具体实施方式：
[0026]These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims.
DETAILED DESCRIPTION
[0027]While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.
Definitions
[0028]In describing and claiming the present invention, the following terminology will be used.
[0029]The singular forms “a,”“an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a metal” includes reference to one or more of such materials and reference to “heating” refers to one or more of such steps.
[0030]As used herein with respect to an identified property or circumstance, “substantially” refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.
[0031]As used herein, the term “about” is used to provide flexibility and imprecision associated with a given term, metric or value. The degree of flexibility for a particular variable can be readily determined by one skilled in the art. However, unless otherwise enunciated, the term “about” generally connotes flexibility of less than 2%, and most often less than 1%, and in some cases less than 0.01%.
[0032]As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.
[0033]As used herein, the term “at least one of” is intended to be synonymous with “one or more of.” For example, “at least one of A, B and C” and “at least one of A, B, or C” explicitly includes only A, only B, only C, or combinations of each.
[0034]Numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly recited limits of 1 to about 4.5, but also to include individual numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than about 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.
[0035]Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein.
Example Embodiments
[0036]A gold-titanium alloy can be produced by the formation of parts from metal powders, either by a powder metallurgy (PM) or additive manufacturing (AM) approach, to make a well-segregated chemistry, refined grains, and a near-net-shape part with far less waste. FIG. 1 is a flowchart illustrating one example method 100 of making a gold-titanium alloy. This method includes preparing a powder mixture comprising a gold source powder and a titanium source 110; consolidating the powder mixture to form a consolidated body 120; and at least partially sintering the consolidated body in vacuum or a reducing atmosphere to form a gold-titanium alloy sintered article 130.
[0037]Another example method 200 of making a gold-titanium alloy is illustrated in FIG. 2. In this example, the method includes: preparing a composite metal powder having composite granules including a gold source powder and a titanium source powder within the composite granules 210; consolidating the composite metal powder to form a consolidated body 220; at least partially sintering the consolidated body to form a sintered article 230; and deoxygenating at least one of the composite metal powder, the consolidated body, or the sintered article at a deoxygenation temperature under a hydrogen-containing atmosphere to reduce an oxygen content 240.
[0038]Both of the example methods described above utilize a gold source powder and a titanium source powder to form a gold-titanium alloy. In some examples, the gold source powder and the titanium source powder can be blended together before forming a consolidated body and sintering the consolidated body. In certain examples, the blending can simply be dry blending a gold powder with a titanium powder. In this example, the powder mixture mentioned above can simply be an elemental blend of elemental gold powder mixed with elemental titanium powder. A consolidated body can be formed from this dry blend of elemental powders using any suitable method for forming a consolidated body, and the consolidated body can be sintered.
[0039]FIG. 3A shows an example of an elemental blend of gold powder 310 with titanium powder 320. These powders can have a variety of particle size distributions and morphologies, which are described in more detail below. The blend of powders can be consolidated to form a consolidated body 330, as shown in FIG. 3B. The consolidated body can be sintered to form a sintered article 340, as shown in FIG. 3C. This sintered article can be made of a gold-titanium alloy.
[0040]Another example method of making a gold-titanium alloy is illustrated in a flowchart in FIG. 4. A gold source powder 410 and a titanium source powder 420 are blended together to prepare blended elemental powders 412 as in the previous example. Optionally, additional element powders 422 can also be blended in, such as additional alloying metals. The blended elemental powders can be consolidated to form a consolidated green part 430. The consolidated green part can then be sintered to form a sintered article 440. This example also includes deoxygenation 450, which can be applied to the blended elemental powders, the consolidated green part, the sintered article, or any combination thereof. Titanium metal can be highly reactive with oxygen. Oxygen can also be dissolved in titanium metal. Therefore, it can be useful to perform a deoxygenation operation to reduce titanium oxide and also to remove dissolved oxygen from the titanium metal. In some examples, it can also be useful to apply a deoxygenation operation to the titanium source powder.
[0041]In further examples, the powder mixture can include composite granules made up of gold source powder and titanium source powder. The composite granules can be prepared by combining a gold source powder and a titanium source powder using a suitable granulation process to form granules, where each granule includes multiple gold powder particles and multiple titanium powder particles. The gold source powder and titanium source powder can be combined in a desired ratio and the granules can have approximately the same desired ratio of gold to titanium in each granule.
[0042]FIGS. 5A-5E show an example of a method of making a sintered article 540 using composite granules 525. FIG. 5A shows a dry blend of gold source powder 510 and titanium source powder 520. FIG. 5B shows a composite granule that can be formed using a suitable granulation method from the dry powder blend. In some examples, the granules can be sintered or partially sintered as individual granules to form sintered granules 535, as shown in FIG. 5C. However, in other examples the granules can be used without this sintering of the individual granules. FIG. 5D shows an example of preparing a consolidated body 530 from sintered granules. A final sintering operation is then performed to sinter the granules together, forming the final sintered article as shown in FIG. 5E.
[0043]In some examples, the composite granules can be useful because granulation can provide a low-energy method of making spherical or spheroidal particles from angular or irregular source powders. Spherical granules can be particularly useful in additive manufacturing methods that benefit from consistent size and shape and flowability of the particles. The granules can also be useful to increase compositional uniformity throughout the sintered article, because the gold and titanium can be evenly distributed at a uniform ratio in the granules. In some cases, when a dry blend of gold powder and titanium powder is prepared, some separation of the gold and titanium can occur due to the difference in density between gold and titanium. This can cause non-uniformity in the ratio gold and titanium is different locations in the final sintered article. Some additive manufacturing processes can be particularly susceptible to such separation of gold and titanium powder since the powders may separate in a feed hopper and/or in a powder bed, causing the ratio of gold to titanium to be different at different locations within the sintered article. Therefore, it can be useful to form granules that have an approximately uniform density and an approximately uniform composition so that this separation can be avoided. Granulation processes that can be used are described in more detail below.
[0044]Another example method is illustrated in a flowchart in FIG. 6. In this example, gold source powder 610 is combined with titanium source powder 620 and optionally additional source powders 622 in a granulation process 623. This forms a composite powder 625 that includes granules containing a mixture of the source powders. The composite powder is consolidated to form a consolidated green part 630. The consolidated green part is sintered to form a sintered article 640. A deoxygenation operation can be applied to the composite powder, the consolidated green part, the sintered article, or a combination thereof.
[0045]In some examples, the methods described herein can include an additive manufacturing process. Some additive manufacturing processes can additively build a green part that is subsequently sintered in a sintering furnace to form the final sintered part. Other additive manufacturing methods can form a final sintered part directly from the source powder material or from a composite powder. FIG. 7 shows a flowchart of another example method that involves additive manufacturing. In this example, gold source powder 710 is combined with titanium source powder 720 and optionally additional source powder 722 in a granulation process 723. This process forms a composite powder 725 made up of granules containing a mixture of the source powders. The composite powder is then used as an additive manufacturing feedstock material in an additive manufacturing process that directly produces a fully dense sintered article 740 from the composite powder. A deoxygenation operation 750 can be applied to the composite, the sintered article, or both to reduce the oxygen concentration.
[0046]The gold source powder, titanium source powder, powder mixture, consolidation, and sintering are described in more detail below.
Powder Mixture
[0047]In one aspect, a blended elemental approach can be used where gold source powder, titanium source powder, and other optional dosing elements can be mixed together to form a part or form. A powder mixture of a gold source powder and a titanium source powder can be prepared. The titanium present in the mixture, and sometimes other secondary alloying elements, can be deoxygenated, either before or after mixing. This can be done under an elevated temperature and in a hydrogen-containing atmosphere to produce a low-oxygen powder mixture. The powder mixture can be consolidated to form a consolidated body. The consolidated body can be at least partially sintered to form a sintered article.
[0048]Deoxygenation can be accomplished through any suitable technique. For example, the titanium powder can be deoxygenated at a deoxygenation temperature under a hydrogen-containing atmosphere to produce a deoxygenated powder. In some examples, the deoxygenation process can include the hydrogen-assisted magnesiothermic reduction (HAMR) process as described in U.S. Pat. No. 9,669,464, which is incorporated herein by reference. In some cases, the deoxygenation can be applied to powders prior to consolidation, to a consolidated (i.e. porous green body) article, and/or to a sintered article. Deoxygenation can be accomplished by exposing the material to a deoxygenation agent such as, but not limited to, Mg, Ca, hydrides thereof, chlorides thereof, and the like. Such deoxygenation can be performed at elevated temperatures and controlled atmosphere (i.e. with or without hydrogen and in oxygen-free or low oxygen environments).
[0049]In certain examples, a HAMR process can be used for deoxygenation. This process can include contacting the titanium powder with a magnesium deoxygenation agent and heating under a hydrogen atmosphere for a period of time. The magnesium deoxygenation agent can be magnesium metal, MgH2, or a combination thereof. The hydrogen atmosphere can be provided by flowing hydrogen gas over the titanium powder, or by hydrogen evolving from MgH2, or by hydrogen evolving from TiH2 present in the titanium powder, or a combination thereof. The titanium powder and magnesium deoxygenation agent can be heated to a deoxygenation temperature for a deoxygenation time. In some examples, the deoxygenation temperature can be from 400° C. to 1200° C., or from 400° C. to 900° C., or from 700° C. to 1200° C., or from 600° C. to 800° C., or from 700° C. to 900° C. The magnesium deoxygenation agent can react with oxygen in the powder to form MgO. The MgO can be removed by leaching using a weak acid in some examples. The process of heating the titanium powder under a hydrogen atmosphere can convert at least a portion of the titanium to TiH2. Therefore, after the oxygen has been removed by reacting with the deoxygenation agent, the powder can be dehydrogenated to convert TiH2 to titanium metal in some examples. The dehydrogenation can be performed by heating the powder at a dehydrogenation temperature, such as above 400° C., or from 400° C. to 900° C., or from 400° C. to 700° C., or from 400° C. to 600° C. The powder can be placed under vacuum or a non-hydrogen atmosphere, such as argon, during the heating. This heating can continue for a sufficient time to convert the TiH2 to titanium metal.
[0050]It is noted that the HAMR deoxygenation process or another deoxygenation process can be used at various points in the methods described herein. For example, the deoxygenation process can be used to deoxygenate the titanium source powder, the powder mixture after the various metal source powers have been mixed together, a composite metal powder if such a composite metal powder is formed, the consolidated body, the sintered article, or any combination of these. Thus, in some examples multiple deoxygenation operations can be performed.
[0051]The gold source powder can be a gold powder which is commercially pure. In other cases, a gold alloy may be strategically selected to achieve certain final part properties. Typically, gold powder can have a purity of greater than about 99.6 wt % and in some cases greater than 99.0 wt %, and in other cases greater than 99.9 wt %. The gold source powder can have a mean particle size ranging from a D10 of 1 μm to a D90 of 150 μm, or in some cases a D90 of 10 μm, or in some cases a D90 of 15 μm, or in some cases a D90 of 25 μm, or in some cases a D90 of 45 μm, or in some cases a D10 of 20 μm to a D90 of 45 μm, or in some cases a D10 of 5 μm to a D90 of 25 μm, or in some cases a D10 of 5 μm to a D90 of 20 μm or in some cases a D10 of 5 μm to a D90 of 15 μm, or in other cases a D10 of 1.5 μm to a D90 of 3.0 μm. Smaller particle sizes tend to result in finer grains while larger sizes result in larger grain sizes, depending on sintering and consolidation conditions.
[0052]The titanium source powder can be a commercially pure titanium (cp-Ti), titanium hydride, or another titanium alloy to achieve certain final properties. In one example, cp-Ti can be useful to reduce impurities for production of high-quality jewelry or biologically compatible surface. Generally, the titanium source powders can be provided at a particle size which is the same, substantially the same, or within about 5% of an average particle size of the gold source powder. However, in some cases, the average particle size of the titanium source powder can be more than 5% greater than the average particle size of the gold source powder. In other cases, the average particle size of the titanium source powder can be less than 5% less than the average particle size of the gold source powder. In some cases, bi-modal or multi-modal particle size distributions may be used of one or more or all of the blended constituent powders to improve density in the final part. In some cases, the titanium source powder can have an average particle size can be a D90 of about 45 μm, in other cases from a D10 of 10 μm to a D90 of 44 μm, and in other cases a D90 of 25 μm, and in other cases a D10 of 5 μm to a D90 of 25 μm, and in other cases a D90 of 20 μm, and in other cases a D10 of 5 μm to a D90 of 20 μm, and in other cases a D90 of 15 μm. In further examples, a bi-modal or tri-modal, or multi-modal powder size distribution may be used where a coarser distribution such as a D10 of 100 μm to a D90 of 150 μm is blended in with one or more finer distributions or mixture of more than one finer distribution. In other examples, the coarser powder size distribution may be a D10 of 75 μm to a D90 of 100 μm, or a D10 of 75 μm to a D90 of 150 μm, or a D10 of 45 μm to a D90 of 75 μm, or a mixture of these size distributions.
[0053]Additional metal source powders can be included in order to adjust properties of the gold-titanium alloy during processing and of the final alloy product. In some cases, the additional metal powders can function as grain control elements which either inhibit or otherwise mitigate grain growth during consolidation and sintering. Furthermore, such additional metal powders can provide improved tensile strength, increased shine, reduced brittleness, inhibition of crack propagation, adjustment of working temperatures, increased hardness, and reduced shape memory effects characteristic of many gold-titanium alloys. Non-limiting examples of suitable additional metal powders can include secondary alloying metal powders, grain refining metal powders, and the like. Non-limiting examples of secondary alloying metal powders can include Ag, Al, V, Fe, Co, Ba, Y, Zr, Ir, Ta, W, Ir, Ru, Re, Nb, Pd, Pt, Ni, Rh, Cr, C, Mn, Cu, Zn, B, Si, Ge, Sn, Sb, In, Mo, mixtures thereof, and the like.
[0054]Notably, the source powders can be purchased at a desired particle size, or can be processed to achieve a desired target particle size. For example, larger particles can be crushed, milled, and/or sieved to a target particle size. Characterization of the feed powder can include particle size distribution (including relative size between the two metals), flowability, apparent density, tap density, chemical composition, freedom from foreign inclusions, and other tests as needed.
[0055]The powder mixture can include the gold source powder at less than 10%, or about 10% to about 25%, or about 25 wt % to about 80 wt %, or equal to or above 50 wt %, or about 50 wt % to about 75 wt %, or about 65 wt % to about 75 wt %, or about 70 wt % to about 75%, or about 70% to about 80 wt %.
[0056]The powder mixture can include the Ti source powder at less than 20 wt %, or about 20 wt % to about 50 wt %, or about 20 wt % to about 35 wt %, or about 20 wt % to about 30 wt %, or from about 22 wt % to about 28 wt %, or from about 25 wt % to about 28 wt %.
[0057]In some cases, the total of alloying elements, other than titanium and gold, may be equal to or less than 10%, or equal to or less than 5%, or equal to or less than 1 wt % of the final alloy composition, and in some cases about equal to or less than 0.5 wt % about equal to or less than 1.5 wt %, and in some cases about 1 wt % to about 2 wt %, and in some cases about 2 wt % to about 4 wt %, and in some cases equal to or more than 4 wt %. In some cases, the gold-titanium alloy can be substantially free of secondary metals (i.e. other than gold and titanium). In one example, 18 carat gold alloy can be produced by using equal to or more than 75 wt % of gold with 25 wt % titanium (i.e. optionally with a small excess such as 0.5% gold to achieve a final gold content of at least 75 wt %). In other cases, secondary metal source powders can be present up to about 50 wt %, and in some cases up to 25 wt %, and in other cases up to about 10 wt %. These source powders can be thoroughly mixed together to form a homogeneous mixture.
[0058]In some examples, the powder mixture as a whole can have an average particle size from a D10 of 1 μm to a D90 of 150 μm, or in some cases a D90 of 10 μm, or in some cases a D90 of 15 μm, or in some cases a D90 of 25 μm, or in some cases a D90 of 45 μm, or in some cases a D10 of 20 μm to a D90 of 45 μm, or in some cases a D10 of 5 μm to a D90 of 25 μm, or in some cases a D10 of 5 μm to a D90 of 20 μm or in some cases a D10 of 5 μm to a D90 of 15 μm, or in other cases a D10 of 1.5 μm to a D90 of 3.0 μm. In certain examples, the powder mixture can be used to prepare a consolidated body by pressing. In these cases, the average particle size of the powder mixture can be a D90 of 25 μm, or a D10 of 5 μm to a D90 of 20 μm, or a D10 of 5 μm to a D90 of 25 μm, or a D90 of 45 μm. In further examples, the powder mixture can be utilized in a binder jet additive manufacturing process to form the consolidated body. In these examples, the average particle size of the powder mixture can be a D90 of 25 μm, or a D10 of 5 μm to a D90 of 20 μm, or a D10 of 5 μm to a D90 of 25 μm, or a D90 of 45 μm, or a D10 of 20 μm to a D90 of 45 μm. In further examples, the powder mixture can be used in a laser bed fusion additive manufacturing process. In these examples, the average particle size of the powder mixture can be a D10 of 20 μm to a D90 of 45 μm, a D10 of 25 μm to a D90 of 45 μm, or a D10 of 20 μm to a D90 of 53 μm.
[0059]The powders can be mixed well using a variety of mixing equipment types to achieve homogeneity, and may also be mixed at various ranges of higher energy to mechanically alloy the constituent powders to the degree desired. In some cases, particle sizes of the constituent powders can be strategically varied to achieve certain particular results.
Consolidation
[0060]The powder mixture can be consolidated to form a consolidated body prior to sintering in order to increase densification and reduce porosity. In some cases, the consolidated body can be a shaped body as a net shape, or near-net shape, in order to reduce waste. In other cases, a blank or bulk body can be formed which is then later machined or formed into a desired shape.
[0061]In either case, the consolidation can include a pressing stage. Non-limiting examples of suitable pressing can include uniaxial pressing, hot pressing, cold isostatic pressing, centrifugal casting, slip casting, powder extrusion or other plastic deformation approach, gravity casting, rolling, iso-static molding, explosive compacting, or combination or variations of these processing approaches. In one aspect, the pressing can be a uniaxial pressing.
[0062]In some cases, impurities or binders can be present in the powder mixture. Accordingly, the consolidation can optionally include a debinding stage in which the powder mixture is subjected to heating sufficient to drive off volatile impurities, decompose binder, and reduce organic content.
Sintering
[0063]In order to further reduce porosity and, in some cases, to adjust or control microstructure of the alloy, the consolidated body can be at least partially sintered to form a sintered article. Sintering can be accomplished through any method for heating a consolidated part to induce solid-state diffusion, not limited to a sintering furnace, direct current sintering or any other form of current-assisted sintering, microwave sintering, hot isostatic pressing or any other sintering where pressure variations are used to assist in sintering. Sintering can be performed to densify the body to achieve a density equal to or greater than 90%, or equal to or greater than 95%, or equal to or greater than 98% or equal to or greater than 99%, depending on the initial powder average particle size, particle size distribution, sintering times, sintering temperatures, sintering pressure, and the like. Sintering temperature can vary considerably. However, as a general guideline, sintering temperatures can range from 800° C. to 1400° C., in some cases 800° C. to 1000° C., in some cases 900° C. to 1000° C., in some cases 900° C. to 1100° C., in some cases 1000° C. to 1100° C., in some cases 1000°° C. to 1200° C., in some cases 1100° C. to 1200° C., in some cases 1100° C. to 1300° C., in some cases 1200°° C. to 1300° C., in some cases 1200° C. to 1400° C. Temperature ramping and cooling rates can be strategically adjusted to achieve desired microstructures, and hold times and temperatures can also be adjusted to achieve desired homogeneity, density, etc. For example, an oil or gas quenching method may be used, or any other approach to rapidly cool the consolidated body.
Deoxygenation and Post-Processing
[0064]As mentioned above, deoxygenation can be performed on the source powders, the consolidated body, the sintered article, or a combination thereof. In some examples, the sintered article can be deoxygenated at a deoxygenation temperature under a hydrogen-containing atmosphere to produce a deoxygenated article. This deoxygenation can be performed using the HAMR process described in U.S. Pat. No. 9,669,464, which is incorporated herein by reference. In one aspect, the deoxygenating includes heating the sintered article in the presence of a magnesium deoxygenation agent at a deoxygenation temperature. The magnesium deoxygenation agent can include at least one of metallic magnesium, magnesium hydride, magnesium chloride, and magnesium bromide. The deoxygenation temperature can generally range from 550° C. to 900° C.
[0065]Deoxygenation produces magnesium oxide which can be removed and recycled. Removed oxygen can most often include oxygen dissolved in solid solution, although some oxygen can be moved by reduction of a corresponding metal oxide. For example, titanium has an extremely high affinity of oxygen and will oxidize to titanium oxide upon exposure to oxygen. As a result, deoxygenation can remove any such inadvertently formed oxides, along with interstitial dissolved oxygen.
[0066]These processes can produce deoxygenated articles having improved properties. For example, in some cases, the deoxygenated article can have a grain size less than 10% greater than a starting grain size of the powder mixture. In a further example, the deoxygenated article can have no more than 10% of grain sizes (as measured in cross-section diameter in any direction in the plane) below or above a certain size; for example, in some cases a deoxygenated article may have no more than 10% of grain sizes below or above (respectively) the values of 10 μm to 100 μm, and in some cases 5 μm to 10 μm, and in some cases 5 μm to 15 μm, and in some cases 10 μm to 20 μm, and in some cases 10 μm to 50 μm, and in other cases 11 μm to 25 μm, and in yet other cases 50 μm to 90 μm. In other examples, no more than 10% of grain sizes may be smaller than 5 μm, and in some cases smaller than 10 μm. Hardness can also be improved through these processes. In one example, the deoxygenated article can have a hardness greater than 400 Hv, and in some other cases 250 Hv to 350 Hv, and in other cases 300 Hv to 400 Hv, and in other cases 350 Hv to 450 Hv, and in other cases 400 Hv to 500 Hv, and in other cases 500 to 600 Hv, and in other cases 600 to 700 Hv, and yet in other cases 700 to 800 Hv. In another aspect, the deoxygenated article can have a density as low or lower than 11 g/cc for select compositions to achieve an 18 carat gold alloy, or range up to 15 g/cc or higher for other compositions. The selection of a composition is made based on meeting the gold purity level (in terms of carats) and optimizing for a lower density alloy for the comfort of the customer wearing a luxury product produced with the alloy. Testing of properties in a consolidated part can include microstructure, hardness, density, surface finish, and chemical composition, for example.
[0067]Additional post-processing stages can be used to refine the produced alloy. If a deoxygenation operation is performed on the sintered article, then these additional post-processing stages can be performed before or after the deoxygenation. For example, a grain refinement stage can be used to further adjust properties of the article. In one example, a heat-treating step can be used in conjunction with a surface treatment alloy to allow diffusion of a secondary metal just near the surface to a desired depth. In another example, the produced article can be machined, cut and/or polished to final specifications. Optional heat treatment strategies may be employed, including (but not limited to) quenching, annealing, stress-relieving, aging, precipitation hardening, and any combination of parameters for heating rate, hold times and temperatures, cooling rates, surface treatments, etc., and any number of process gases or vacuum conditions are used, or combination of gases are used simultaneously or in sequence and at different temperatures or pressures.
Composite Metal Powder
[0068]In a related variation, a composite metal powder, or pre-alloyed powder, can be prepared which includes composite granules formed of a gold source powder and a titanium source powder within the composite granules. The pre-alloying powder can be prepared with spray drying, granulation drums, static bed drying, or another granulation approach to form an engineered, pre-alloy powder with homogeneous particle chemistry. A non-limiting example of one granulation approach can include a spherical metal powder production process described in U.S. Pat. No. 10,130,994 which is incorporated herein by reference.
[0069]In a particular example, the metal source powders, including gold source powder, titanium source powder, and any alloying metal powders, can be mixed to form a powder mixture. The powder mixture can optionally be milled, such as by ball milling, to reduce the particle size of the powder mixture. The powder mixture can also be mixed with a binder and a solve