Patent Application
20240261854
The following publications are hereby incorporated herein by reference:
Gold-titanium alloys have been used in high-end luxury goods, jewelry, dentistry, horology, ceramics, and other industries. These alloys can be desirable due to their gold appearance and high scratch resistance. The production of gold-titanium articles has been challenging because of unique characteristics of the gold-titanium alloy system that can cause segregation of composition, coarse grain structures, high-cost of processing, and the high cost of machining waste of expensive gold. As an example, poor uniformity in chemistry and large columnar grains can occur during solidification when using casting methods for gold-titanium alloys. In some cases, other elements (e.g. Ta, W, Co, Ir, Ru, Re, Mo) have been added as grain refiners, and only a small set of compositions has been found to provide adequate grain size results. The selection of additional elements can also be constrained by biocompatibility of the additional elements when the gold-titanium alloy article is wearable, such as in luxury goods applications.
Certain compositions of gold-titanium alloys have shown exceptional hardness properties, low densities, and good biocompatibility. One reported alloy composition had the formula Ti1-xAux where x was optimized for low density and high hardness to be between 0.15 and 0.4 (see Svanidze, High hardness in the biocompatible intermetallic compound β-Ti3Au, Sci. Adv., 2016, pages 1-6, which is hereby incorporated herein by reference).
International Publication WO 2022/148817 A1 to Guidoux et al. describes achievement of an alloy with two or three primary elements that was easy to shape with mechanical deformation, because its shape memory effects were lower than what is traditionally seen in Au—Ti alloys.
However, regardless of these advances, casting approaches utilize high temperatures to melt the constituent metals, and tend to produce chemical segregation, large columnar grains, shape-memory effects in certain alloy compositions, and high amounts of waste in machining to achieve final part dimensions. Processing using a melt approach can result in non-uniform melting, where exterior regions of the melt will solidify first. This creates a stable base from which metal crystals can grow. This results in columnar grain structures which grows from the solidified exterior towards the inner molten regions of the bulk during solidification. Also, dissimilar melting points, dissimilar solubility limits of the metals in the alloy, and various phase changes that can occur at different compositions and temperatures during cooling can lead non-homogeneous regions in the cast part.
Large grains in alloy ingots can be refined through hot-working of the solid to break-up the grains and achieve recrystallization. However, gold-titanium alloys often suffer from shape memory effects which make this effort difficult, and there are yield losses on the surfaces. Any yield loss in a gold-titanium alloy is costly given the high price of gold. Additionally, machining of a solid, blocky form to a final part can lead to significant waste, which can also be very expensive.
A novel approach for low-cost production of gold-titanium alloy articles can involve gold and titanium powders and sintering to form sintered articles. The gold and titanium powders can include pre-alloy powders and/or blends of elemental gold and titanium powders. Additional benefits can be achieved by deoxygenation processing. The novel approaches described herein can be enhanced by the application of deoxygenation technology, which opens the door to lower-cost production of gold-titanium parts with high uniformity in chemical segregation, lower oxygen values, fine grained microstructure, and limited waste.
In one example, a method of making a gold-titanium alloy can include preparing a powder mixture that includes a gold source powder and a titanium source powder. The powder mixture can be consolidated to form a consolidated body. The consolidated body can be at least partially sintered in vacuum or a reducing atmosphere to form a gold-titanium alloy sintered article.
In another example, a method of producing a gold-titanium alloy can include preparing a composite metal powder having composite granules that include a gold source powder and a titanium source powder within the composite granules. The composite metal powder can be consolidated to form a consolidated body. The consolidated body can be at least partially sintered to form a sintered article. The composite metal powder, the consolidated body, and/or sintered article can be deoxygenated at a deoxygenation temperature under a hydrogen-containing atmosphere to reduce an oxygen content.
The present disclosure also describes composite metal powders that can be used in these methods. In one example, a composite metal powder can include granules including a gold source powder and a titanium source powder. A weight ratio of gold powder to titanium powder in the granules can be from 1:5 to 5:1, or from 1:4 to 4:1, or from 1:3 to 4:1, or from 1:1 to 4:1, or from 2:1 to 3:1, or from 2.5:1 to 3:1. A variation of the weight ratio among the granules can be less than 10%.
There has thus been outlined, rather broadly, the more important features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.
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.
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.
In describing and claiming the present invention, the following terminology will be used.
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.
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.
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%.
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.
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.
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.
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.
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.
Another example method 200 of making a gold-titanium alloy is illustrated in
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.
Another example method of making a gold-titanium alloy is illustrated in a flowchart in
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.
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.
Another example method is illustrated in a flowchart in
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.
The gold source powder, titanium source powder, powder mixture, consolidation, and sintering are described in more detail below.
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.
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).
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.
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.
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.
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.
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.
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.
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 %.
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 %.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 solvent to form a slurry. The slurry can be granulated to form spherical granules, where each granule includes the binder and an agglomeration of powder particles from the powder mixture. In some cases, the granules can be formed by spray drying the slurry to form the spherical granules. The solvent can evaporate as the slurry is sprayed, causing spherical droplets of slurry to become dry granules.
The granules can be debinded in further examples. Debinding the granules can remove the binder from the granules, leaving behind the metal powder particles. In certain examples, debinding can be accomplished by heating the granules to a debinding temperature at which the binder can evaporate, chemically decompose, combust, or otherwise be removed. The debinding temperature can be from 50° C. to 400° C. in some examples, or from 150° C. to 350° C. in other examples.
The granules can also be sintered or partially sintered as individual, separate granules. In other words, the granules can be sintered or partially sintered so that the particles of source metal powder with each individual granule are sintered to each other, but the individual granules remain separate from other granules. In some cases, the sintering can also cause binder to be removed from the granules, so that the debinding and sintering occur at the same time. In other examples, debinding can be performed first and then sintering can be performed after debinding as a separate step. The sintering can be performed in a reducing or inert atmosphere, such as vacuum, argon, hydrogen, nitrogen, or combinations thereof. The sintering can include heating the granules to a sintering temperature from about 700° C. to about 1400° C., and in some cases 900° C. to about 1000° C. The granules can be heated at the sintering temperature for a sintering time from about 1 second to about 100 hours, or less than 24 hours, or 30 minutes to 1 hour. After the sintering or partial sintering, the densification of the granules can be from about 60% to about 80%, in some examples.
In another example, the partial sintering can proceed until the debinded granules are fully sintered while retaining frangibility and/or separability. For example, sintered granules can fuse together at contact points between the granules but the granules retain unfused surface area sufficient to allow individual granules to be recovered. Typically, an unfused surface area of at least about 30% will allow the sintered frangible body to be crushed and individual granules recovered. In some cases, unfused granule surface area can be substantially 100% such that the sintered granules are not connected and are a loose collection of independent granules. Accordingly, sintering of the debinded granules can also be performed until each sintered granule is substantially free from bonding to each other.
The composite metal powder as a pre-alloy powder precursor material can be granulated into spherical or angular powder of a desired particle size of such as 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 D50.
A spherical or angular powder can be formed using a granulation and sintering approach after which the engineered powder can be consolidated to a part or form. The pre-alloyed spherical or angular powder, comprised of a gold source powder and a commercially pure (CP) titanium powder, and one or more other element additions to target certain properties, can be deoxygenated, where the titanium powder, and in some cases other element additions, are deoxygenated. In some cases, the deoxygenation can be performed at a temperature under a hydrogen-containing atmosphere to produce a low-oxygen Au—Ti—X alloy powder. The powder mixture can be consolidated to form a consolidated body as with the previously discussed variation.
The consolidated body can be at least partially sintered to form a sintered article, again in the same general manner as previously discussed with respect to a simple powder mixture of source powders. Further, the sintered article can be deoxygenated depending on a desired final oxygen content.
The pre-alloying approach can lead to high oxygen levels from the titanium portion of the alloy. Thus, hydrogen assisted magnesiothermic reduction and deoxygenation as described herein may be employed to reduce these oxygen levels to achieve desired chemical and phase compositions. This approach also allows for recycling of most, if not all, scrap by milling the scrap into the desired powder particle size without having to separate component metals.
For spherical pre-alloyed powder, a laser powder bed fusion (LPBF) additive manufacturing process can be used to form the shaped body. In this case, powder particles can be fully melted or partially melted during printing, and no further sintering is required, however in some cases a hot isostatic pressing treatment may be applied to achieve a higher part density. In this case, the melting is limited to a localized region where the laser is rastering at a given moment, after which the localized molten pool very quickly solidifies—resulting in fine grain structures with typically high stresses that can be reduced with stress-relieving heat treatment upon completion of the print.
When LPBF is used, or any other process that forms the shape of the final article and sinters the metal particles simultaneously, the consolidation step and the sintering step can occur at the same time. Thus, although consolidation and sintering are referred to separately in some examples herein, in certain examples these operations can be performed simultaneously. In particular, a consolidated body can be formed and the consolidated body can be sintered simultaneously, in a single step. In other examples, consolidation can be performed first to form a consolidated body, and the consolidated body can subsequently be sintered in a separate step.
In another alternative, a green shaped body can be formed from a pre-alloyed powder by binder jet printing, where a green part is intricately produced and held together with a binder, after which the binder can be removed and the part densified in a debind and sinter step. This process can be lower cost with higher production rates than LPBF, though it can involve shrinkage and distortion during sintering.
In another alternative, a green shaped body can be formed from a pre-alloyed powder using a traditional powder metallurgy (PM) approach such as uniaxial pressing, hot pressing, cold isostatic pressing, metal injection molding, powder injection molding, centrifugal casting, slip casting, powder extrusion or other plastic deformation approach, gravity casting, rolling, iso-static molding, explosive compacting, or any combination or variations of these and other powder consolidation processing approaches.
In still another related variation, a method of producing a gold-titanium alloy can include preparing an alloy powder including a gold source and a titanium source. The alloy powder can be consolidated to form a consolidated body. The consolidated body can then be at least partially sintered to form a sintered article. In this variation, the method can be substantially free of melting. Further, the alloy powder can be provided as either a powder mixture a gold source powder and a titanium source powder, or as a composite pre-alloyed powder. Specifically, the alloy powder can be a composite metal powder having composite granules including a gold source powder and a titanium source powder within the composite granules.
As used herein, “melting” refers to heating at a temperature and time sufficient to cause formation of liquid of the entire solid powders. Melting is different from sintering and other high temperature processes which result in either melting of particle surfaces rather than also particle cores, or solid-state diffusion of atoms which can cause grain growth and/or diffusion of alloying metals within a primary metal.
In each of the above variations, benefits and advantages can include producing a part with a high uniformity in chemical segregation. Further, a finer grained microstructure can be produced for superior properties, which can be refined by adjusting sintering and/or heat treatment parameters. These approaches can also avoid waste by producing near-net-shape parts or forms. The approaches also provide a low-cost processing route made possible by the HAMR technology.
The limited scrap from the machining of near-net-shape parts can be recaptured and reused, where any high-oxygen titanium constituent (and in some cases other alloying elements present) may be deoxygenated using HAMR technology. This cuts down on costs due to yield losses, and reduces environmental impact by providing a closed recycling loop.
These approaches also allow production of a low-cost blended elemental Au—Ti alloy part (with zero or one or more other elemental additions), with low oxygen levels in the Ti-constituent of the part, and throughout the sintered article. Similarly, these approaches allow production of a low-cost pre-alloyed Au—Ti powder (with zero or one or more other elemental additions), with oxygen levels in the Ti-constituent of the powder and other oxygen-containing components, from which a low-cost, near-net-shape part may be produced using any number of powder metallurgy and additive manufacturing technologies.
A mass of 6 grams of gold powder, with a purity of greater than 99.6 wt %, and a particle size ranging from a D10 1.5 to a D90 of 3.9 μm, were mixed with commercially pure titanium powder at a ratio of Au—Ti=75:26. The powders were mixed well and ten die-pressed into a small, cylindrical puck. The puck had a gold lustrous appearance before sintering. The puck was sintered at 1200° C. for several hours to achieve homogeneity in composition, after which the density was measure by pycnometer to be 10.58 g/cm3. The Vickers Hardness value (at 5 kg, 5 see) was measured at 354.3±3.8, as an average over 3 measurements. After sintering, but before polishing, the puck had a more dull, gray appearance.
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While the flowcharts presented for this technology may imply a specific order of execution, the order of execution may differ from what is illustrated. For example, the order of two more blocks may be rearranged relative to the order shown. Further, two or more blocks shown in succession may be executed in parallel or with partial parallelization. In some configurations, one or more blocks shown in the flow chart may be omitted or skipped. Any number of counters, state variables, warning semaphores, or messages might be added to the logical flow for purposes of enhanced utility, accounting, performance, measurement, troubleshooting or for similar reasons.
Reference was made to the examples illustrated in the drawings and specific language was used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Alterations and further modifications of the features illustrated herein and additional applications of the examples as illustrated herein are to be considered within the scope of the description.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more examples. In the preceding description, numerous specific details were provided, such as examples of various configurations to provide a thorough understanding of examples of the described technology. It will be recognized, however, that the technology may be practiced without one or more of the specific details, or with other methods, components, devices, etc. In other instances, well-known structures or operations are not shown or described in detail to avoid obscuring aspects of the technology.
Although the subject matter has been described in language specific to structural features and/or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.
The technology described herein can include the following enumerated examples:
This application claims priority to U.S. Provisional Patent Application No. 63/443,149, filed on Feb. 3, 2023, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63443149 | Feb 2023 | US |
