schemes 1-14, wherein isostatic pressing includes cold isostatic pressing or hot isostatic pressing.

[0072] Implementation scheme 16 is the method of implementation scheme 15, wherein hot isostatic pressing is operated at a temperature of up to 1150°C.

[0073] Implementation scheme 17 is the method of any one of implementation schemes 15 or 16, wherein hot isostatic pressing is operated at a pressure of 60 MPa to 175 MPa.

[0074] Implementation scheme 18 is the method of any one of implementation schemes 1-17, wherein the load transfer powder is ceramic powder.

[0075] Implementation scheme 19 is the method of any one of implementation schemes 1-18, wherein the load transfer powder comprises alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica or a combination thereof.

[0076] Implementation scheme 20 is the method of any one of implementation schemes 1-19, wherein the apparent density of the densified article is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0077] Implementation scheme 21 is a method for densification, comprising: depositing metal powder using an additive manufacturing process to form a green body; sintering the green body at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in load-transfer powder in a confined space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article.

[0078] Implementation scheme 22 is a method of implementation scheme 21, wherein the green body has at least one open cavity.

[0079] Implementation scheme 23 is the method of any one of implementation schemes 21 or 22, wherein the at least one open cavity occupies at least 5% of the green body volume.

[0080] Implementation scheme 24 is the method of any one of implementation schemes 21-23, wherein the additive manufacturing process is a binder spraying process.

[0081] Implementation scheme 25 is the method of any one of implementation schemes 21-24, wherein the metal powder comprises beryllium.

[0082] Embodiment 26 is the method of any one of Embodiments 21-25, wherein the metal powder contains at least 95% by weight of beryllium, based on the total weight of the metal powder.

[0083] Implementation scheme 27 is the method of any one of implementation schemes 21-26, wherein the metal powder contains less than 1% by weight of cobalt, based on the total weight of the metal powder.

[0084] Implementation scheme 28 is the method of any one of implementation schemes 21-27, wherein the metal powder contains less than 1% by weight of nickel, based on the total weight of the metal powder.

[0085] Implementation scheme 29 is any one of implementation schemes 21-28, wherein at least 50% of the metal powder has an aspect ratio of 2:1 to 1:1.

[0086] Implementation scheme 30 is the method of any one of implementation schemes 21-29, wherein the metal powder has an irregular shape.

[0087] Implementation scheme 31 is the method of any one of implementation schemes 21-30, wherein the average diameter of the metal powder is less than or equal to 45 micrometers.

[0088] Implementation scheme 32 is the method of any one of implementation schemes 21-31, wherein the metal powder has a bimodal distribution.

[0089] Implementation scheme 33 is the method of any one of implementation schemes 21-32, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder of 10:1 to 2:1, preferably 8:1 to 4:1, wherein the average diameter of the coarse metal powder is 50 to 400 micrometers, and the average diameter of the fine metal powder is 25 to 40 micrometers.

[0090] Implementation scheme 34 is the method of any one of implementation schemes 21-33, wherein isostatic pressing includes cold isostatic pressing or hot isostatic pressing.

[0091] Implementation scheme 35 is the method of implementation scheme 34, wherein hot isostatic pressing is operated at a temperature of up to 1150°C.

[0092] Implementation scheme 36 is the method of any one of implementation schemes 34 or 35, wherein hot isostatic pressing is operated at a pressure of 60 MPa to 175 MPa.

[0093] Implementation scheme 37 is the method of any one of implementation schemes 21-36, wherein the load transfer powder is ceramic powder.

[0094] Implementation scheme 38 is the method of any one of implementation schemes 21-37, wherein the load transfer powder comprises alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica or a combination thereof.

[0095] Implementation scheme 39 is a method of any of the implementation schemes 21-38, wherein the apparent density of the densified article is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0096] Implementation scheme 40 is a method for densification, comprising: depositing metal powder using an additive manufacturing process to form a molten article; sintering the molten article at a temperature of 825°C to 1275°C in a reducing or inert atmosphere to form a dense body; encapsulating the dense body in a load-transfer powder in a confined space; and isostatically pressing the dense body and the load-transfer powder to provide a densified article.

[0097] Implementation scheme 41 is the method of implementation scheme 40, wherein the molten article has at least one open cavity.

[0098] Implementation scheme 42 is the method of any one of implementation schemes 40 or 41, wherein the at least one opening occupies at least 5% of the volume of the first blank.

[0099] Implementation scheme 43 is the method of any one of implementation schemes 40-42, wherein the additive manufacturing process is a laser powder bed melting process.

[0100] Implementation scheme 44 is the method of any one of implementation schemes 40-43, wherein the metal powder comprises beryllium.

[0101] Embodiment 45 is the method of any one of Embodiments 40-44, wherein the metal powder contains at least 95% by weight of beryllium, based on the total weight of the metal powder.

[0102] Implementation scheme 46 is the method of any one of implementation schemes 40-45, wherein the metal powder contains less than 1% by weight of cobalt, based on the total weight of the metal powder.

[0103] Implementation scheme 47 is the method of any one of implementation schemes 40-46, wherein the metal powder contains less than 1% by weight of nickel, based on the total weight of the metal powder.

[0104] Implementation scheme 48 is the method of any one of implementation schemes 40-47, wherein at least 50% of the metal powder has an aspect ratio of 2:1 to 1:1.

[0105] Implementation scheme 49 is the method of any one of implementation schemes 40-48, wherein the metal powder has an irregular morphology.

[0106] Implementation scheme 50 is the method of any one of implementation schemes 40-49, wherein the average diameter of the metal powder is less than or equal to 45 micrometers.

[0107] Implementation scheme 51 is the method of any one of implementation schemes 40-50, wherein the metal powder has a bimodal distribution.

[0108] Implementation scheme 52 is the method of any one of implementation schemes 40-51, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder of 10:1 to 2:1, preferably 8:1 to 4:1, wherein the average diameter of the coarse metal powder is 50 to 400 micrometers and the average diameter of the fine metal powder is 25 to 40 micrometers.

[0109] Implementation scheme 53 is the method of any one of implementation schemes 40-52, wherein isostatic pressing includes cold isostatic pressing or hot isostatic pressing.

[0110] Implementation scheme 54 is the method of implementation scheme 53, wherein hot isostatic pressing is operated at a temperature of up to 1150°C.

[0111] Implementation scheme 55 is the method of any one of implementation schemes 53 or 54, wherein hot isostatic pressing is operated at a pressure of 60 MPa to 175 MPa.

[0112] Implementation scheme 56 is a method of any of the implementation schemes 40-55, wherein the load transfer powder is ceramic powder.

[0113] Implementation scheme 57 is a method of any of the implementation schemes 40-56, wherein the load transfer powder comprises alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica or a combination thereof.

[0114] Implementation scheme 58 is a method of any of the implementation schemes 40-57, wherein the apparent density of the densified article is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0115] This disclosure has been described with reference to exemplary embodiments. It is obvious that others may make modifications and alterations upon reading and understanding the above detailed description. This disclosure is intended to be construed as including all such modifications and alterations, provided they fall within the scope of the appended claims or their equivalents. In one embodiment, any or part of the steps or components disclosed herein may be considered optional. In some cases, any or part of the foregoing items in this specification may be explicitly excluded, for example, by the language of the claims. For example, the language of the claims may be modified to describe other process steps.

[0116] The following non-limiting examples help to further understand the contents of this disclosure.

[0117] Example

[0118] A binder-jet additive manufacturing process was used, employing beryllium powder to form cylinders. The cylinder density was greater than 65%. Example 1 was sintered at 1220°C, and Example 2 at 1270°C. After sintering, the cylinders were placed in a sealed container, wrapped with alumina, and then vacuum-evacuated and sealed. The sealed cylinders were then subjected to hot isostatic pressing (HIP) at 1000°C and 103.4 MPa (15 ksi). The cylinders were removed from the HIP sealed container and de-powdered. Six specimens were tested for each example, and the average values ​​are listed in Table 2. The 0.2% offset yield strength and ultimate tensile strength were determined according to ASTM E8. Elongation % was determined according to ASTM E3. The theoretical density of beryllium is 1.85 g / cc.

[0119]

[0120] Samples from each embodiment were tested to determine the weight percentages of carbon and oxygen. The weight percentage of BeO was calculated by multiplying the weight percentage of O by 1.5633. Based on these calculations, the weight percentage of BeO was determined to be below 1.5 wt%, which is below the target level of 2.0 wt%. The composition is shown in Table 3.

[0121]

[0122] While the present invention has been described in detail, those skilled in the art will understand that modifications can be made to the invention without departing from its spirit and scope. In light of the foregoing discussion, knowledge of the relevant technical fields and the references relating to the background and detailed description above are incorporated herein by reference. Furthermore, it should be understood that various aspects of the invention, as well as portions and features of the various embodiments described below and / or in the appended claims, can be combined or interchanged in whole or in part. In the foregoing description of various embodiments, references to other embodiments may be appropriately combined with other embodiments, as will be understood by those skilled in the art. Moreover, those skilled in the art should understand that the foregoing description is merely illustrative and not intended to limit the invention.

Claims

1. A method for densification, comprising: Metal powder is deposited using an additive manufacturing process to form a first preform; The first blank is sintered in a reducing or inert atmosphere at a temperature of 825°C to 1275°C to form a dense body. Within a confined space, the dense body is encapsulated in load-transfer powder; as well as The dense body and the load-transfer powder are subjected to isostatic pressing to provide a densified article.

2. The method according to claim 1, wherein the first blank has at least one open cavity.

3. The method according to claim 2, wherein the at least one open cavity occupies at least 5% of the volume of the first blank.

4. The method according to any one of claims 1-3, wherein the metal powder comprises beryllium.

5. The method according to any one of claims 1-4, wherein the metal powder comprises at least 95% by weight of beryllium, based on the total weight of the metal powder.

6. The method according to any one of claims 1-5, wherein the metal powder contains less than 1% by weight of cobalt, based on the total weight of the metal powder, or wherein the metal powder contains less than 1% by weight of nickel, based on the total weight of the metal powder.

7. The method according to any one of claims 1-6, wherein at least 50% of the metal powder has an aspect ratio of 2:1 to 1:

1.

8. The method according to any one of claims 1-7, wherein the average diameter of the metal powder is less than or equal to 45 micrometers.

9. The method according to any one of claims 1-8, wherein the metal powder has a bimodal distribution.

10. The method according to any one of claims 1-9, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder of 10:1 to 2:1, preferably 8:1 to 4:1, wherein the average diameter of the coarse metal powder is 50 to 400 micrometers, and the average diameter of the fine metal powder is 25 to 40 micrometers.

11. The method according to any one of claims 1-10, wherein the isostatic pressing includes cold isostatic pressing or hot isostatic pressing.

12. The method according to any one of claims 1-11, wherein the load transfer powder comprises alumina, silicon carbide, zirconium oxide, titanium dioxide, fused silica, or a combination thereof.

13. The method according to any one of claims 1-12, wherein the apparent density of the densified article is greater than 90% of the theoretical density, more preferably greater than 99.5%.

14. The method according to any one of claims 1-13, wherein the additive manufacturing process is a binder spraying process, and wherein the first blank is a green blank.

15. The method according to any one of claims 1-13, wherein the additive manufacturing process is a laser powder bed melting process, and wherein the first preform is a molten product.

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