Methods for producing a densified article

Abstract

Methods are described for densifying articles produced from additive manufacturing processes, such as binder jet processes and laser powder bed fusion processes. The method may be used to make articles that comprise beryllium. The article may have an open cavity, a designed internal structural feature. In one embodiment, the method uses a sinter step prior to isostatic pressing.

Description

Methods for Producing A Densified ArticlePRIORITY CLAIM

[0001] The application claims priority to U.S. Provisional Application No. 63 / 516,978 filed on August 1 , 2023, which is fully incorporated by reference herein.TECHNICAL FIELD

[0002] The present disclosure relates to a method for producing a densified article from an additive manufacturing process. In particular the present disclosure relates to producing articles from a binder jet additive manufacturing process and densifyingthe article by sintering prior to subjecting to an isostatic pressing with a load transmitting powder.BACKGROUND

[0003] Additive manufacturing is a set of advanced manufacturing technologies which enable the production of complex shapes through the addition of material layer-upon- layer. This is a departure from conventional subtractive manufacturing, forming and other traditional approaches for manufacturing components. Additive manufacturing is a production technology for the rapid and flexible production of components including prototype parts, end-use parts, and tooling. By building in layer-upon-layer approach, additive manufacturing has design freedom to produce three-dimensional (3D) articles using computer-aided design (CAD) modeling software. Building in this manner allows manufacturers to design geometries, internal features and other structures which would be challenging or impossible to form using traditional subtractive techniques.

[0004] A digital blueprint of a desired solid object is created and then that virtual blueprint is divided into digital cross-sections / layers. Each layer begins with a thin distribution of metal powder spread over the surface of a bed or platform. The metal powder may be selectively joined where the object is to be formed. A piston that supportsthe bed / platform within a build box lowers so that the next powder layer can be spread and selectively joined. This sequential layering process repeats to build up the desired part. Following heat treatment, unbound powder is removed, leavingthe semi-fabricated part.

[0005] Additive manufacturing has many advantages, including dramatically reducing the time from design to prototyping to commercial product. Demonstration units and parts can be rapidly produced. Parts can be created of any geometry, and generally out of ceramics, metals, polymers, and composites. Local control can be exercised over the material composition, microstructure, and surface texture. Running design changes are possible. Multiple parts can be built in a single assembly. No complicated potentially onetime die ortooling needs to be made before a prototype can be produced. Minimal energy is needed to make these 3D solid objects. It also decreases the amount of waste and raw materials. Additive manufacturing also facilitates production of extremely complex geometrical parts. Support material can be used to create overhangs, undercuts, and internal volumes. Additive manufacturing also reduces the parts inventory for a business since parts can be quickly made on-demand and on-site.

[0006] Additive manufacturing methods include electron beam melting and sintering, laser melting and sintering. Both electron beam and laser methods can be used to sinter or fuse the given cross-section to the layer underneath. In electron beam melting, after the deposition of metal powder, the loose metal powder cross-section is melted or fused by an electron beam. In laser sintering, a laser beam is used to sinter areas of the loosely compacted metal powder cross-section. The term “sintering” refers to the process by which particulates adhere into a solid mass due to externally applied energy. Laser sintering will also fuse a given cross-section with the already-sintered cross-section beneath. The metal powderthat is not struck by the laser beam remains loose and falls away from the finished part when removed from the build bed. Alternatively, the finished part can be depowdered by vacuuming or using a fluid such as compressed air to wash the finished part and dislodge any loose powder. Subsequent finishing steps may also be applied to the part to produce the desired characteristics. Such steps include, but are not limited to, further curing, sintering, infiltration, annealing, and final surface finishing.

[0007] Another manufacturing method includes binder jetting. In binder jetting, after the deposition of metal powder, a liquid binding agent is selectively deposited to bond powder particles together. The finished part is developed through the layering of powder and binder. Binder jetting may result in a green finished part. The term “green part” or “green body” refers to articles or preforms which are produced to be further processed with other manufacturing techniques. For example, metal green parts may be further processed by sintering in an oven or infiltrated with at least one metal. The infiltration fills voids within the sintered preform.

[0008] US Pat. No. 11 ,400,516 describes a method for producing a three-dimensional model via additive manufacturing. The method includes building a green block in a layerwise manner with a powder material, e.g. aluminum alloy, and a solidifiable nonpowder material. The green block includes a green usable model. The solidified nonpowder material is removed from the green block to extract the green usable model from the green block and the density of the green usable model is increased by applying cold isostatic pressing (CIP). The green usable model is then sintered to produce a three- dimensional model.

[0009] US Pub. No. 2023 / 0059163 describes additive manufacture techniques that enable the densification of green articles prior to further article processing. The method of forming an article comprises providing a powder composition, and forming the powder composition into a green article by one or more additive manufacturing techniques. The green article is contacted with a powder pressure transfer media. The green article and powder pressure transfer media are then subjected to cold isostatic pressing (CIP) or warm isostatic pressing (WIP) at a pressure less than minimum isostatic compaction pressure of the powder pressure transfer media to provide a densified green article.

[0010] There still remains a need for producing high quality articles from an additive manufacturing process.SUMMARY

[0011] The methods described herein are for densifying articles, such as green bodies orfused articles, producing by an additive manufacturing process priorto further processing. In general the method uses the additive manufacturing process to build a complex article and then uses an isostatic pressing to increase the density of the article. The produced article has improvements in mechanical properties.

[0012] In one aspect there is provided a method for densifying comprising depositing metal powder to form a first body using an additive manufacturing process; sintering the first body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surroundingthe dense body in a load transmitting powderwithin an enclosure; and subjecting the dense body and the load transmitting powder to isostatic pressing to provide a densified article. In one embodiment, the first body has an open cavity, which is a designed structural feature that is internal within the first body. In some embodiments, the first body may have more than one open cavities. Preferably, the open cavity comprises at least 5% of the volume of the first body. The densified article may have an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0013] The metal powder may comprise beryllium. In one embodiment, the metal powder comprises at least 95% by weight of beryllium based on the total weight of the metal powder. The metal powder comprises 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 cylinder morphology, but the powder may also have an irregular morphology. In one embodiment, at least 50% of the metal powder have an aspect ratio of 2:1 to 1 :1 . In one embodiment, the metal powder has an average diameter of less than or equal to 45 microns. Bimodal powder may also be used. In one embodiment, the metal powder has a bimodal distribution having a ratio of coarse metal powder to fine metal powder from 10:1 to 2:1 , preferably from 8:1 to 4:1 , wherein the coarse metal has an average diameter from 50 to 400 microns, and the fine metal powder has an average diameter from 25 to 40 microns.

[0014] In one embodiment, the isostatic pressing comprises cold isostatic pressing or hot isostatic pressing. The hot isostatic pressing may operate at a temperature up to 1150°C. and pressures rangingfrom 30 MPa to 175 MPa. Priorto the isostatic pressing, the load transmitting powder is used to surround the first body. The load transmitting powder may be a ceramic powder. In one embodiment, the load transmitting powder comprises alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof.

[0015] In one aspect there is provided a method for densifying comprising depositing metal powder to form a green body using an additive manufacturing process, preferably a binder jet process; sintering the green body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surrounding the dense body in a load transmitting powder within an enclosure; and subjecting the dense body and the load transmitting powderto isostatic pressingto provide a densified article. In one embodiment, the green body has an open cavity, which is a designed structural feature that is internal within the green body. In some embodiments, the green body may have more than one open cavities. The densified article may have an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0016] In one aspect there is provided a method for densifying comprising depositing metal powder to form a fused article using an additive manufacturing process, preferably a laser powder bed fusion process; sintering the fused article at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surroundingthe dense body in a load transmitting powder within an enclosure; and subjectingthe dense body and the load transmitting powder to isostatic pressingto provide a densified article. In one embodiment, the fused article has an open cavity, which is a designed structural feature that is internal within the fused article. In some embodiments, the fused article may have more than one open cavities. The densified article may have an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0017] These and other non-limiting characteristics are more particularly described below.DETAILED DESCRIPTION

[0018] The present invention may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein. Elements, apparatus and methods described herein, however, are not limited to the specific embodiments presented in the detailed description and examples. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations will be readily apparent to those of skill in the art without departing from the spirit and scope of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0020] The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0021] As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” The terms “comprise(s)”, “include(s)”, “having”, “has”, “can”, “contain(s)”, and variants thereof, as used herein, are intended to be open-ended transitional phrases that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps.However, such description should be construed as also describing compositions or methods as “consisting of” and “consisting essentially of” the enumerated ingredients / steps, which allows the presence of only the named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0022] Numerical values in the specification and claims of this application, as they relate to polymers or polymer compositions, reflect average values for a composition that may contain individual polymers of different characteristics. The numerical values disclosed herein should be understood to include numerical values which are the same when reduced to the same number of significant FIGURES and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0023] All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 1 micron to 40 microns” is inclusive of the endpoints, 1 micron and 40 microns, and all the intermediate values). The endpoints of the ranges and any values disclosed herein are not limited to the precise range orvalue; they are sufficiently imprecise to include values approximatingthese ranges and / orvalues.

[0024] As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, may not be limited to the precise value specified, in some cases. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4”. The term “about” may referto plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11 %, and “about 1 ” may mean from 0.9-1 .1 .

[0025] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 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 contemplated.

[0026] The embodiments described herein provide a method of densifying an article comprising providing a metal powder to form a first body using additive manufacturing techniques. In one embodiment, the first body may be a green body when using a binder jet process and a fused article for a laser powder bed fusion process. For purposes of the present disclosure the method uses a sintering process after the additive manufacturing but prior to the isostatic pressing. After sintering the method comprises surrounding the dense body in a load transmitting powder and then subjecting both the dense body and the load transmitting powder to isostatic pressing. Accordingly, the method is efficient in producing densified articles from additive manufacturing processes.

[0027] The method described herein using additive manufacturing techniques that builds a three-dimensional article using a layer-by-layer approach. There are several additive manufacturing techniques available to form the first body, including VAT photopolymerization, material jetting, binding jetting, material extrusion, powder bed fusion, sheet lamination or directed energy deposition. Powder bed fusion includes direct metal laser sintering, electron beam melting, selective heat sintering, selective laser melting and selective laser sintering. In one embodiment, the method uses an additive manufacturing techniques that employs a powder bed, such as binding jetting or powder bed fusion. For purposes of the present disclosure, the additive manufacturing process will be described in terms of binding jetting or laser power bed fusion, but it should be understood that other additive manufacturing techniques may be used.

[0028] As with additive manufacturing process, the method begins with constructing 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 the binder jetting process, the sliced layers detail the design parameters of the part to be formed includingthe open cavity. The binder jetting apparatus spreads a layer of the powder composition in a build box. Any suitable technique to deposit the initial layer may be used, including spreading, coating, brushing, rolling, spraying, or dispensing. The deposited layer may be a thin layer of powder. After each layer is deposited a jetted fluid, referred to as a binder, is selectively applied by aprinting mechanism to the build surface accordin the model. The build surface refers to the upper most surface in the build box at any particular time. After depositing the binder, the build box is moved and another layer of the powder is deposited. In most processes it is convenient to lower the build box. The process repeats until the first body or green body is formed according to the model. In some embodiments, the process may involve drying between depositing each layer. Overall the binder jetting process does not require heat and is a cold process, which prevents introducing stress to the article. In addition, the article beingformed is supported duringthe process due to the surrounding powder in the build box. Prior to removing the first body from the build box, the process may use a curing step to activate the binder. The loose powder may be removed to obtain the first body.

[0029] In one embodiment, the first body has at least one open cavity, such as the interior cavities, such as crevices, channels, orifices, recesses, or other hollow areas. This open cavity is a structural design feature for the article that is different from a void, pore or crack. The open cavity is not filled or densified, while the void, pore or crack becomes densified duringthe method. Accordingly, duringthe densification, the open cavity is preferably maintained without being blocked, filled in or otherwise structurally compromised. In one embodiment, at least 5% of the volume of the article may be an open cavity, e.g., at least 10% of the volume, at least 15% of the volume, at least 20% of the volume, or at least 25% of the volume. Preferably, the open cavity is internal.

[0030] For binder jet processes, the binderthat may be used in the process includes 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, polyolefins, 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 may be curable at low temperature, such as for example from 90°C to 140°C, e.g. from 105°C to 130°C, or from 110°C to 125°C. The curingtime may vary as needed but is preferably cured in less than 6 hours, e.g., less than 5 hours or less than 4 hours. No binder is used for laser powder bed fusion.

[0031] In one embodiment, the metal powder comprises beryllium. The metal powder may comprises at least 95% by weight of beryllium based on the total weight of the metal powder, e.g., 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 ranges the metal powder may comprise from 95% by weight to 100% by weight of beryllium based on the total weight of the metal powder, e.g., from 95% by weight to 99.9% by weight of beryllium, from 96% by weight to 99.5% by weight of beryllium or from 97% by weight to 99% by weight of beryllium. The metal powder may comprise other metals, but it is more preferred to use high purity beryllium. In one embodiment, the metal powder comprises less than or equal to 1 % by weight of cobalt based on the total weight of the metal powder, e.g., 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 comprises less than or equal to 1 % by weight of nickel based on the total weight of the metal powder, e.g., 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 that may be present that preferably do not exceed the weight percentage of cobalt or nickel respectively. The composition of the metal powder preferably behaves homogenous when deposited in the build box to prevent segregation of particles that lead to inconsistent results.

[0032] The metal powder may have a morphology that is irregular, polygonal, spherical, or combination thereof. Morphology may be determined by SEM images. In one embodiment, at least 50% of the metal powder have an aspect ratio of 2:1 to 1 :1 , e.g., at least 60% of the metal powder have an aspect ratio of 2:1 to 1 :1 or at least 75% of the metal powder have an aspect ratio of 2:1 to 1 :1 .

[0033] In some embodiments, the metal powder exhibits a Gaussian particle size distribution. The metal powder, which preferably comprises beryllium, may have an average (d50) diameter of less than or equal to 45 microns, e.g., less than or equal to 40microns, less than or equal to 35 microns, less than or equal to 30 microns, less than or equal to 25 microns or less than or equal to 20 microns. In terms of ranges, the metal powder may have an average (d50) diameter from 1 to 45 microns, e.g., from 1 to 40 microns, from 5 to 40 microns, from 5 to 35 microns, from 5 to 30 microns or from 10 to 25 microns. The size of the metal powder allows the metal powder to be deposited in adequate manner in the build box. Particle distribution corresponding to 50% in the cumulative distribution curve is referred to as the average particle size.

[0034] In other embodiments, the metal powder may have a bimodal distribution. A bimodal distribution may have a ratio of coarse particles to fine particles. Coarse particles may have an average (d50) diameter of greater than or equal to 50 microns, e.g., greater than or equal to 55 microns, greater than or equal to 60 microns or greater than or equal to 75 microns. In terms of ranges the coarse particles may have average (d50) diameter from 50 to 400 microns, e.g., from 50 to 300 microns, or from 75 to 150 microns. Fine particles may have an average (d50) diameter of less than or equal to 40 microns, e.g., less than or equal to 30 microns, less than or equal to 25 microns or less than or equal to 10 microns. Fine particles may have an average (d50) diameter rangingfrom 0.01 to 40 microns, e.g., from 0.5 to 40 microns, from 1 to 40 microns, from 1 to 35 microns, from 5 to 35 microns, orfrom 20 to 35 microns. One preferred range for fine particles may be from 25 to 40 microns, e.g., from 30 to 40 microns or from 30 to 35 microns. The fine particles may be on the nano scale and may be less than 1 microns in some embodiments. Accordingly, the nano scale fine particles may be from 1 nm to 950 nm, e.g., from 10 nm to 700 nm or from 50 nm to 550 nm. The ratio of coarse particles to fine particles in a bimodal distribution may be from 10:1 to 2:1 , e.g., from 8:1 to 3:1 , from 8:1 to 4:1 , orfrom 6:1 to 4:1 . The coarse and fine particles may have similar morphology, i.e. both spherical, or different morphologies including different aspect ratios.

[0035] The metal powder has an apparent density that may be greater than 50% of the theoretical density of the metal powder, e.g., greater than 60%, greater than 70%, or greaterthan 80%. The apparent density may be assessed usingthe Carney funnelaccordingto the ASTM Standard B417 (Standard Test Method for Apparent Density of Non- Free-Flowing Metal Powders Using the Carney Funnel).

[0036] In addition to the apparent density of the metal powder, the metal powder also has a tap density. In one embodiment, the tap density may be greater than 60% of the theoretical density of the metal powder, e.g., greater than 65%, greater than 70%, or greater than 80%. Tap density may be measured using a graduated cylinder as described by ASTM Standard B527 (“Standard Test Method forTapped Density of Metal Powders and Compound.”). The measurement may be obtained by mechanically tapping until little further volume change is observed. Tapped density may be calculated as the mass divided by the final volume of the metal powder.

[0037] In one embodiment, the method comprises depositing metal powder, contactingthe metal powerwith a binder, curingthe binder, and removingthe first body from the loose metal powder. The loose metal powder may be reprocessed as needed. The method may further comprise sintering the first body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body. In one embodiment, the heat treatment may be sintered at a temperature from 850°C to 1250°C, e.g., from 900°C to 1150°C, from 900°C to 1125°C, or from 925°C to 1050°C. During the sintering, the temperature is increased to sufficiently volatilize, decompose or otherwise remove most of the binder from the first body. Preferably for binder jetting, the first body (green body) contains less than or equal to 2.0% by weight of binder after the sinter based on the weight of the first body, e.g. less than 1 .5% by weight or less than 1 .0% by weight. In some embodiments, the sintering is sufficient to remove all of the binder from the green body. The amount of binder remaining after sinter is preferably low enough to not effect the mechanical properties of the densified article.

[0038] Other processes have used a sintering step after the isostatic pressing. The present embodiments have found the sintering before isostatic pressing improves the production of the dense articles.

[0039] The sintering step may result in a size reduction of the first body. Although this may be accounted and predicted in the model, it is preferred to control the reduction in the sintering step to prevent excessive size reduction. In one embodiment, the sintering is carried out for a sufficient time such that the first body is reduced in size by no more than 20% of volume, based on the volume of the first body. Preferably, the size reduction is no more than 15% of volume, or no more than 10% of volume, or no more than 5% of volume.

[0040] In one embodiment, the sintering temperature is raised above the solidus temperature and below the and liquid temperature of the metal powder comprising beryllium. This promotes the beryllium particles to fuse together through metallic bonds. The time required for heating the first body may vary based on the selected sintering temperatures as well as the size and geometry of the first body. The sintering time is sufficient to achieve at least 70% theoretical density, and preferably from 70% to 90% theoretical density, or more preferably from 70 to 80% theoretical density. Additional densification may be achieved by the isostatic pressing in the subsequent steps.

[0041] In one embodiment, the method comprises an isostatic pressingto achieve a densified article. The densified article after isostatic pressing possesses a theoretical density that is greater than the theoretical density after sintering. By usingthe isostatic pressing the embodiments may be able to achieve a densified article that has a reduced presence of internal defects, includingvoids. Under some conditions this may allow the residual porosity to be significantly reduced or eliminated. In particular, the method may include surrounding the dense body in a load transmitting powder within an enclosure, and subjectingthe dense body and the load transmitting powder to isostatic pressingto provide a densified article. The dense body may be fully surrounded by the load transmitting powder such that the load transmitting powder is in direct contact with the dense body.

[0042] In one embodiment, the load transmitting powder is a ceramic powder. The ceramic powder may include alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof. In a preferred embodiment, the load transmitting powder isalumina. The ceramic powder may be a loose powder. In one embodiment, the ceramic powder may penetrate into the structural features of the dense body including at least one open cavity, such as the interior cavities, such as crevices, channels, orifices, recesses, or other hollow areas. The open cavity is structurally designed feature for the 3D article. When densifying the open cavities need to maintain the structure without being filled or blocked. Penetrating into the open cavity allows the ceramic powderto support the geometry of the dense body during the isostatic pressing so that the structural integrity of the dense body is not compromised. To prevent a failure in structural integrity it is preferred that the ceramic powder does not liquify during the isostatic pressing.

[0043] Table 1 provides the properties of the load transmitting powder.Table 1Ceramic Density, g / cc Sinter Temp °CAl2O33.72 1500-1800ZrO25.68 1300-1650TiO24.23 800Fused SiO22.2 1000-1300SiC 3.21 1950-2180

[0044] In one embodiment, the load transmitting powder has an isostatic compaction pressure that is greater than or equal to 30 MPa, e.g., greater than 35 MPa, greater than 40 MPa, or greater than 50 MPa. The modulus of the load transmitting powder may be from 200 to 800 GPa, from 250 to 750 GPa, or from 300 to 600 GPa.

[0045] In one embodiment, the isostatic pressing may use a thermoset rubber comprising the load transmitting powder. The thermoset rubber may contain at least 10% by weight of the load transmitting powder, based on the total weight of the thermoset rubber. In some embodiments, the thermoset rubber may contain from 10% by weight to 50% by weight of the load transmitting powder, e.g., from 15% by weight to 40% by weight or from 20% by weight to 35% by weight.

[0046] The Load transmitting powder may have a particle size that is greater than the pore size of the first body. When the load transmitting powder has a particle size that is too small the load transmitting powder may become trapped within the pores of the first body. When using laser powder bed fusion processes the fused article may have cracks that require further densification and the load transmitting powder is preferably not too small to become trapped within the crack and prevent densification. In addition, the load transmitting powder may have a particle size that is smaller than the structural features of the dense body includingthe open cavities. In one embodiment, the load transmitting powder may have an average particle size from 5 pm to 1000 pm, e.g., from 10 pm to 750 pm, from 20 pm to 500 pm, or from 25 pm to 250 pm. For purposes of the isostatic pressing, the load transmitting powder may have a spherical, cylindrical, or irregular morphology.

[0047] The isostatic pressing may comprise a cold isostatic pressing or hot isostatic pressing. Isostatic pressing can densify complex shapes and allows for a higher degree of densification that uniaxial processes. In one embodiment, the dense article and load transmitting powder may be placed within an enclosure, such as an elastomeric bag. The enclosure is strong enough to maintain its integrity under the isostatic pressure without splitting, fracturing, or otherwise rupturing, but deforms to transfer the isostatic pressure to the dense article. Preferably, the dense article is buried within the load transmitting powder in the elastomeric bag. Air is evacuated from the elastomeric bag and sealed. In one embodiment, a vacuum may be applied to remove air from the elastomeric bag when sealing. The sealed bag is placed in a vessel. Pressure is applied using hydrostatic pressure. During the defined duration to compact the dense article, the pressure may be increased to up to 400 MPa, e.g., 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. The process gas for applying isostatic pressure is typically argon, although another working gas may be used. The time period for the isostatic pressing may be from 5 to 240 minutes, e.g., from 10 to 180 minutes, from 10 to 120 minutes, orfrom 20 to 120 minutes.

[0048] Cold isostatic pressing may operate with ambient temperatures ranging from 15°C to 25°C, e.g., from 20°C to 25°C. Preferably the cold isostatic pressing is done without adding heat to the process. In one embodiment, the cold isostatic pressing may operate at a pressure from 20 to 400 MPa, e.g., from 25 to 325 MPa, or from 75 to 300 MPa.

[0049] When a cold isostatic pressing is used, the process may use either a dry-bag or wet-bag process. The wet bag process uses a pressure medium or similar fluid that surrounds the elastomeric bag, while the dry-bag process applies the pressure to the elastomeric bag. The wet bag process uses a thermoplastic that is an impervious moldable bag or mold. In one embodiment, the impervious moldable bag or mold may be made of a polyurethane. In both process pressure may be uniformly applied around the dense article. Preferably, the process may use a dry-bag process for the cold isostatic pressing which may achieve higher production and efficiency.

[0050] The hot isostatic pressing may operate with temperatures greater than ambient, and may range from greater than 25°C to up to 1200°C, e.g., from 40°C to 1150°C, from 60°C to 1100°C, from 100°C to 1050°C, from 350°C to 1025°C, or from 400°C to 1000°C. In one embodiment, the hot isostatic pressing may operate at a pressure from 30 MPa to 175 MPa, e.g., from 30 to 150 MPa, 45 to 125 MPa, or from 50 to 110 MPa.

[0051] In the hot isostatic pressing process, the process may use a quenching technique such as uniform rapid coolingthat can provide cooling up to 100°C / min., e.g., up to 80°C / min. or up to 70°C / min. The cooling may involve circulating a gas to cool the densified article. Forthe hot isostatic process, the controlled cooling may restricts grain growth and thermal distortion of the densified article. In addition, surface contamination may be reduced.

[0052] Afterthe isostatic pressing, the densified article can be separated from the load transmitting powder. In some embodiments, at least a portion of the load transmitting powder or a portion thereof remains uncompacted, or retains a loose characteristic.

[0053] In some embodiments, the method may include applying multiple isostatic pressing steps.

[0054] Obtaining sufficient density from additively manufactured articles may result in articles with high quality and good mechanical properties in terms of 0.2% offset yield strength, ultimate tensile strength and / or elongation. In one embodiment, the process produce densified articles after sintering and isostatic pressingthat may be greater than or equal to 90% theoretical density, e.g., greater than 95% theoretical density, greater than 98% theoretical density, greater than 99% theoretical density, or more preferably greater than 99.5% theoretical density. In terms of ranges the densified articles may be from 90% to 105% theoretical density, e.g., from 90% to 102% theoretical density, from 90% to 101% theoretical density, from 90% to 100.5% theoretical density, from 90% to 100% theoretical density, from 92% to 100% theoretical density, from 93% to 100% theoretical density, from 95% to 100% theoretical density, or from 95% to 99.9% theoretical density.

[0055] Embodiment 1 is a method for densifying comprising depositing metal powder to form a first body using an additive manufacturing process; sinteringthe first body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surrounding the dense body in a load transmitting powderwithin an enclosure; and subjecting the dense body and the load transmitting powder to isostatic pressingto provide a densified article.

[0056] Embodiment 2 is a method of embodiment 1 , wherein the first body has at least one open cavity.

[0057] Embodiment 3 is a method of any one of embodiments 1 or 2, wherein the at least one open cavity comprises at least 5% of the volume of the first body.

[0058] Embodiment 4 is a method of any one of embodiments 1-3, wherein the additive manufacturing process is a binder jet process, and wherein the first body is a green body.

[0059] Embodiment 5 is a method of any one of embodiments 1-4, wherein the additive manufacturing process is a laser powder bed fusion process, and wherein the first body is a fused article.

[0060] Embodiment 6 is a method of any one of embodiments 1-5, wherein the metal powder comprises beryllium.

[0061] Embodiment 7 is a method of any one of embodiments 1-6, wherein the metal powder comprises at least 95% by weight of beryllium based on the total weight of the metal powder.

[0062] Embodiment 8 is a method of any one of embodiments 1-7, wherein the metal powder comprises less than 1 % by weight of cobalt based on the total weight of the metal powder.

[0063] Embodiment 9 is a method of any one of embodiments 1-8, wherein the metal powder comprises less than 1 % by weight of nickel based on the total weight of the metal powder.

[0064] Embodiment 10 is a method of any one of embodiments 1 -9, wherein at least 50% of the metal powder have an aspect ratio of 2:1 to 1 :1 .

[0065] Embodiment 11 is a method of any one of embodiments 1 -10, wherein the metal powder has an irregular morphology.

[0066] Embodiment 12 is a method of any one of embodiments 1 -11 , wherein the metal powder has an average diameter of less than or equal to 45 microns.

[0067] Embodiment 13 is a method of any one of embodiments 1 -12, wherein the metal powder has a bimodal distribution.

[0068] Embodiment 14 is a method of any one of embodiments 1 -13, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder from 10:1 to 2:1 , preferably from 8:1 to 4:1 , wherein the coarse metal has an average diameter from 50 to 400 microns, and the fine metal powder has an average diameter from 25 to 40 microns.

[0069] Embodiment 15 is a method of any one of embodiments 1 -14, wherein the isostatic pressing comprises cold isostatic pressing or hot isostatic pressing.

[0070] Embodiment 16 is a method of embodiments 15, wherein the hot isostatic pressing operates at a temperature up to 1150°C.

[0071] Embodiment 17 is a method of any one of embodiments 15 or 16, wherein the hot isostatic pressing operates at a pressure of 60 MPa to 175 MPa.

[0072] Embodiment 18 is a method of any one of embodiments 1 -17, wherein the load transmitting powder is a ceramic powder.

[0073] Embodiment 19 is a method of any one of embodiments 1 -18, wherein the Load transmitting powder comprises alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof.

[0074] Embodiment 20 is a method of any one of embodiments 1 -19, wherein the densified article has an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0075] Embodiment 21 is a method for densifying comprising depositing metal powder to form a green body using an additive manufacturing process; sinteringthe green body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surrounding the dense body in a load transmitting powderwithin an enclosure; and subjecting the dense body and the load transmitting powder to isostatic pressingto provide a densified article.

[0076] Embodiment 22 is a method of embodiment 21 , wherein the green body has at least one open cavity.

[0077] Embodiment 23 is a method of any one of embodiments 21 or 22, wherein the at least one open cavity comprises at least 5% of the volume of the green body.

[0078] Embodiment 24 is a method of any one of embodiments 21 -23, wherein the additive manufacturing process is a binder jet process.

[0079] Embodiment 25 is a method of any one of embodiments 21 -24, wherein the metal powder comprises beryllium.

[0080] Embodiment 26 is a method of any one of embodiments 21 -25, wherein the metal powder comprises at least 95% by weight of beryllium based on the total weight of the metal powder.

[0081] Embodiment 27 is a method of any one of embodiments 21 -26, wherein the metal powder comprises less than 1% by weight of cobalt based on the total weight of the metal powder.

[0082] Embodiment 28 is a method of any one of embodiments 21 -27, wherein the metal powder comprises less than 1% by weight of nickel based on the total weight of the metal powder.

[0083] Embodiment 29 is a method of any one of embodiments 21 -28, wherein at Least 50% of the metal powder have an aspect ratio of 2:1 to 1 :1 .

[0084] Embodiment 30 is a method of any one of embodiments 21 -29, wherein the metal powder has an irregular morphology.

[0085] Embodiment 31 is a method of any one of embodiments 21 -30, wherein the metal powder has an average diameter of less than or equal to 45 microns.

[0086] Embodiment 32 is a method of any one of embodiments 21 -31 , wherein the metal powder has a bimodal distribution.

[0087] Embodiment 33 is a method of any one of embodiments 21 -32, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder from 10:1 to 2:1 , preferably from 8:1 to 4:1 , wherein the coarse metal has an average diameter from 50 to 400 microns, and the fine metal powder has an average diameter from 25 to 40 microns.

[0088] Embodiment 34 is a method of any one of embodiments 21 -33, wherein the isostatic pressing comprises cold isostatic pressing or hot isostatic pressing.

[0089] Embodiment 35 is a method of embodiment 34, wherein the hot isostatic pressing operates at a temperature up to 1150°C.

[0090] Embodiment 36 is a method of any one of embodiments 34 or 35, wherein the hot isostatic pressing operates at a pressure of 60 MPa to 175 MPa.

[0091] Embodiment 37 is a method of any one of embodiments 21 -36, wherein the load transmitting powder is a ceramic powder.

[0092] Embodiment 38 is a method of any one of embodiments 21 -37, wherein the load transmitting powder comprises alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof.

[0093] Embodiment 39 is a method of any one of embodiments 21 -38, wherein the densified article has an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0094] Embodiment 40 is a method for densifying comprising depositing metal powder to form a fused article using an additive manufacturing process; sintering the fused article at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphereto form a dense body; surrounding the dense body in a load transmitting powder within an enclosure; and subjecting the dense body and the load transmitting powder to isostatic pressingto provide a densified article.

[0095] Embodiment 41 is the method of embodiment 40, wherein the fused article has at least one open cavity.

[0096] Embodiment 42 is the method of any one of embodiments 40 or 41 , wherein the at least one open cavity comprises at least 5% of the volume of the first body.

[0097] Embodiment 43 is the method of any one of embodiments 40-42, wherein the additive manufacturing process is a laser powder bed fusion process.

[0098] Embodiment 44 is the method of any one of embodiments 40-43, wherein the metal powder comprises beryllium.

[0099] Embodiment 45 is the method of any one of embodiments 40-44, wherein the metal powder comprises at least 95% by weight of beryllium based on the total weight of the metal powder.

[0100] Embodiment 46 is the method of any one of embodiments 40-45, wherein the metal powder comprises less than 1% by weight of cobalt based on the total weight of the metal powder.

[0101] Embodiment 47 is the method of any one of embodiments 40-46, wherein the metal powder comprises less than 1% by weight of nickel based on the total weight of the metal powder.

[0102] Embodiment 48 is the method of any one of embodiments 40-47, wherein at least 50% of the metal powder have an aspect ratio of 2:1 to 1 :1 .

[0103] Embodiment 49 is the method of any one of embodiments 40-48, wherein the metal powder has an irregular morphology.

[0104] Embodiment 50 is the method of any one of embodiments 40-49, wherein the metal powder has an average diameter of less than or equal to 45 microns.

[0105] Embodiment 51 is the method of any one of embodiments 40-50, wherein the metal powder has a bimodal distribution.

[0106] Embodiment 52 is the method of any one of embodiments 40-51 , wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder from 10:1 to 2:1 , preferably from 8:1 to 4:1 , wherein the coarse metal has an average diameter from 50 to 400 microns, and the fine metal powder has an average diameter from 25 to 40 microns.

[0107] Embodiment 53 is the method of any one of embodiments 40-52, wherein the isostatic pressing comprises cold isostatic pressing or hot isostatic pressing.

[0108] Embodiment 54 is the method of embodiment 53, wherein the hot isostatic pressing operates at a temperature up to 1150°C.

[0109] Embodiment 55 is the method of any one of embodiments 53 or 54, wherein the hot isostatic pressing operates at a pressure of 60 MPa to 175 MPa.

[0110] Embodiment 56 is the method of any one of embodiments 40-55, wherein the load transmitting powder is a ceramic powder.

[0111] Embodiment 57 is the method of any one of embodiments 40-56, wherein the load transmitting powder comprises alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof.

[0112] Embodiment 58 is the method of any one of embodiments 40-57, wherein the densified article has an apparent density that is greater than 90% of the theoretical density, more preferably greater than 99.5%.

[0113] The present disclosure has been described with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understandingthe preceding detailed description. It is intended the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims orthe equivalents thereof. In some embodiments, any or some of the steps or components disclosed herein may be considered optional. In some cases, any or some of the aforementioned items in this description may be expressly excluded, e.g., via claim language. For example claim language may be modified to recite additional process steps.

[0114] The present disclosure is further understood by the following non-limiting examples.Examples

[0115] Beryllium powderwas used to from cylinders using an binder jet additive manufacturing process. The cylinders had a density of greater than 65%. Example 1 was sintered at 1220 °C and Example 2 was sintered at 1270 °C. After sintering the cylinders were loaded into an enclosure and surrounded by alumina followed by vacuum evacuation and sealing. The sealed cylinders were subject to a hot isostatic pressing (HIP) at 1000 °C and 103.4 Mpa (15 ksi). The cylinders were removed from the HIP enclosure and depowdered. Six samples were run for each examples, the averages are reported in Table 2. The 0.2% offset yield strength and ultimate tensile strength are measured according to ASTM E8. The % elongation is measured according to ASTM E3. The theoretical density of beryllium is 1 .85 g / cc.Table 2Theoretical 0.2% offset yield Ultimate TensileExample Density (%) strength (MPa) Strength (MPa) Elongation %1 100.36 215.9 286.1 2.262 100.30 218.3 289.8 2.05

[0116] Some of the samples for each example were tested to determine the weight percentage of carbon and oxygen. The weight percentage of BeO was calculated by multiplying the weight percentage of O by 1.5633. Based on these calculation the weight percentage of BeO was determined to be less than 1 .5 wt% which is below target levels of 2.0 wt%. The compositions are reported in Table 3.Table 3Example Sample C (wt%) O (wt%) BeO (wt%)1 1 0.464 0.456 0.7131 2 0.59 0.594 0.9291 3 0.507 0.515 0.8052 4 0.554 0.844 1.3192 5 - 0.693 1.083

[0117] While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. In view of the foregoing discussion, relevant knowledge in the art and references discussed above in connection with the Background and Detailed Description, the disclosures of which are all incorporated herein by reference. In addition, it should be understood that aspects of the invention and portions of various embodiments and various features recited below and / or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of skill in the art. Furthermore, those of ordinary skill in the art will appreciate the foregoing description is byway of example only, and is not intended to limit.

Claims

We Claim:1 . A method for densifying comprising: depositing metal powder to form a first body using an additive manufacturing process; sintering the first body at a temperature from 825°C to 1275°C in a reducing atmosphere or an inert atmosphere to form a dense body; surroundingthe dense body in a load transmitting powder within an enclosure; and subjecting the dense body and the load transmitting powder to isostatic pressing to provide a densified article.

2. The method of claim 1 , wherein the first body has at least one open cavity.

3. The method of claim 2, wherein the at least one open cavity comprises at least 5% of the volume of the first body.

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

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

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

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

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

10. The method of any one of claims 1 -9, wherein the bimodal distribution has a ratio of coarse metal powder to fine metal powder from 10:1 to 2:1 , preferably from 8:1 to 4:1 , wherein the coarse metal has an average diameter from 50 to 400 microns, and the fine metal powder has an average diameter from 25 to 40 microns.11 . The method of any one of claims 1 -10, wherein the isostatic pressing comprises cold isostatic pressing or hot isostatic pressing.

12. The method of any one of claims 1 -11 , wherein the load transmitting powder comprises alumina, silicon carbide, zirconia, titania, fused silica, or combinations thereof.

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

14. The method of any one of claims 1 -13, wherein the additive manufacturing process is a binder jet process, and wherein the first body is a green body.

15. The method of any one of claims 1 -13, wherein the additive manufacturing process is a laser powder bed fusion process, and wherein the first body is a fused article.