Degassing treatment of nanophase separated powders in hydrogen-containing atmospheres

Abstract

Removal of gas-generating species from the powder, which can be accomplished before sintering occurs, can reduce or eliminate gas generation in dense bodies that can lead to swelling or loss of density.

Description

[Technical field]

[0001] Priority claim This application claims priority to U.S. Provisional Patent Application No. 63 / 310,444, filed February 15, 2022, which is incorporated by reference in its entirety.

[0002] Government Sponsorship Statement This invention was made with Government support under Grant No. 80MSFC19C0050 awarded by the NASA Goddard Space Flight Center. The Government has certain rights in this invention.

[0003] The present invention relates to phase separated powders and methods for processing same. [Background technology]

[0004] Sintered nanocrystalline materials are often subjected to pressure or other post-sintering processing techniques to achieve a denser material. Summary of the Invention

[0005] In one aspect, a method of reducing outgassing during sintering of a metal alloy powder may include providing a mechanically alloyed metal alloy powder, annealing the metal alloy powder at an annealing temperature below a sintering temperature, where the annealing of the metal alloy powder is performed in an atmosphere comprising hydrogen, or the metal alloy powder comprises an oxygen getter, or both, and sintering the metal alloy powder at a sintering temperature to reduce outgassing during sintering.

[0006] In certain circumstances, the method may include pressing the annealed metal alloy powder to form a green body prior to sintering.

[0007] In certain circumstances, the method may include pressing the metal alloy powder to form a compact prior to annealing.

[0008] In certain circumstances, the metal alloy powder may be a nano-phase separated powder.

[0009] In certain circumstances, the metal alloy powder may include additives.

[0010] In certain circumstances, the additive may include an organic material.

[0011] In certain circumstances, the metal alloy powder may include nickel, chromium, iron, copper, vanadium, molybdenum, tungsten, silver, zirconium, or combinations thereof.

[0012] In certain circumstances, the metal alloy powder may include a ternary nano-phase separated powder.

[0013] In certain circumstances, the metal alloy powder may include a quaternary nano-phase separated powder.

[0014] In certain circumstances, the oxygen getter may include alloying elements that have a strong tendency to form oxides.

[0015] In certain circumstances, the oxygen getter may include zirconium, chromium, vanadium, manganese, or combinations thereof.

[0016] In certain circumstances, the oxygen getter concentration can be from about 1 atomic % to about 4 atomic % of the alloy.

[0017] In certain circumstances, the annealing temperature may be about 200°C to 400°C.

[0018] In certain circumstances, the sintering may include nano-phase separation sintering.

[0019] In certain circumstances, the grain size of the metal alloy powder and the grain size of the sintered powder are substantially the same.

[0020] In another aspect, the metal alloy powder for sintering can include a mechanically alloyed powder having a reduced amount of gas-evolving species compared to the amount of gas-evolving species in the mechanically alloyed powder prior to annealing in a hydrogen atmosphere.

[0021] In certain circumstances, the mechanically alloyed powder may be a nano-phase separated powder.

[0022] In certain circumstances, the mechanically alloyed powder may include an oxygen getter.

[0023] In certain circumstances, the mechanically alloyed powder may include nickel, chromium, iron, copper, vanadium, molybdenum, tungsten, silver, zirconium, or combinations thereof.

[0024] In certain circumstances, the mechanically alloyed powder can be a ternary nano-phase separated powder or a quaternary nano-phase separated powder.

[0025] In another aspect, a method of forming a sintered alloy can include annealing a nano-phase separated metal alloy powder in the presence of hydrogen, and sintering the nano-phase separated metal alloy powder to form a sintered alloy article comprising nickel and having a relative density of at least 80%.

[0026] In certain circumstances, the sintered alloy article may include dispersed oxide.

[0027] In some circumstances, the annealing and sintering may be carried out in a single step.

[0028] In some circumstances, annealing and sintering may be carried out in successive steps.

[0029] In another aspect, a sintered body can include the powders described herein.

[0030] Other aspects, embodiments, and features will become apparent from the following description, the drawings, and the claims. [Brief description of the drawings]

[0031] [Figure 1A] FIG. 1A is a schematic diagram illustrating nano-phase separation sintering, including phase separation, necking, sintering, and densification. [Figure 1B] FIG. 1B shows the phase diagram. [Figure 1C] FIG. 1C is a schematic diagram illustrating one example of the general process described herein. [Figure 2A] FIG. 2A shows the Ni-Cu phase diagram. [Figure 2B] FIG. 2B is a graph showing the behavior of the system. [Diagram 3] FIG. 3 shows the phase diagram. [Figure 4A] FIG. 4A is a graph showing densification rate. [Figure 4B] FIG. 4B is a graph showing the change in relative density. [Figure 5A] FIG. 5A shows the Ni—Cr phase diagram. [Figure 5B] FIG. 5B shows the Cu—Cr phase diagram. [Figure 6A] FIG. 6A shows the Ni-Cu phase diagram at 5 at. % Cr. [Figure 6B] FIG. 6B shows the Ni-Cu phase diagram at 10 at. % Cr. [Figure 6C] FIG. 6C shows the Ni-Cu phase diagram at 15 at. % Cr. [Figure 6D] FIG. 6D shows the phase diagram for 60 atomic % Ni and 15% Cr. [Figure 6E] FIG. 6E is a table showing the composition of the stable phase at 550° C. [Figure 6F] FIG. 6F is a graph showing the temperature dependence of densification at 5° C. / min to 1200° C. and cooling at 40° C. / min. [Figure 7A] FIG. 7A shows the Ni-Fe phase diagram. [Figure 7B] FIG. 7B shows the Cu—Fe phase diagram. [Figure 8A]FIG. 8A shows the Ni—Cu phase diagram at 5 at. % Fe. [Figure 8B] FIG. 8B shows the Ni—Cu phase diagram at 20 at. % Fe. [Figure 8C] FIG. 8C shows the Ni—Cu phase diagram at 42 at. % Fe. [Figure 8D] FIG. 8D shows the Ni—Cu phase diagram at 42 at. % Fe. [Figure 8E] FIG. 8E is a table showing the composition of the stable phase at 550° C. [Figure 8F] FIG. 8F is a graph showing the temperature dependence of densification at 5° C. / min to 945° C. and cooling at 40° C. / min. [Figure 8G] FIG. 8G is a graph showing the change in relative density over time when heated at 5° C. / min. [Figure 8H] FIG. 8H is a graph showing the temperature dependence of densification when heated at 10° C. / min to 1000° C. and cooled at 40° C. / min. [Figure 8I] FIG. 8I is a graph showing the change in relative density over time when heated at 5° C. / min to a final relative density of 0.5864%. [Figure 8J] FIG. 8J is a graph showing the temperature dependence of densification when heated at 15° C. / min to 1000° C. and cooled at 40° C. / min. [Figure 8K] FIG. 8K is a graph showing the change in relative density over time when heated at 15° C. / min to a final relative density of 0.5477%. [Figure 8L] FIG. 8L is a graph showing the temperature dependence of densification when heated to 1000° C. at 20° C. / min and cooled at 40° C. / min. [Figure 8M] FIG. 8M is a graph showing the change in relative density over time when heated at 20 degrees / minute to a final relative density of 0.4276%. [Figure 8N] FIG. 8N is a graph showing the temperature dependence of densification at 5° C. / min to 1100° C. and cooling at 40° C. / min. [Figure 8O] FIG. 8O is a graph showing the change in relative density versus temperature when heated at 5° C. / min. [Figure 8P] FIG. 8P is a graph showing the change in relative density over time when heated at 5° C. / min. [Figure 8Q] FIG. 8Q is a graph showing the temperature dependence of densification at 10° C. / min to 1100° C. and cooling at 40° C. / min. [Figure 8R] FIG. 8R is a graph showing the change in relative density versus temperature when heated at 10° C. / min. [Figure 8S] FIG. 8S is a graph showing the change in relative density over time at 15° C. / min. [Figure 8T] FIG. 8T is a graph showing the temperature dependence of densification at 20° C. / min to 1100° C. and cooling at 40° C. / min. [Figure 8U] FIG. 8U is a graph showing the temperature dependence of densification at 20° C. / min to 1100° C. and cooling at 40° C. / min. [Figure 8V] FIG. 8V is a graph showing the change in relative density over time at 20° C. / min. [Figure 9A] FIG. 9A shows the Ni—Co phase diagram. [Figure 9B] FIG. 9B shows the Cu—Co phase diagram. [Figure 10A] FIG. 10A shows the Ni—Cu phase diagram at 5 at. % Co. [Figure 10B] FIG. 10B shows the Ni—Cu phase diagram at 20 at. % Co. [Figure 10C] FIG. 10C shows the Ni—Cu phase diagram at 44 at. % Co. [Figure 11A] FIG. 11A shows the Ni-V phase diagram. [Figure 11B] FIG. 11B shows the Cu-V phase diagram. [Figure 12A] FIG. 12A shows the Ni—Cu phase diagram at 6 atomic % V. [Figure 12B] FIG. 12B shows the Ni—Cu phase diagram at 10 at. % V. [Figure 12C] FIG. 12C shows the Ni—Cu phase diagram at 13 at. % V. [Figure 12D] FIG. 12D shows the Ni—Cu phase diagram at 13 at. % V and 15 at. % Cu. [Figure 12E] FIG. 12E is a table showing the stable phases at 1150° C. [Figure 12F] FIG. 12F is a graph showing the temperature dependence of densification rate at 5° C. / min to 1200° C. and cooling at 40° C. / min. [Figure 12G] FIG. 12G is a graph showing the temperature dependence of the change in relative density. [Figure 13] FIG. 13 is a chart showing the diffusion rates and temperature ranges of the metals described herein. [Figure 14A] FIG. 14A shows the phase diagram of Fe-Cu with 40 at. % Ni, taken from the Fe database. [Figure 14B] FIG. 14B shows the phase diagram of Fe—Cu containing 40 at. % Ni, obtained from the Ni database. [Figure 14C] FIG. 14C shows the phase diagram of Fe—Cu with 40 at. % Ni, obtained from the Cu database. [Figure 14D] FIG. 14D shows the phase diagram of Fe—Cu with 40 at. % Ni, taken from the High Entropy Alloy Database. [Figure 15] FIG. 15 shows the Cr-Cu phase diagram at 60 atomic % Ni. [Figure 16] FIG. 16 shows the Co-Cu phase diagram at 40 atomic % Ni. [Figure 17] FIG. 17 shows the Cu-V phase diagram at 75 atomic % Ni. [Figure 18A] FIG. 18A is a graph showing densification after hydrogen pretreatment at different heating rates. [Figure 18B] FIG. 18B is a graph showing densification after hydrogen pretreatment at different heating rates. [Figure 18C] FIG. 18C is a graph showing densification after hydrogen pretreatment at different heating rates. [Figure 19]FIG. 19 is a graph showing the effect on density of 5 at. % Mn and 8 at. % Mn in a Ni-Fe-Cu composition. [Figure 20] FIG. 20 is a graph showing the densification behavior when a composition of 37.5 at % Ni-37.5 at % Co-20 at % Cu-5 at % Mn is heated to 1200° C. and Mn is added. [Figure 21] FIG. 21 is a photomicrograph of the composition of FIG. [Figure 22] FIG. 22 is a photomicrograph of the composition of FIG. [Diagram 23] FIG. 23 is a photomicrograph of the composition of FIG. [Figure 24] FIG. 24 is a photomicrograph of the composition of FIG. [Diagram 25] FIG. 25 is a graph showing the mechanical properties of sintered bodies containing 37.5 atomic % Ni, 37.5 atomic % Fe, 20 atomic % Cu, and 5 atomic % Mn. [Figure 26] FIG. 26 is a graph showing the mechanical properties of sintered bodies containing 37.5 atomic % Ni, 37.5 atomic % Fe, 20 atomic % Cu, and 5 atomic % Mn. [Figure 27] FIG. 27 is a graph showing the mechanical properties of sintered bodies containing 37.5 atomic % Ni, 37.5 atomic % Fe, 20 atomic % Cu, and 5 atomic % Mn. [Figure 28] FIG. 28 is a graph showing the mechanical properties of sintered bodies containing 37.5 atomic % Ni, 37.5 atomic % Fe, 20 atomic % Cu, and 5 atomic % Mn. [Figure 29A] FIG. 29A shows the phase diagram. [Figure 29B] FIG. 29B shows the phase diagram. [Diagram 30] FIG. 30 is a graph showing sintering of Mo and W base alloyed with Cr. [Diagram 31] FIG. 31 is a graph showing testing of the Mo25W15Cr sample. [Diagram 32] FIG. 32 is a graph showing densification versus time. [Figure 33A] FIG. 33A is a graph showing densification versus temperature. [Figure 33B] FIG. 33B is a graph showing the change in relative density over time. [Diagram 34] FIG. 34 is a schematic diagram showing the addition of a getter. [Diagram 35] FIG. 35 is a graph showing the swelling ratio versus Zr content. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Metal powders can be used to manufacture metal components, for example by pressing and sintering, or 3D printing / additive manufacturing. Many metal powders form gaseous products upon annealing, for example CO and CO in the presence of carbon impurities, which can slow or prevent powder consolidation and reduce the final density of the sintered microstructure.

[0033] In particular, it is difficult to remove gas-generating species from powders before sintering occurs, because gas generation in dense bodies can lead to swelling, or loss of density. As described herein, reduction treatment of powders can be a process step to provide powders with improved sinterability. The general purpose of reduction treatment is to allow rapid consolidation of powders that exhibit rapid densification by nanophase separation sintering and that otherwise tend to release fugitive gas species during the sintering process. A more specific benefit of removing undesirable interstitial impurity elements is the reduction of harmful outgassing products formed during sintering, which can accelerate the consolidation process and improve the density of the final microstructure. Low-temperature reduction of magnetite in pure H2 is described, for example, in Spreitzer, D. and Schenk, J. (2019), Reduction of Iron Oxides with Hydrogen-A Review. Steel Research Int., 90: 1900108, which is incorporated herein by reference in its entirety. What is important is that the reduction occur without nanophase separation or grain growth.

[0034] For example, the reduction of ball milled and nanophase separated powders can be carried out in an atmosphere containing hydrogen. Hydrogen is a good candidate as a shaping and reducing agent in many powder metallurgy processes. Hydrogen is known to interact with metals because it is present in abundant concentrations in the atmosphere, can easily migrate along defects in the microstructure, and can dissolve in the metal to some extent.

[0035] The treatment step may include reduction of the nanophase separated powder in an atmosphere containing hydrogen. Prior to the reduction treatment, the elemental powders may be mechanically alloyed to form a solid solution with homogeneous distribution of all elements and grain size refined to the nanometer scale.

[0036] The loose milled powder may be annealed by exposure to a reducing atmosphere at a relatively low temperature, such as 200° C.-400° C., for at least 6 hours, at least 8 hours, at least 10 hours, at least 12 hours, at least 14 hours, at least 16 hours, at least 18 hours, at least 20 hours, at least 22 hours, or at least 24 hours. For example, the powder may be annealed by exposure to a hydrogen atmosphere at a relatively low temperature, such as 250° C.-350° C., for 24 hours. Reduction may reduce the mass loss during sintering from about 2% for the as-milled powder to about 1.2-1.8% for the annealed reduced powder.

[0037] After reduction, the powder can be formed into a desired shape as a compact. On a laboratory scale, the powder can be cold pressed into a pellet, but the actual final part may vary. For example, the annealed metal alloy powder can be pressed to form a compact before sintering. In another example, the metal alloy powder can be pressed to form a compact before annealing.

[0038] The pressed shape can be heated to a desired temperature range, where rapid densification occurs via nanophase separation at lower temperatures.

[0039] Variations of these steps are also contemplated, with the reduction treatment being carried out on a pressed or molded body, or in-line with the sintering process itself, as one step in the thermal cycle used for sintering.

[0040] This method and material may have various advantages and improvements. For example, low temperature treatment in a hydrogen-containing can is suitable for reducing metal powders, producing gaseous H2O, thus avoiding the production of CO or CO2 gas released from the powder during sintering without a prior reduction step. Metal powders also often contain small amounts of contaminations such as oxygen and carbon, originating from the manufacturing process and / or from processing aids added to support the high energy milling process in preparation for the nanophase separated sintering process. Reduction treatments can reduce the extent of this undesirable impurity inclusion, leading to a cleaner final product with improved overall properties. In addition to structural properties, the significant reduction in contamination levels may facilitate and accelerate the sintering process of nanophase separated powders, improving the final density and thus the mechanical properties of the sintered parts.

[0041] Nanophase separated powders may present an additional advantage due to the large number of grain boundaries that can provide diffusion paths for hydrogen from the environmental gas into the powder. This can increase the reduction rate and reduce the overall process time and cost. Because the powders have an internal grain structure on the order of a few nanometers, the bulk diffusion distance is several orders of magnitude smaller, making the ball-milled powders highly suitable for reduction in hydrogen-containing gases.

[0042] Another factor is that nanocrystalline powders have a large proportion of grain boundaries, which allows for relatively fast diffusion of H2. H2 diffuses faster than an atmosphere containing CO, which is advantageous in terms of reduction productivity. Low-temperature treatment in an environment containing hydrogen can reduce impurities in the powder while maintaining the nanocrystalline grain size and supersaturated solid solution.

[0043] The reduction process of metal powders can be used in many unrelated applications and industrial processes. Thus, the amount of nano-phase separated powders reduced in a hydrogen-containing atmosphere can be easily scaled up from laboratory scale (on the order of a few grams) to industrial scale (several kilograms), allowing for the scalability and applicability of the process at the industrial scale.

[0044] In commercial applications, ball-milled nano-phase separated powders allow rapid densification to full density at relatively low process temperatures without the application of external pressure during the sintering process, making them suitable for large components with complex shapes manufactured by additive manufacturing processes. The reduction process of loose powders in an atmosphere containing hydrogen, carried out on an industrial scale just before the sintering process, can improve both the process and the final integrity of the printed components. This can be achieved by reducing potential escape gas species and lowering the proportion of remaining oxidized compounds, thereby accelerating the sintering process of nano-phase separated powders and thus reducing the input of resources. The reduction of nano-phase separated powders in a hydrogen-containing atmosphere as an intermediate step after ball milling of the powder and before sintering can be easily integrated into the industrial processing route of additive manufacturing. The degree of hydrogen in the atmosphere can be varied, allowing the reduction temperature to be lowered and the nanocrystalline grain size of the nano-phase separated powder to be preserved.

[0045] Ternary Ni alloys show excellent rapid densification behavior up to high densities around 1100 °C, which is lower than conventional sintering methods for nickel-based alloys, including activated sintering and liquid phase sintering. Acceleration of the sintering process saves resources in terms of temperature and time, which benefits productivity. Densification of these alloys does not require high temperature treatment or isothermal annealing, which reduces the energy input required for full powder consolidation. Faster sintering is also beneficial for higher throughput and general efficiency of the process. The sintering process does not require the application of additional pressure, which allows scalability of part thickness and allows for more complex geometries.

[0046] Ternary Ni alloys can withstand high homologous temperatures while densifying metal powders. Some methods of densifying quickly produce secondary low-melting phases, thus preventing the use of the alloys at high homologous temperatures. In nanophase-segregated Ni alloys, the precipitation of Cu-rich phases at low temperatures does not prevent the use of these alloys at high temperatures, because the alloys are designed such that the secondary phases remelt at high temperatures. Thus, the melting temperature of the entire product remains relatively high.

[0047] Hydrogen low-temperature annealing treatment reduces a very high percentage of interstitial impurities such as oxygen or carbon, which may result from powder contamination or the addition of high-energy ball milling processing aids. Reduction treatment of loose powders before sintering can reduce undesirable elements from the alloy and improve the overall purity of the alloy by reducing the percentage of undesirable oxide phases, which is often a problem for components manufactured by powder metallurgy route. Rapid densification by nanophase separation requires only solid-state processing, and the shape change of the sintered component remains very small. The shape accuracy of sintered components is one of the major challenges in additive manufacturing techniques, which suffers from gravitational slumping due to the formation of liquid phases during sintering. Nanophase-separated Ni alloys facilitate high specific tolerances of the final part shape.

[0048] The mechanical properties of commercial Ni-based alloys benefit from the precipitation of second phases. In ternary or quaternary nanophase-separated alloys, strengthening effects can be expected from the reduction of the final grain size, solid solution strengthening from the addition of ternary elements, and the presence of second phases.

[0049] All the production steps of ternary nanophase separated Ni powders are industrially scalable. Mechanical alloying by ball milling is a commonly used industrial technique, allowing the transition from laboratory (gram scale) to industrial (kilogram or ton scale) powder quantities. Low temperature reduction treatment in hydrogen containing atmospheres is also scalable, depending mainly on the furnace scale and the degree of gas circulation. Ternary and quaternary Ni alloys are the only Ni alloys that benefit from densification by nanophase separated sintering.

[0050] Derivation of gas evolution rate during H2 treatment of ball-milled powders

[0051] Chemical reactions include: TIFF2025506209000002.tif101153 (pre-equilibrium condition: k2 >> k3, k4~0). TIFF2025506209000003.tif99138

[0052] In some circumstances, gas reduction treatments in hydrogen-containing atmospheres can alter the microstructure of ball-milled nanocrystalline powders or initiate nanophase separation processes in Ni alloys, where the gas released to the surface or interior of the powder compact reduces the degree of consolidation or retards densification, at the expense of final density / properties or required resource input.

[0053] As an alternative to degassing, there is a series of alloying components that can be added to act as oxygen getters and enable nanophase-segregated sintering. Alloying elements as selective oxygen getters are characterized by a strong tendency to interact with powder contamination and ball milling process additives to form oxides that retain thermodynamic stability beyond the sintering process window. Thermodynamic stability is characterized by a strong negative heat of formation between the oxygen-getting element and oxygen. The formation of strong oxide compounds promotes nanophase separation at low temperatures without competing powder densification and degassing.

[0054] Oxygen getter elements for ball-milled nanophase-separated sintered Ni alloys are described. Nanophase-separated Ni powders are characterized by an accelerated onset of densification due to the precipitation of second phases at interparticle necks that allow maximum density to be reached at low temperatures. At a certain sintering temperature, fugitive gas species are formed for alloys with all oxides that are unstable in the presence of carbon. By adding elements with stability above the maximum process temperature, nanophase separation can be achieved without hindering the swelling of the microstructure due to gas generation. These getter elements are characterized by a strong preference to form oxide compounds, which is indicated by a high negative heat of formation between the getter and oxygen in the Richardson-Ellingham diagram. Elements that commonly act as oxygen getters for nanophase-separated Ni alloys are: Zr, Cr, V, Mn, or combinations thereof.

[0055] The addition of elements that form stable compounds (at high temperatures) with oxygen can open the processing window of Ni powder alloys that are prone to reduction during sintering, allowing the production of Ni alloy components by additive manufacturing methods. This concept applies very well to Ni alloys designed to promote densification at low temperatures through nanophase separation. These powders can be processed by high energy ball milling with appropriate processing additives in preparation for sintering. Getter elements can be added to alloys that are particularly prone to forming gaseous CO2, CO, and H2O that cannot be removed by annealing treatments before nanophase separation begins.

[0056] The application of oxygen gettering can prevent the interaction between outgassing and densification in nanophase-segregated Ni alloys, which can result in a dense final microstructure with fewer trapped gas pores. Thus, the overall mechanical properties are improved, while the processing time is shortened and the need for energy resources (time, temperature) is reduced. Blends of alloying elements that form stable compounds with oxygen at high temperatures can improve certain mechanical properties, such as strength and hardness, through oxide dispersion strengthening.

[0057] A method of reducing outgassing during sintering of a metal alloy powder may include providing a mechanically alloyed metal alloy powder, annealing the metal alloy powder at an annealing temperature below the sintering temperature, wherein annealing of the metal alloy powder is performed in an atmosphere comprising hydrogen or wherein the metal alloy powder comprises an oxygen getter, or both, and sintering the metal alloy powder at the sintering temperature to reduce outgassing during sintering.

[0058] The hydrogen can be pure hydrogen or hydrogen mixed with an inert gas, for example argon or helium.

[0059] In certain circumstances, the metal alloy powder may be a mechanically alloyed powder. The mechanical alloying (e.g., ball milling) may be performed at a relatively low temperature. For example, in some embodiments, the mechanical alloying (e.g., ball milling) may be performed at a temperature of 150° C. or less, 100° C. or less, 75° C. or less, 50° C. or less, 50° C. or less, while the particles are at a temperature of 150° C. or less, 100° C. or less, 75° C. or less, 50° C. or less, 40° C. or less, 35° C. or less, 30° C. or less, 25° C. or less, or 20° C. or less. In some embodiments, the mechanical processing (e.g., ball milling) may be performed while the particles are at a temperature of at least 0° C. In some embodiments, the mechanical alloying (e.g., ball milling) may be performed at the temperature of the surrounding ambient environment.

[0060] In certain embodiments, the mechanical alloying (e.g., ball milling) may be carried out for a period of 6 hours or more (e.g., 8 hours or more, 10 hours or more, 12 hours or more, or 15 hours or more). In certain embodiments, the mechanical alloying (e.g., ball milling) may be carried out for a period of 18 hours or less. In some embodiments, the mechanical alloying (e.g., ball milling) may be carried out for a period of between 6 hours and 18 hours.

[0061] In certain circumstances, the metal alloy powder may be a nano-phase separated powder.

[0062] In certain circumstances, the metal alloy powder may include additives, such as organic materials. The additives may be impurities in the metal alloy powder. In certain embodiments, the additives may be introduced into the powder during a processing step as a lubricant or other processing aid. The additive may be, for example, an alcohol, such as ethanol.

[0063] In certain circumstances, the metal alloy powder may include nickel, chromium, iron, copper, vanadium, molybdenum, tungsten, silver, zirconium, or combinations thereof. In certain circumstances, the oxygen getter may include an alloying element that has a high tendency to form oxides. Examples of oxygen getters may include zirconium, chromium, vanadium, manganese, or combinations thereof. In certain circumstances, the metal alloy powder may include a binary nano-phase separated powder, a ternary nano-phase separated powder, or a quaternary nano-phase separated powder.

[0064] The alloys described herein include Ni-Cu, Ni-Fe, Ni-Ag, Mo-Cr, Mo-W-Cr, Ni-Cu-Fe, Ni-Cu-Co, Ni-Cu-Cr, Ni-Cu-V, Ni-Cu-Ag, Ni- Cu-Mo, Ni-Cu-W, Ni-Cu-Mn, Ni-Cu-Zr, Ni-Cu-Fe-Mn, Ni-Cu-Co-Mn, Ni-Cu-Cr-Mn, Ni-Cu-V-Mn, Ni-Cu-Ag-Mn, Ni- Cu-Mo-Mn, Ni-Cu-W-Mn, Ni-Cu-Fe-Zr, Ni-Cu-Co-Zr, Ni-Cu-Cr-Zr, Ni-Cu-V-Zr, Ni-Cu-Ag-Zr, Ni-Cu-Mo-Zr, Ni - Can be an alloy that can be at least one of Cu-W-Zr, Ni-Ag-Mn, Ni-Ag-V, Ni-Ag-Cr, Ni-Ag-W, Ni-Ag-Mo, Ni-Ag-Fe, or Ni-Ag-Zr.

[0065] In certain circumstances, the oxygen getter concentration can be about 1 atomic %, about 2 atomic %, about 3 atomic %, about 4 atomic %, or about 5 atomic % of the alloy.

[0066] In certain circumstances, sintering can include nano-phase separation sintering.

[0067] In certain circumstances, the grain size of the metal alloy powder and the grain size of the sintered powder are substantially the same. In certain circumstances, the grain size can be nanoscale features or nanophase. The nanoscale features or nanophase can be 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm or less. Nanophase, nanoscale features, or nanocrystals can refer to crystals (or "particles") having a size of about 1000 nm or less, such as 500 nm, 200 nm, 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, etc. For example, the particle size can be between 1000 nm and about 2 nm, e.g., about 500 nm to about 2 nm, about 200 nm to about 2 nm, about 100 nm to about 2 nm, about 50 nm to about 2 nm, about 30 nm to about 2 nm, about 20 nm to about 2 nm, about 10 nm to about 2 nm. In some embodiments, size can refer to the largest dimension of the particle. Particle size referred to herein can be determined as an "average" and can be measured by any suitable technique. Dimensions can refer to diameter, length, width, height, depending on the shape of the particle. In some instances (and as illustrated below), stable nanocrystalline materials can also refer to materials that include an amorphous phase.

[0068] In another aspect, the metal alloy powder upon sintering can include a mechanically alloyed powder having a reduced amount of gas-evolving species compared to the amount of gas-evolving species in the mechanically alloyed powder prior to annealing in a hydrogen atmosphere.

[0069] In another aspect, a method of forming a sintered alloy can include annealing a nano-phase separated metal alloy powder in the presence of hydrogen and sintering the nano-phase separated metal alloy powder to form a sintered alloy article comprising nickel and having a relative density of at least 80%. The annealing and sintering can be performed in a single step or in successive steps.

[0070] In certain circumstances, the sintered alloy article may include a dispersed oxide, which may be an oxide of an oxygen getter, such as zirconium, chromium, vanadium, manganese, or a combination thereof.

[0071] The dispersed oxide can be the dispersed phase of nanoparticles. The nanoparticles can have a size of about 1000 nm or less, e.g., 500 nm, 200 nm, 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, or 1 nm.

[0072] In certain circumstances, the metal alloy powder can be engineered to have a phase separation temperature at which diffusion of a third metal occurs to phase separate as a nanoscale phase, and preferably the nanoscale phase can re-melt at a transition temperature higher than the phase separation temperature.

[0073] According to certain embodiments, the mechanical alloying (e.g., ball milling) is performed at a relatively low temperature. For example, in some embodiments, the mechanical alloying (e.g., ball milling) is performed at a temperature of 150° C. or less, 100° C. or less, 75° C. or less, 50° C. or less, 50° C. or less, the ball milling) is performed while the particles are at a temperature of 150° C. or less, 100° C. or less, 75° C. or less, 50° C. or less, 40° C. or less, 35° C. or less, 30° C. or less, 25° C. or less, or 20° C. or less. In some embodiments, the mechanical processing (e.g., ball milling) is performed while the particles are at a temperature of at least 0° C. In some embodiments, the mechanical alloying (e.g., ball milling) can be performed at the temperature of the surrounding ambient environment.

[0074] In certain embodiments, the mechanical alloying (e.g., ball milling) can be carried out for a period of 6 hours or more (e.g., 8 hours or more, 10 hours or more, 12 hours or more, or 15 hours or more). In certain embodiments, the mechanical alloying (e.g., ball milling) can be carried out for a period of 18 hours or less. In some embodiments, the mechanical alloying (e.g., ball milling) can be carried out for a period of between 6 hours and 18 hours.

[0075] In some embodiments, the mechanical alloying (eg, ball milling) may be carried out in an inert atmosphere, such as an argon atmosphere.

[0076] In certain circumstances, nanoscale features or nanophases can be 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm, or less. Nanophases, nanoscale features, or nanocrystals can refer to crystals (or "particles") having a size of about 1000 nm or less, such as 500 nm, 200 nm, 100 nm, 50 nm, 20 nm, 10 nm, 5 nm, 2 nm, etc. For example, particle sizes can be between 1000 nm and about 2 nm, such as about 500 nm to about 2 nm, about 200 nm to about 2 nm, about 100 nm to about 2 nm, about 50 nm to about 2 nm, about 30 nm to about 2 nm, about 20 nm to about 2 nm, about 10 nm to about 2 nm. In some embodiments, size can refer to the largest dimension of the particle. Particle sizes referred to herein may be determined as "average" and may be measured by any suitable technique. Dimensions may refer to diameter, length, width, height, depending on the shape of the particle. In some instances (and as shown below), stable nanocrystalline materials may also refer to materials that include an amorphous phase.

[0077] An alloy may be composed of three, four, or more metals. Each metal may have a concentration of about 25 atomic % to about 95 atomic % of the alloy. When two metal components of a ternary alloy each have a concentration of about 25 atomic % to about 95 atomic % of the alloy, the third metal component may have a concentration of about 5 atomic % to about 50 atomic % of the alloy. For example, each metal concentration may be at least 5 atomic %, at least 10 atomic %, at least 15 atomic %, at least 20 atomic %, at least 25 atomic %, at least 30 atomic %, at least 35 atomic %, at least 40 atomic %, at least 45 atomic %, at least 50 atomic %, at least 55 atomic %, at least 60 atomic %, at least 65 atomic %, at least 70 atomic %, at least 75 atomic %, at least 80 atomic %, at least 85 atomic %, at least 90 atomic %, or at least 95 atomic %.

[0078] In another aspect, a method for nano-phase separation sintering of a powder can include providing a mechanically alloyed powder including a first metallic element and a second metal that form a metal alloy, and a third metal having a miscibility gap with the metal alloy, and sintering the mechanically alloyed powder to form a sintered body.

[0079] In another aspect, the metal alloy powder for sintering can include a mechanically alloyed powder including a first metal element and a second metal that form a metal alloy, and a third metal that has a solubility gap with the metal alloy.

[0080] In certain circumstances, the sintered body achieves a density of at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, or at least 98%. These densities can be achieved at low temperatures without the need for application of pressure during sintering. In certain circumstances, the sintering can include nanophase separation sintering.

[0081] According to certain embodiments, sintering the plurality of particles includes heating the particles to a sintering temperature of 2200° C. or less, 2000° C. or less, 1900° C. or less, 1800° C. or less, 1700° C. or less, 1600° C. or less, 1500° C. or less, 1400° C. or less, 1300° C. or less, 1200° C. or less, 1100° C. or less. 1000° C. or less, 900° C. or less, 850° C. or less, 800° C. or less, or 750° C. or less. According to certain embodiments, sintering the plurality of particles includes heating the particles to a sintering temperature of 750° C. or more, 850° C. or more, 1000° C. or more, 1200° C. or more, 1450° C. or more, or 1600° C. or more. Combinations of these ranges are also possible. For example, in some embodiments, sintering the plurality of particles includes heating the particles to a sintering temperature of 750° C. or more and 2200° C. or less. In some embodiments, the temperature of the sintered material is within these ranges for at least 10%, at least 25%, at least 50%, at least 75%, at least 90%, or at least 99% of the sintering time.

[0082] According to certain embodiments, sintering the plurality of particles includes maintaining the particles within a sintering temperature range for 72 hours or less, 48 ​​hours or less, 24 hours or less, 12 hours or less, 6 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, or 1 hour or less (and / or, in some embodiments, at least 10 minutes, at least 20 minutes, at least 30 minutes, at least 50 minutes, at least 3 hours, or at least 6 hours). Combinations of these ranges are also possible. For example, in some embodiments, sintering the plurality of particles includes heating the particles to a first sintering temperature of 600° C. or more and 1100° C. or less for a sintering time of 6 hours or more and 24 hours or less.

[0083] In certain circumstances, the heating rate may be 2° C. / min, 3° C. / min, 4° C. / min, 5° C. / min, 10° C. / min, 15° C. / min, or 20° C. / min.

[0084] In certain circumstances, the grain size of the metal alloy powder and the grain size of the sintered powder may be substantially the same. The grain size may be on the nanoscale.

[0085] The sintered body may include the powders described herein.

[0086] Referring to FIG. 1A, the generalized requirements for nano-phase separation sintering are illustrated, including phase separation, necking, sintering, and densification. To perform these steps, the properties of the alloy are important. For example, nanocrystallinity can ensure rapid diffusion to the particle surface. Furthermore, supersaturation can form the desired second phase at the necks. Mechanical alloying can facilitate both of these key elements.

[0087] Referring to FIG. 1B, the phase diagram suggests an interplay between concentration, temperature, phase separation, reduced surface energy, and high solubility that leads to the phase-separation enhanced sintering described herein.

[0088] FIG. 1C shows an example of a typical process using Fe.

[0089] Ternary and higher Ni-Cu alloy systems are of particular interest. Requirements for the selection of the ternary element include: The ternary element should have a high positive heat of mixing with copper, which can raise the transition temperature from the solubility gap to the solid-solution phase field. The ternary element should also ideally form a solid solution with Ni, which can promote the interdiffusion required for nanophase separation sintering.

[0090] Figure 2A shows the Ni-Cu phase diagram. Figure 2B shows the behavior of the system. For example, increased mobility leads to decreased supercooling, and increased supercooling leads to decreased mobility.

[0091] For example, a 70 at.% Ni, 15 at.% Cu, 15 at.% Co alloy was investigated. The phase diagram for the system is shown in Figure 3. The alloy was heated at different rates (5, 10, 15 °C / min) to 1000 °C and then cooled at 40 °C / min. Figure 4A shows the densification rate at 10 K / min to 1000 °C and then cooled at 40 K / min. Figure 4B shows the evolution of the relative density.

[0092] Cr alloys were also investigated. Figure 5A shows the Ni-Cr phase diagram. Figure 5B shows the Cu-Cr phase diagram. Other phase diagrams at other Cr concentrations can be seen in Figures 6A-6C. Figure 6A shows the Ni-Cu phase diagram at 5 at. % Cr. Figure 6B shows the Ni-Cu phase diagram at 10 at. % Cr. Figure 6C shows the Ni-Cu phase diagram at 15 at. % Cr.

[0093] Alloys with 60 at.% Ni, 25 at.% Cu and 15 at.% Cr were investigated. The phase diagram for 60 at.% Ni and 15% Cr is shown in Figure 6D. Figure 6E is a table showing the composition of the stable phases at 550°C. Figure 6F shows the temperature dependence of densification at 5°C / min to 1200°C and then cooled at 40°C / min.

[0094] Fe alloys were investigated. Figure 7A shows the Ni-Fe phase diagram. Figure 7B shows the Cu-Fe phase diagram. Other phase diagrams at other Fe concentrations can be seen in Figures 8A-8C. Figure 8A shows the Ni-Cu phase diagram at 5 at. % Fe. Figure 8B shows the Ni-Cu phase diagram at 20 at. % Fe. Figure 8C shows the Ni-Cu phase diagram at 42 at. % Fe.

[0095] FIG. 8D shows the Ni-Cu phase diagram at 42 at.% Fe. FIG. 8E is a table showing the composition of the stable phases at 550° C. One set of experiments was performed with 15 at.% Cu. FIG. 8F shows the temperature dependence of densification at 5° C. / min to 945° C. and then cooling at 40° C. / min. FIG. 8G shows the time course of relative density for heating at 5° C. / min. FIG. 8H shows the temperature dependence of densification at 10° C. / min to 1000° C. and then cooling at 40° C. / min. FIG. 8I shows the time course of relative density for heating at 5° C. / min to a final relative density of 0.5864%. FIG. 8J shows the temperature dependence of densification at 15° C. / min to 1000° C. and then cooling at 40° C. / min. FIG. 8K shows the time course of relative density for heating at 15° C. / min to a final relative density of 0.5477%. Figure 8L shows the temperature dependence of densification at 20°C / min to 1000°C and then cooling at 40°C / min. Figure 8M shows the change in relative density over time at 20°C / min heating to a final relative density of 0.4276%.

[0096] Another set of experiments was performed with 15 at. % Cu. Figure 8N shows the temperature dependence of densification at 5°C / min to 1100°C and then cooling at 40°C / min. Figure 8O shows the relative density versus temperature for heating at 5°C / min. Figure 8P shows the relative density versus time for heating at 5°C / min. Figure 8Q shows the temperature dependence of densification at 10°C / min to 1100°C and then cooling at 40°C / min. Figure 8R shows the relative density versus temperature for heating at 10°C / min. Figure 8S shows the relative density versus time at 15°C / min. Figure 8T shows the temperature dependence of densification at 20°C / min to 1100°C and then cooling at 40°C / min. Figure 8U shows the temperature dependence of densification at 20°C / min to 1100°C and then cooling at 40°C / min. Figure 8V shows the relative density versus time at 20°C / min.

[0097] Co alloys were investigated. Figure 9A shows the Ni-Co phase diagram. Figure 9B shows the Cu-Co phase diagram. Other phase diagrams at other Co concentrations can be seen in Figures 10A-10C. Figure 10A shows the Ni-Cu phase diagram at 5 at. % Co. Figure 10B shows the Ni-Cu phase diagram at 20 at. % Co. Figure 10C shows the Ni-Cu phase diagram at 44 at. % Co.

[0098] 12C shows the Ni-Cu phase diagram at 10 at. % V. FIG. 12C shows the Ni-Cu phase diagram at 13 at. % V. FIG. 12D shows the Ni-Cu phase diagram at 13 at. % V. FIG. 12E shows the stable phase at 1150° C. FIG. 12F shows the temperature dependence of the densification rate at 5° C. / min to 1200° C. and then cooled at 40° C. / min. FIG. 12G shows the temperature dependence of the change in relative density.

[0099] Based on the experiments described herein, Ni self-diffusion influences the limit of densification enhancement.

[0100] FIG. 13 is a chart showing the diffusion rates and temperature ranges of the metals described herein.

[0101] Phase diagram information may vary depending on the data source. Figure 14A is a phase diagram of Fe-Cu with 40 at. % Ni obtained from the Fe database. Figure 14B is a phase diagram of Fe-Cu with 40 at. % Ni obtained from the Ni database. Figure 14C is a phase diagram of Fe-Cu with 40 at. % Ni obtained from the Cu database. Figure 14D is a phase diagram of Fe-Cu with 40 at. % Ni obtained from the High Entropy Alloys Database.

[0102] Other phase diagrams can be constructed: Figure 15 is the Cr-Cu phase diagram at 60 at.% Ni; Figure 16 is the Co-Cu phase diagram at 40 at.% Ni; and Figure 17 is the Cu-V phase diagram at 75 at.% Ni.

[0103] Pretreatment of the alloy in a reducing atmosphere can improve the sintering performance of the alloy. For example, pretreatment in hydrogen gas at 300°C for 24 hours can suppress the swelling. Figures 18A, 18B, and 18C show the densification after hydrogen pretreatment at different heating rates.

[0104] As mentioned above, deoxidizers can be included in the alloy. Figure 19 shows the effect on density of adding 5 at. % and 8 at. % Mn to a Ni-Fe-Cu composition.

[0105] As another example, Figure 20 shows the densification behavior of a 37.5at%Ni-37.5at%Co-20at%Cu-5at%Mn composition heated to 1200°C and with the addition of Mn. The microstructure is shown in the images of Figures 21, 22, 23 and 24.

[0106] The mechanical properties of the sintered bodies described herein were tested. The mechanical test results for 37.5 at. % Ni-37.5 at. % Fe-20 at. % Cu-5 at. % Mn are shown in Figures 25-28.

[0107] 29A-29B, Cr meets the thermodynamic criteria for rapid sintering of W and Mo based alloys. Initial testing has demonstrated that sintering is accelerated in Mo and W systems alloyed with Cr, such as W15Cr and Mo15Cr, as shown in Figure 30. Initial testing of Mo25W15Cr samples on sintering has shown relative densities of over 98% for samples heated to 1450°C, as shown in Figure 31.

[0108] In another example, Ag / Zr 16 / 1, 16 / 4, 20 / 4, and 24 / 4 powders were characterized by SEM and XRD with particle size distributions of 1-20 microns, average particle sizes of 6-8 microns, and aspect ratios of 1.5. A second phase of Ag was present with increasing content at the solubility limit. For these powders, sintering in a reducing atmosphere (containing 3% H2) versus pure Ar was important to suppress oxidation and promote sintering and densification, as shown in Figure 32 for 16 at.% Ni, 4 at.% Ag, and Zr.

[0109] The binary Ni-Ag (Ni-20Ag) system exhibits two swelling phenomena at a heating rate of 3°C / min, as shown in Figure 33A. The Ni-Ag powder heat treated at 300°C shows a significant improvement in swelling. Ni-20Ag can have a density up to 91% when heat treated before sintering. See Figure 33B.

[0110] As another example, Figure 34 shows the addition of a getter (in this case Zr) to a Ni-Ag alloy. The addition of Zr to the Ni-Ag alloy system almost eliminates the secondary swelling phenomenon and dramatically reduces the primary swelling phenomenon. APT performed on 16 / 4 Ag / Zr shows that 99.5% of the Zr is present in ZrO clusters distributed throughout the grains and grain boundaries. Zr acts as a getter in the system, and stray oxygen from the PCA is captured in the more stable ZrO instead of forming CO. The lack of grain boundary segregation means that the grains are not necessarily stabilized in the NC regions. The presence of remaining O suggests the need to reduce contaminants or increase Zr or other "getter" elements in the system. Processing parameters such as heating rate (3-50 K / min) and compaction pressure (100-1250 MPa) appear to have little impact on the getter performance. See Figure 35.

[0111] Experimental Method

[0112] In this experiment, we focus on the sintering of a model nanocrystalline material, produced by a relatively standard route, with standard inputs, in order to highlight the physics of the kinetic competition outlined above. Ni was chosen for its technological relevance and because it occupies a unique position: in microcrystalline materials debinding readily precedes sintering, whereas in nanocrystalline materials the onset of sintering is at the low end of the debinding range, so that conflation of organic burnout and sintering is expected to be almost inevitable.

[0113] Nanocrystalline Ni-Fe alloy powders were produced by high-energy ball milling. Nickel powder (Alfa Aesar, 99.9% purity, 3–7 μm particle size) was milled in a SPEX 8000D mixer / mill with a ball-to-powder ratio of 10:1 (5 g powder batches) using hardened steel vials and media. High-energy ball milling was performed in a glove box maintained under an ultra-high purity Ar atmosphere to reduce atmospheric oxygen contamination. Approximately 5 weight percent (wt%) of ethanol (C2H6O) was added as a process control agent (PCA) to balance the fracturing and cold-welding of powder particles during high-energy ball milling. Note that this was the only organic species used in this study and therefore the main carbon source in the system.

[0114] After milling for 20 hours, the powder was imaged in secondary electron (SE) mode with a Merlin Zeiss high-resolution scanning electron microscope (HR-SEM) and the milled powder size was estimated to be 51 (±23) μm. The milled grain size was determined to be about 23 nm using a Panalytical X'Pert PRO with Cu-Kα radiation at 45 kV and 40 mA with a wavelength of λ = 1.5418 Å and step size of 0.0167°. The average grain size was determined from peak broadening corrected for lattice distortion using classical Williamson-Hall analysis and instrumental contributions referenced to NIST LaB6. Although pure Ni is input in this process, wear of the steel media / vials under these milling conditions leads to the formation of Ni-Fe solid solution alloy powder. The final composition of the powder was measured using the energy dispersive X-ray (EDX) spectroscopy detector of the SEM under the same conditions as above. The accumulation of Fe contamination as a function of ball milling time. All powders described herein were produced under the same 20-hour milling conditions and contained an iron content of 9.75 atomic percent (at%) (±0.41), which was generally confirmed by wavelength-dispersive spectroscopy measurements. Wavelength-dispersive spectroscopy (WDS) analysis was based on four separate measurements, all of which were comparable. The analysis was performed on a JEOL JSM7900F scanning electron microscope equipped with an Oxford Wave WDS spectrometer (voltage 20 kV, probe current 1.25 nA). For each element analyzed, Kα radiation was used as the standard references for all elements that were expected to become part of the alloy due to wear of the initial Ni powder with the milling media. The pressed compacts experiments reported below include powders from three independent but otherwise identical ball milling batches. X-ray diffraction confirmed that the milled powders were FCC solid solutions.

[0115] The ball-milled powder was pressed into cylindrical specimens with a diameter and height of about 6 mm and 1.5 mm, respectively, using a uniaxial hydraulic press (Model YLJ-15L, MTI) with a pressure of -400 to 450 MPa acting on the pellets, so that the initial relative density was in the range of -55.8 to 58.9%, and without the addition of any additional binder phase. The initial relative density of the pressed specimens was calculated based on the mass and dimensional measurements, and was calculated as the initial density plus the theoretical density (8.80 g / cm3, taking into account the Fe content). 3 ) The TMA data were expressed as raw change in length converted to relative density, assuming isotropic shape change, which was typically confirmed by caliper measurements after each experiment.

[0116] The details of one or more embodiments are set forth in the accompanying drawings and specification. Other features, objects, and advantages will become apparent from the specification, drawings, and claims. Although a number of embodiments of the invention have been described, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. It will also be understood that the accompanying drawings are not necessarily to scale and that they depict various features and underlying principles of the invention in a somewhat simplified manner.

Claims

1. 1. A method for reducing gas evolution during sintering of a metal alloy powder, comprising: providing a mechanically alloyed metal alloy powder; annealing the metal alloy powder at an annealing temperature below the sintering temperature, wherein the annealing of the metal alloy powder is performed in an atmosphere comprising hydrogen, or the metal alloy powder comprises an oxygen getter, or both; and sintering the metal alloy powder at a sintering temperature to reduce gas evolution during sintering; A method comprising:

2. The method of claim 1 , further comprising pressing the annealed metal alloy powder to form a compact prior to sintering.

3. The method of claim 1 , further comprising pressing the annealed metal alloy powder to form a compact prior to annealing.

4. The method of claim 1 , wherein the metal alloy powder is a nanophase separated powder.

5. The method of claim 1 , wherein the metal alloy powder comprises an additive.

6. The method of claim 1 , wherein the additive comprises an organic material.

7. The method of claim 1 , wherein the metal alloy powder comprises nickel.

8. The method of claim 1 , wherein the metal alloy powder comprises chromium.

9. The method of claim 1 , wherein the metal alloy powder comprises iron.

10. The method of claim 1 , wherein the metal alloy powder comprises copper.

11. The method of claim 1 , wherein the metal alloy powder comprises vanadium.

12. The method of claim 1 , wherein the metal alloy powder comprises molybdenum.

13. The method of claim 1 , wherein the metal alloy powder comprises tungsten.

14. The method of claim 1 , wherein the metal alloy powder comprises silver.

15. The method of claim 1 , wherein the metal alloy powder comprises zirconium.

16. The method of claim 1 , wherein the metal alloy powder comprises a ternary nanophase separated powder.

17. The method of claim 1 , wherein the oxygen getter comprises an alloying element that has a high tendency to form oxides.

18. 18. The method of claim 17, wherein the oxygen getter comprises zirconium, chromium, vanadium, manganese, or a combination thereof.

19. 19. The method of claim 18, wherein the concentration of the oxygen getter is between about 1 atomic % and about 4 atomic % of the alloy.

20. The method of claim 1, wherein the annealing temperature is between about 200°C and 400°C.

21. The method of claim 1 , wherein the sintering comprises nanophase separation sintering.

22. The method of claim 1 , wherein the particle size of the metal alloy powder and the particle size of the sintered powder are substantially the same.

23. A metal alloy powder for sintering, comprising a mechanically alloyed powder having a reduced amount of gas-generating species compared to the amount of gas-generating species in the mechanically alloyed powder before annealing in a hydrogen atmosphere.

24. 24. The powder of claim 23, wherein the mechanically alloyed powder is a nanophase separated powder.

25. 24. The powder of claim 23, wherein the mechanically alloyed powder further comprises the oxygen getter.

26. 24. The powder of claim 23, wherein the mechanically alloyed powder comprises nickel, chromium, iron, copper, vanadium, molybdenum, tungsten, silver, zirconium, or a combination thereof.

27. 24. The powder of claim 23, wherein the mechanically alloyed powder is a ternary nanophase separated powder or a quaternary nanophase separated powder.

28. A sintered body comprising the powder described in claim 23.

29. 1. A method of forming a sintered alloy, comprising: Annealing the nanophase separated metal alloy powder in the presence of hydrogen; and sintering the nanophase-separated metal alloy powder to form a sintered alloy article comprising nickel and having a relative density of at least 80%; A method comprising:

30. 30. The method of claim 29, wherein the sintered alloy article comprises dispersed oxides.

31. 30. The method of claim 29, wherein the annealing and sintering are performed in a single step.

32. 30. The method of claim 29, wherein the annealing and sintering are performed in successive steps.

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