CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to United States Provisional Application No. 63/341,476, filed May 13, 2022, which is incorporated into this application by reference.

BACKGROUND

[0002] Due to their high density (17-18.5g/cm ³ ), high mechanical properties, and good machinability, tungsten heavy alloys (WHA) have many applications ranging from radiation shields to kinetic energy penetrators. These alloys are produced from powder blends containing W elemental powder (in the range 90-98 wt%) and additions of two or more of the elements consisting of Ni, Fe, Co, Cu. Typically a W powder with a size of approximately 4-5 pm is used.

[0003] W powder is produced industrially by reduction of WOs under a H2 atmosphere. The morphology of the W powder that results is highly irregular. Ni, Fe, Co and Cu powders are produced by melt atomization or other chemical processes. Since the W particles are small and of highly irregular shape, the WHA powder blends have very poor flow characteristics (“non-flowable powders”).

[0004] Recently, additive manufacturing (AM) has emerged as a potential production process for WHA products especially for net or near-net shape complex geometries which require extensive machining when produced from conventionally compacted blanks.

[0005] Additive manufacturing refers to several technologies that produce parts in an additive way. The starting point is a digital 3D model of a part which is then sliced in thin layers by computer software. An additive manufacturing machine builds the part from this series of layers - each one applied directly on top of the previous one.

[0006] Of the different AM technologies, the ones that are best suited for the production of WHA components are the ones based on powder bed systems. In these systems, a uniform layer of powder, typically 20-50 microns thick, is deposited on the building platform and consolidated. The powder platform descends by the layer thickness and a subsequent layer of powder is delivered and consolidated. The process is repeated until the complete part is formed.

[0007] Two approaches have been developed to consolidate 3D printed WHA powders: 1) Selective laser or electron beam melting/sintering (SLM and EBM) and 2) binder jet 3D printing (BJ3DP) followed by debinding and sintering.

[0008] In SLM each layer of powder is sintered/melted by a focused laser or electron beam, immediately after each powder layer is deposited (FIG. 2). In BJ3DP a printing head scans the surface of the powder depositing a binder on the area defined by a layer of the model (FIG. 3). In BJ3DP, when the printing is completed the part produced is in the green state (powder particles embedded in a binder matrix) and surrounded by lose powder. The lose powder is removed (de-powdering) to expose the part. When BJ3DP is applied to metals, the green part is subsequently consolidated by removing the binder thermally or chemically, and by sintering under a proper atmosphere.

[0009] Powder bed systems require powders with excellent flowability in order to deposit power layers with uniform density that, in turn, result in consistent shrinkage during the densification step. Typical powder size requirements are shown in Table 1.

Table 1. Powder Size for Different AM Technologies

[0010] To meet the flowability requirements, most metal powders currently used are spherical and produced by the gas atomization process. Given that gas atomization is not practical for producing W powder, the plasma spheroidization (or densification) process has been proposed to produce spherical WHA powder. There are, however, several shortcomings to this approach. The powder manufacturing process is very energy-intensive and, consequently, has a very large CO2 footprint. Secondly, although spherical powders (FIG. 4) with smooth surface have very good flow properties, they have very low green strength, which is problematic for the BJ3DP process. Lastly, the lengthy powder manufacturing process results in a very high powder cost. The cost of this powder can be 2 to 3 times higher than the cost of the original powder mix, greatly constraining the practical application of BJ3DP to WHA.

SUMMARY

[0011] The predominantly non-spherical composite tungsten heavy alloy powders can comprise tungsten particles bonded to or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum. In some embodiments, the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder. In some embodiments, the composite tungsten heavy alloy powder has the following characteristics: a median particle size (D50) ranging from 10-100 pm; and a D<>o of less than 100 pm. In some embodiments, the composite tungsten heavy alloy powder is produced from a tungsten heavy alloy scrap feedstock having an average sintered tungsten grain size of 35 pm or less.

[0012] The composite tungsten heavy alloy powders can be used in a variety of applications, including a powder bed-based additive manufacturing (AM) process using the composite tungsten heavy alloy powder.

[0013] The method of making a tungsten heavy alloy body can generally comprise providing a composite tungsten heavy alloy powder comprising tungsten particles bonded or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum; wherein the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder; and wherein the composite tungsten heavy alloy powder has the following characteristics: a median particle size (D50) ranging from 10-100 pm; and a D90 of less than 100 pm. A green body can be 3D printed from the provided composite tungsten heavy alloy powder, and the green body can be sintered to form the composite tungsten heavy alloy body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing summary, as well as the following description of the disclosure, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, the drawings illustrate some, but not all, alternative embodiments. This disclosure is not limited to the precise arrangements and instrumentalities shown. The following figures, which are incorporated into and constitute part of the specification, assist in explaining the principles of the disclosure.

[0015] FIG. 1 is an image showing the microstructure of sintered WHA. The sintered microstructure consists of relatively round body centered cubic (BCC) tungsten grains dispersed in a solidified face centered cubic (FCC) matrix phase.

[0016] FIG. 2 is a schematic of a typical SLM machine.

[0017] FIG. 3 is a schematic of a Binder Jetting 3D Printing (BJ3DP) machine.

[0018] FIG. 4A is an SEM micrograph showing spherical plasma densified WHA powder.

[0019] FIG. 4B is an SEM micrograph showing spherical plasma densified WHA powder.

[0020] FIG. 5A is an SEM micrograph showing the new, non-spherical, irregularly shaped Zn reclaimed WHA powder (NP).

[0021] FIG. 5B is an SEM micrograph showing the new, non-spherical, irregularly shaped Zn reclaimed WHA powder (NP).

[0022] FIG. 6A is an SEM micrograph showing the standard, non-spherical, irregularly shaped Zn reclaimed WHA powder.

[0023] FIG. 6B is an SEM micrograph showing the standard, non-spherical, irregularly shaped Zn reclaimed WHA powder.

[0024] FIG. 7 is an optical micrograph that shows the reaction of WHA with Zn. The heavy metal part is exposed to liquid Zn at 600°C for 3 h. At the reaction interface Ni-Fe-containing y-phase is formed [1] in contact with metallic binder [2], It grows into the binder area and shifts the W grains grain by grain towards the melt [3], Further access becomes possible. The reaction is governed by diffusion of Zn into the Fe-Ni-W binder.

[0025] FIG. 8 is a high level flow chart of the Zn reclaim process to produce WHA powder.

[0026] FIG. 9A is an SEM micrograph showing the morphology of the standard WHA powder. [0027] FIG. 9B is an SEM micrograph showing the morphology of the standard WHA powder.

[0028] FIG. 10 is a plot showing the proportion of the total volume of the particles in each sphericity range for the Plasma Densified Powder (PD) and for the New Powder (NP).

[0029] FIG. 11 is a plot showing the proportion of the total volume of the particles in each aspect ratio range for the Plasma Densified Powder (PD) and for the New Powder (NP).

[0030] FIG. 12A is an SEM micrograph showing backscattered electron (BEI) image in the spherical plasma densified WHA powder.

[0031] FIG. 12B is an SEM micrograph showing the Fe distribution in the spherical plasma densified WHA powder.

[0032] FIG. 12C is an SEM micrograph showing the Ni distribution in the spherical plasma densified WHA powder.

[0033] FIG. 12D is an SEM micrograph showing the W distribution in the spherical plasma densified WHA powder.

[0034] FIG. 13A is an SEM micrograph showing BEI image in the new WHA powder.

[0035] FIG. 13B is an SEM micrograph showing the Fe distribution in the new WHA powder.

[0036] FIG. 13C is an SEM micrograph showing the Ni distribution in the new WHA powder.

[0037] FIG. 13D is an SEM micrograph showing the W distribution in the new WHA powder.

[0038] FIG. 14A is a photograph showing a few of the sintered and printed rods.

[0039] FIG. 14B is a schematic showing the dimensions of the tensile sample.

[0040] FIG. 15 is a plot showing the variation in green strength of printed samples at different saturation levels for the Plasma Densified Powder (PD) and for the New Powder (NP). [0041] FIG. 16A is an image showing the pore-free microstructure of sintered BJ3DP samples for the new Zn reclaimed Powder.

[0042] FIG. 16B is an image showing the pore-free microstructure of sintered BJ3DP samples for the new Zn reclaimed powder.

[0043] FIG. 16C is an image showing the pore-free microstructure of sintered BJ3DP samples for the Plasma Densified Powder.

[0044] FIG. 16D is an image showing the pore-free microstructure of sintered BJ3DP samples for the Plasma Densified Powder.

[0045] FIG. 16E is an image showing the low density, pore containing microstructure of sintered BJ3DP samples for the standard Zn reclaimed powder.

[0046] FIG. 16F is an image showing the low density, pore containing microstructure of sintered BJ3DP samples for the standard Zn reclaimed powder.

[0047] FIG. 17A is a photograph showing a WHA casting mold insert (chills) produced by BJ3DP (dimensions 1.5 x 4 in)

[0048] FIG. 17B is a photograph showing a WHA casting mold insert (chills) produced by BJ3DP (dimensions 1.5 x 4 in)

[0049] FIG. 18A is a photograph showing examples of BJ3DP WHA parts with helical gear with integral dog clutch.

[0050] FIG. 18B is a photograph showing examples of BJ3DP WHA parts with spiral bevel gear.

[0051] FIG. 19 is a high level flow chart of the AM WHA powder manufacturing processes.

[0052] FIG. 20 is a flow chart showing the dissolution, purification and conversion of W ore concentrate to pure ammonium paratungstate (APT). The liquid ion exchange (LIX) process is common in Western countries, the solid ion exchange process (SIX) is widely used in China. [0053] FIG. 21 is a plot showing Calculated CO2 emissions for the WHA powder manufacturing processes. (Calculations per ISO 14064, Scope 1, Scope 2, Scope 3.)

DETAILED DESCRIPTION

A. Definitions

[0054] “D50” refers to the particle diameter of the powder where 50 weight % of the particles in the total distribution of the reference sample have the noted particle diameter or smaller.

[0055] Similarly, “D90” refers to the particle diameter where 90 weight % of the particles in the total distribution of the reference sample have the noted particle diameter or smaller. Particle sizes can be measured by any suitable method including laser diffraction. In this case, powder size distribution was measured using a Malvern, Mastersizer 2000 per the ASTM B822 standard.

[0056] An “an average sintered tungsten grain size” refers to the average size of tungsten grains in a sintered microstructure, as measured according to TEM image analysis software known in the art or as determined using the mean linear intercept grain size of the tungsten grains to express the mean tungsten grain size. The mean linear intercept is the intercept length averaged over all directions.

[0057] When the term “about” precedes a numerical value, the numerical value can vary within ±10% unless specified otherwise.

[0058] The terms “powder” and “particles” are meant to include particulate having a variety of shapes and sizes, including generally spherical or irregular shapes, flakes, needle-like particles, chips, fibers, equiaxed particles, etc.

B. Composite Tungsten Heavy Alloy Powders

[0059] The composite tungsten heavy alloy powders are generally used for additive manufacturing of parts, among other applications, due to characteristics of the composite powders (homogeneity and uniform bonding of W particles with alloying elements) that are required in such applications. In one embodiment, the predominantly non-spherical composite tungsten heavy alloy powder comprises tungsten particles bonded or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum.

[0060] In some embodiments, the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder. In further embodiments, the composite tungsten heavy alloy powder has the following characteristics: (a) a median particle size (D50) ranging from 10-100 pm; (b) a D90 of less than 100 pm.

[0061] In some embodiments, the composite tungsten heavy alloy powder has a high apparent density that is suitable for a variety of additive manufacturing techniques, by enabling a highly packed powder bed which is critical for improved sintering densification. The powder in some aspects also has suitable dispersability and flow characteristics that aid in such manufacturing techniques.

[0062] In one embodiment, the composite tungsten heavy allow powder has an apparent density of at least 6 g/cm ³ . In a further embodiment, the tungsten heavy alloy powder has an apparent density of at least 7 g/cm ³ . In a still further embodiment, the tungsten heavy alloy powder has an apparent density ranging from 7-10 g/cm ³ .

[0063] The particle size of the composite tungsten heavy alloy powder can also provide for improved ability to use the powder in additive manufacturing techniques. In one embodiment, the composite tungsten heavy alloy powder has a D50 ranging from 15-30 pm. In a further embodiment, the composite tungsten heavy alloy powder has a D90 of less than 50 pm. In further embodiments, the composite tungsten heavy alloy powder has an average particle size of 35 pm or less. In still further embodiments, the composite tungsten heavy alloy powder has an average particle size of 25 pm or less.

[0064] The disclosed composite tungsten heavy alloy powders also exhibit good flowability. In some embodiments, the composite tungsten heavy alloy powder exhibits a flowability ranging from 8 seconds per 50 grams to 15 seconds per 50 grams, as measured by a Hall flowmeter. In further embodiments, the composite tungsten heavy' alloy powder exhibits a flowability of about 10 seconds per 50 grams, as measured by a Hall flowmeter.

[0065] The disclosed particle shape of the composite tungsten heavy alloy powder is also desirable for a variety of applications. The predominantly irregular shape can make the as printed part strong and easy to handle by increasing the interlocking of the particles within the powder. In some embodiments, less than 20% by volume of the powder has a sphericity in the range of 0.95-1. In further embodiments, less than 17% by volume of the powder has a sphericity in the range of 0.95-1. Similarly, in other embodiments, less than 25% by volume of the powder has an aspect ratio of 0.85 or greater. In further embodiments, less than 15% by volume of the powder has an aspect ratio of 0.9 or greater. In still further embodiments, less than 5% by volume of the powder has an aspect ratio of 0.95 or greater.

[0066] As described above in terms of composition of the composite powders, in some embodiments, the composite powder comprises tungsten particles bonded or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum. The bonding and coating morphology of the powder can be readily determined my microscopy techniques, such as SEM. In further embodiments, the composite tungsten heavy alloy powder comprises tungsten; and two or more of nickel, iron, cobalt, and copper in the matrix binder. In other embodiments, the composite tungsten heavy alloy powder comprises tungsten; and nickel and iron in the matrix binder.

[0067] The weight percentages of tungsten and other metals in the matrix binder (by weight the composite powder) can vary. In one embodiment, the composite tungsten heavy alloy powder comprises tungsten in an amount ranging from 90-97% by weight of composite tungsten heavy alloy powder. In a further embodiment, the composite tungsten heavy alloy powder comprises nickel in the matrix binder in an amount ranging from 4-7% by weight of composite tungsten heavy alloy powder. In a still further embodiment, the composite tungsten heavy alloy powder comprises iron in the matrix binder in an amount ranging from 1-3% by weight of composite tungsten heavy alloy powder.

[0068] In one specific embodiment, the composite tungsten heavy alloy powder comprises tungsten in an amount ranging from 90-97% by weight of composite tungsten heavy alloy powder, nickel in the matrix binder in an amount ranging from 4-7% by weight of composite tungsten heavy alloy powder, and iron in the matrix binder in an amount ranging from 1-3% by weight of composite tungsten heavy alloy powder. C. Methods of Making the Composite Tungsten Heavy Alloy Powders

[0069] In general, the composite tungsten heavy allow powders can be made using a zinc reclaim process with tungsten heavy allow solid scrap as a feedstock. The process is shown in the flow chart of FIG. 8. In the first step, cleaned and sorted tungsten heavy alloy scrap can be contacted with molten Zn at 600- l()5() C under an inert atmosphere (e.g., N2 atmosphere) for a suitable time, typically several hours. In some embodiments, the tungsten heavy alloy scrap has an average particle size of 35 microns or less, e.g., 25 microns or less. The second step involves the distillation ofZn under vacuum (0.06-0.13 mbar) at 1000-1050°C for a suitable time, typically several hours. The cooled down material can then be crushed, ball milled, and screened. Optionally, the top screen (material that did not react fully with Zn) can be recycled into the next batch. The crushing and milling involve fracture, primarily of the binder matrix phase and not the tungsten phase.

[0070] The disclosure also relates to a powder bed-based additive manufacturing (AM) process using any of the described composite tungsten heavy alloy powders.

D. Methods of Making Composite Tungsten Heavy Alloy Bodies

[0071] Also described is a method of making a tungsten heavy alloy body. In some embodiments, the method comprises providing a composite tungsten heavy alloy powder comprising tungsten particles bonded to or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum (including any of the specific composite tungsten heavy' alloy powders described above). In some embodiments, the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder. In other embodiments, the composite tungsten heavy alloy powder has the following characteristics: (a) a median particle size (D50) ranging from 10-100 pm; and (b) a Ds>o of less than 100 pm.

[0072] The method further comprises 3D printing a green body from the composite tungsten heavy' alloy powder and a printing binder, followed by sintering the green body to form the composite tungsten heavy alloy body. In some embodiments, the method further comprises sinter-HIPing the green body or the tungsten heavy alloy body. In further embodiments, the step of 3D printing the tungsten heavy alloy body from the powder consolidating the powder using energy from a laser or an electron beam to thereby form the tungsten heavy alloy body. In further embodiments, the method further comprises the step of sinter-HIPing the tungsten heavy body after the 3D printing step.

[0073] In some embodiments, the 3D printing step comprises selective laser melting (SLM), electron beam melting (EBM), or direct energy deposition (DED).

[0074] A variety of tungsten heavy alloy bodies can be prepared according to the disclosed method. In some embodiments, the tungsten heavy alloy body is a balancing weight for a rotorcraft application, a balancing weight for an internal combustion engine crankshaft, a radiation shielding component, a chill for a die-casting mold, or a penetrator or an array thereof for a kinetic energy device.

E. Exemplary Embodiments

[0075] A predominantly non-spherical composite tungsten heavy alloy powder comprising tungsten particles bonded or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum; wherein the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder; wherein the composite tungsten heavy alloy powder has the following characteristics: a median particle size (D50) ranging from 10-100 pm; a D90 of less than 100 pm; and wherein the composite tungsten heavy alloy powder is produced from a tungsten heavy alloy scrap feedstock having an average sintered tungsten grain size of 35 pm or less.

[0076] The preceding composite, wherein the composite tungsten heavy alloy powder is produced from a tungsten heavy alloy scrap feedstock having an average sintered tungsten grain size of 25 pm or less.

[0077] Any preceding composite, which is prepared by recycling the tungsten heavy alloy scrap feedstock using a zinc reclaim process.

[0078] Any preceding composite, wherein the zinc reclaim process comprises contacting the tungsten heavy alloy scrap feedstock with molten zinc followed by vacuum distilling at least a portion of the zinc.

[0079] Any preceding composite, having an apparent density of at least 6 g/cm ³ . [0080] Any preceding composite, having an apparent density of at least 7 g/cm ³ .

[0081] Any preceding composite, having an apparent density ranging from 7-10 g/cm ³ .

[0082] Any preceding composite, having a Dso ranging from 15-30 pm.

[0083] Any preceding composite, having a D90 of less than 50 pm.

[0084] Any preceding composite, which exhibits a flowability ranging from 8 seconds per 50 grams to 15 seconds per 50 grams, as measured by a Hall flowmeter.

[0085] Any preceding composite, which exhibits a flowability of about 10 seconds per 50 grams, as measured by a Hall flowmeter.

[0086] Any preceding composite, wherein less than 20% by volume of the powder has a sphericity in the range of 0.95-1.

[0087] Any preceding composite, wherein less than 17% by volume of the powder has a sphericity in the range of 0.95-1.

[0088] Any preceding composite, wherein less than 25% by volume of the powder has an aspect ratio of 0.85 or greater.

[0089] Any preceding composite, wherein less than 15% by volume of the powder has an aspect ratio of 0.9 or greater.

[0090] Any preceding composite, wherein less than 5% by volume of the powder has an aspect ratio of 0.95 or greater.

[0091] Any preceding composite, comprising tungsten and two or more of nickel, iron, cobalt, and copper in the matrix binder.

[0092] Any preceding composite, comprising tungsten; and nickel and iron in the matrix binder.

[0093] Any preceding composite, comprising tungsten in an amount ranging from 90-97% by weight of composite tungsten heavy alloy powder. [0094] Any preceding composite, comprising nickel in the matrix binder in an amount ranging from 4-7% by weight of composite tungsten heavy alloy powder.

[0095] Any preceding composite, comprising iron in the matrix binder in an amount ranging from 1-3% by weight of composite tungsten heavy alloy powder.

[0096] Any preceding composite, comprising tungsten in an amount ranging from 90-97% by weight of composite tungsten heavy alloy powder, nickel in the matrix binder in an amount ranging from 4-7% by weight of composite tungsten heavy alloy powder, and iron in the matrix binder in an amount ranging from 1-3% by weight of composite tungsten heavy alloy powder.

[0097] A powder bed-based additive manufacturing (AM) process using the composite tungsten heavy alloy powder of any preceding embodiment.

[0098] A method of making a tungsten heavy alloy body, the method comprising: a) providing a composite tungsten heavy alloy powder comprising tungsten particles bonded or partially coated with a matrix binder comprising at least two elements selected from nickel, iron, cobalt, copper, and molybdenum; wherein the composite tungsten heavy alloy powder comprises 90% by weight or more of tungsten and 10% by weight or less of the matrix binder; and wherein the composite tungsten heavy alloy powder has the following characteristics: i) a median particle size (D50) ranging from 10-100 pm; and ii) a D90 of less than 100 pm; b) 3D printing a green body from the composite tungsten heavy alloy powder and a printing binder; and c) sintering the green body to form the composite tungsten heavy alloy body.

[0099] The preceding method, wherein the composite tungsten heavy alloy powder is produced from a tungsten heavy alloy scrap feedstock having an average sintered tungsten grain size of 35 pm or less.

[00100] Any preceding method, wherein the composite tungsten heavy alloy powder is produced from a tungsten heavy alloy scrap feedstock having an average sintered tungsten gram size of 25 pm or less.

[00101] Any preceding method, further comprising sinter-HIPing the green body or the tungsten heavy alloy body. [00102] A method of making a tungsten heavy alloy body, the method comprising 3D printing the tungsten heavy alloy body from the powder of any preceding embodiment by consolidating the powder using energy from a laser or an electron beam to thereby form the tungsten heavy alloy body.

[00103] The preceding method, further comprising the step of sinter-HIPing the tungsten heavy body after the 3D printing step.

[00104] Any one of the preceding two methods, wherein the 3D pnnting step comprises selective laser melting (SLM), electron beam melting (EBM), or direct energy deposition (DED).

[00105] Any one of the preceding three methods, wherein tungsten heavy alloy body is a balancing weight for a rotorcraft application, a balancing weight for an internal combustion engine crankshaft, a radiation shielding component, a chill for a die-casting mold, or a penetrator or an array thereof for a kinetic energy device.

F. Examples

[00106] The following examples further illustrate this disclosure. The scope of the disclosure and claims is not limited by the scope of the following examples.

1. WHA Powder Manufacturing Process

[00107] According to one embodiment, a WHA scrap is treated by molten Zn to produce a WHA powder with only a very gentle post zincing grinding step. An intensive grinding would deform, break or otherwise change the morphology and the physical characteristics of recycled WHA powder. To achieve specific characteristics for the as recycled WHA powder, the feed WHA scrap is preferably produced using standard manufacturing processes for WHA components. However, the as produced component microstructure preferably has an average W grain size of 35 microns or smaller and in some embodiments, 25 microns or smaller. It will be understandable that such a small W grain in the component sintered microstructure can be achieved by a controlled sintering cycle where temperature and time at temperature are optimized. [00108] A WHA scrap meeting the above characteristics for W grain size is treated in molten Zn, which reacts with the low temperature melting binder matrix and separates it from W particles. The optical micrograph in FIG 7 shows the reaction mechanisms and the separation of the different phases of WHA metal exposed to liquid Zn at 600°C for 3h.

[00109] The reaction is governed by diffusion of Zn into the Fe, Ni and/or Co-rich binder. The separation of the different phases is governed by the reaction of liquid Zn with the (Ni, Fe, Co) rich binder matrix and the formation of Zn-rich intermetallic phases (yl, 5, y). The formation of these intermetallic phases at the reaction front is followed by crack formation along the reaction interface and by further penetration of the Zn-melt in the reacting body. These reactions lead to a volume expansion of the matrix alloy and bloat the scrap. After vacuum distillation of the Zn, the material is friable and can be readily disintegrated. The condensed Zn can be re-used. The reclaimed WHA sponge contains < 50 ppm Zn.

[00110] FIG. 8 shows a high-level flow chart for the process. In the first stage, the cleaned and sorted WHA scrap is contacted with molten Zn at 600-1050°C under aN2 atmosphere for several hours. The second stage is the distillation of Zn under vacuum (0.06- 0.13 mbar) at 1000-1050°C, which can take several hours. The cooled down material is crushed, ball milled and screened. The top screen (material that did not react fully with Zn) can be recycled into the next batch. The crushing and milling involve fracture, primarily of the matrix phase and not the W phase. A detailed characterization of the WHA powder is provided in the following discussion.

[00111] While recovery of tungsten from heavy metal alloys by Zn treatment was described by Vanderpool et al. (US 4,338,126), the recycled powder requires grinding in order to be used for part manufacturing. As described in the ’ 126 patent, “the reclaimed powder mixture is readily ground to a powder of particle size similar to the original material and may be further reused in the preparation of heavy metal alloys.” Using a standard WHA scrap, it would be expected that Vanderpool recycled powder will not meet the particle dimensional characteristics for additive manufacturing applications. Such powder will also fail to sinter to full density and therefore cannot be used as such for manufacturing WHA components with ideal mechanical properties. [00112] The following table further illustrates differences in powder characteristics between the process claimed by Vanderpool et al. in the ’ 126 patent and the powders prepared according to the disclosed process.

2. WHA Powder Characterization a. Experimental Procedure

[00113] Four different WHA powders with similar chemical composition were produced and tested. Three of the powders were tested for powder-bed-based additive manufacturing, and a reference powder (standard premix powder) produced by mixing the elemental powders in a V-blender was used for comparison. The standard premix was isostatically pressed for manufacturing the test rods. The other three powders were used in a binder jet printer for manufacturing the test rods. The chemical composition and the properties of these powders are summarized in Table 2.

Table 2. Chemical Composition and Physical Properties of Test Powders

[00114] The powder size distribution was measured using a Malvern, Mastersizer 2000 per the ASTM B822 standard. The particle shape characterization was carried out using a Camsizer XT per ISO 13322-2 with direct comparison between the plasma densified powder and the new powder.

[00115] A Hitachi S-3000N Scanning Electron Microscope (SEM) was used to generate images of the three powders. Backscattered electron images (BEI) showing the chemical contrast and X-ray maps of alloying elements were obtained from the two powders developed for additive manufactunng. b. Powder Morphology

[00116] The morphology of the standard WHA powder is shown in FIG 9A and FIG 9B. The W particles (4-6 pm) are bonded together forming large agglomerates. Such agglomerated powder results in compacts with non-uniform particle packing. In the standard manufacturing of WHA parts, the external compaction force helps particle rearrangement and promotes homogeneous distribution inside the molding tool. For additive manufacturing, a pre-processing of the fine W particles and the alloying elements into spherical granules is the best method to improve powder flow and powder packing to achieve a uniform distribution within the green component. Plasma densification is one known methods for creating homogeneous, spherical granules containing W and the alloying elements.

[00117] The particles of the plasma densified powder are shown in FIG 4A and FIG 4B. The plasma densified powder has spherical particles with smooth surface. Compared to the plasma densified powder, the Zn reclaimed powder micrographs in FIG 5 and FIG 6 show a more irregular shape and rough surface. However, the powder in FIG 5 has a smaller particle size than the powder in FIG 6. As explained above, the production of the powder in FIG. 5 uses a feed material with an average W grain size below 35 microns and in some embodiments 25 microns. [00118] Comparing the morphology of the Zn reclaimed powders to the morphology of the plasma densified powder, the plots in FIG. 10 and FIG 11 show the proportion of the total volume of particles in both powders whose shape is spherical (SPHT =1 and Aspect Ratio =1) and the classification of these two powders based on sphericity and aspect ratio ranges. The plasma densified powder has more particles in the sphericity range > 0.95 and more particles with aspect ratio > 0.85. c. Powder Flow

[00119] The Hall flow of the four powders is reported in Table 2. As expected, the premix powder does not flow while the plasma densified powder and the Zn reclaimed powders have a Hall flow of 10 seconds or less. In spite of the lower sphericity, the Zn reclaimed powders still exhibit excellent flow. d. Distribution of the Alloying Elements

[00120] A homogeneous distribution of alloying elements in the powder mix is critical for controlling sintering dimensions as well as sintered microstructures and sintered properties.

[00121] BEI images in FIG. 12A-FIG. 12D and FIG. 13A-FIG. 13D compare the distribution of the alloying elements between plasma densified powder and the new Zn reclaimed powder. Both powders show a very homogeneous distribution of Ni, Fe and W in the powder. However, the Zn reclaimed powder shows a presence of uniformly distributed binder rich particles with less W content.

3. Manufacturing of WHA Components Using the Binder Jetting 3D Printing a. Experimental Procedures

[00122] A comparison of green strength was made between the new Zn reclaimed powder and the plasma densified powder. Five samples per powder were tested for green strength (Table 3). The green strength measurements were earned out per the ASTM B312 standard using Tinius Olsen (H5KS) universal testing machine. Table 3. Green Strength Test Plan (ASTM B312)

[00123] Cylindrical rods (figure 14) were used for the assessment of sintered properties for all the four powders (standard premix powder, Zn reclaimed powders and plasma densified powder).. These rods were machined into tensile specimens after sintering. Rods from the standard powder mix were pressed isostatically at 241 MPa in a 25.4 mm diameter dry bag mold. After pressing, rods had approximately 16 mm diameter. Dry bag pressed rods from standard powder did not contain lubricant.

[00124] The new Zn reclaimed powders (NP and SZR) and the plasma densified (PD) powder were printed using an ExOne Innovent binder jetting 3D printer. A water based solvent binder was used for printing the samples. These samples were printed at 40%/65%/75% binder saturation and a powder layer thickness of 60 pm was used for printing. 18.54 mm diameter x 117.35 mm long specimens were printed at binder set time of 7sec and speed of 100 mm/sec. BJ3DP samples were cured for 6 hours by heating to 180°C before normal de-binding and sintering processes.

[00125] Binder Jet printed rods (Zn reclaimed and plasma densified powders) were debound at 750°C under a protective atmosphere prior to sintering. After de-binding, all the materials were sintered in a box furnace under flowing hydrogen to a maximum temperature of 1540°C, with a hold of Ih at max temperature. At this temperature, the plasma densified powder did not sinter to full density. A second sintering at 1550°C did not achieve full density either. After two trials, the temperature was increased to 1560°C to achieve full density. After sintering, all the rods were measured for density per the ASTM E8 standard. As sintered samples were mounted and polished for optical microscopy. [00126] Sintered rods were machined into tensile specimens (FIG 14A and FIG 14B) Tensile testing was conducted according to the ASTM E8 standard using a variable strain rate (0.015/min before yield and 0.15/min after yield). b. Green Strength of the Printed Parts

[00127] As explained earlier, irregular particles are more likely to create stronger interlocking contacts as opposed to spherical particles. To assess the particle interlocking effect, the transverse rupture strength (TRS) was measured for the as-prmted-and-cured samples from the two AM powders. The strength as a function of saturation level is reported in FIG. 15. The strength increases with the increase in binder saturation with a maximum at 75% binder saturation. The parts printed using the new powder are 4x stronger than parts printed using plasma densified powder. Under similar printing conditions, clearly higher number of interlocking contacts between irregular particles as well as the higher roughness particle surface contributed to the difference in strength. c. Sintered Microstructure

[00128] The sintered microstructures are shown in FIG. 16A-FIG. 16F. The WHAs produced via BJ3DP using the new Zn reclaimed powder and the plasma densified powder are free of porosity and have microstructures that are very similar to those of WHA produced by conventional powder metallurgy (PM). The sintered microstructure of WHA component produced via BJ3DP using the standard Zn reclaimed powder shows porosity. d. Sintered Mechanical Properties

[00129] Binder jetting printed rods were sintered and tested for mechanical properties. Table 4 gives the density measured for each rod after sintering and the tensile properties from machined samples. Table 4. Sintered Density and Tensile properties of Binder Jet Printed Parts

Reclaimed Powder • SP=Standard Premix Powder • DB = Dry Bag Pressed • PD = Plasma Densified Powder

[00130] Density and tensile properties reported in Table 4 show that the sintered properties of the new Zn reclaimed powder manufactured using binder jetting technology' matches the properties of dry' bag pressed parts using standard WHA mix.

[00131] The standard Zn reclaimed powder does not sinter to full density due to large W particle size (FIG6A-FIG 6B). It is known that WHA sintering densification especially in the solid state sintering stage is partially controlled by W gram size. With large grams, the contribution of the grain boundary diffusion is reduced. [00132] Based on the sintered density and sintered microstructure, one could predict that mechanical properties of the standard Zn reclaimed powder will be lower. As shown in the Table 4, parts made with this powder do not meet minimum properties per the SAE AMS 7725F specification for the Class 2 WHA.

[00133] The presence of pores in the microstructure (FIG. 16 E- FIG 16F) and consequently, the low density of sintered parts made with standard Zn reclaimed powder prevent the utilization of this powder for manufacturing WHA components via AM techniques.

[00134] The plasma densified powder required higher temperature sintering to achieve equivalent properties in part because of the slightly higher W content but mostly due to slower sintering.

[00135] With one sintering cycle in the same furnace, the standard premix powder and the new Zn reclaimed powder achieved mechanical properties far superior to the specified minimum properties per the SAE AMS 7725F specification for the Class 2 WHA. The higher mechanical properties are in line with pore free microstructures after sintering as shown in FIG. 16A-FIG. 16B.

[00136] Finally, FIG. 17A-FIG 17B and FIG. 18A-FIG 18B provide examples of WHA parts produced with the new Zn reclaimed WHA powder using the BJ3DP process. WHA parts of great complexity can be produced to net or near-net shape using this technology.

4. Carbon Footprint and Cost

[00137] The process to produce W powder, the main constituent of WHA powders, is a very lengthy one involving many energy-intensive steps. Consequently, high levels of CO2 emissions are associated with its production.

[00138] Today WHA powder can be produced starting from W ore, or through recycling of W scrap. The two most widely used recycling processes are chemical recycling and the zinc process. [00139] FIG. 19 provides a high-level flow chart of WHA powder manufacturing processes, and FIG. 20 provides more details of the chemical purification and conversion to ammonium paratungstate (APT).

[00140] The chemical recycling process eliminates the need for the mining and ore beneficiations steps while adding an oxidation step. Overall, this results in an important reduction in CO2 emissions. The Zn reclaim goes even further by eliminating the need for chemical purification and conversion to APT, and the downstream steps to produce W oxide and W powder (FIG. 19). The Zn reclaim process adds the zincing step.

[00141] The plot in FIG. 21 summarizes the calculation of the CO2 emissions associated with the WHA powder manufacturing processes. The calculations follow the ISO methodology (ISO 14064, Scope 1 , Scope 2, Scope 3.)

[00142] The production of WHA powder results in a 95% and 86% reduction of CO2 emissions as compared to the production of WHA powder from W ore and through the chemical recycling process, respectively.

[00143] Finally, the greatly simplified Zn reclaim process also results in a reduction in the manufacturing cost of the WHA powder of approximately 50-66%, as compared to plasma densified WHA powder.

[00144] Features and advantages of this disclosure are apparent from the detailed specification, and the claims cover all such features and advantages. Numerous variations will occur to those skilled in the art, and any variations equivalent to those described in this disclosure fall within the scope of this disclosure. Those skilled in the art will appreciate that the conception upon which this disclosure is based may be used as a basis for designing other methods and systems for carrying out the several purposes of this disclosure. As a result, the claims should not be considered as limited by the description or examples.