Mechanically alloyed powder raw material

Abstract

Disclosed herein are embodiments of mechanically alloyed powder feedstocks and methods for spheroidizing the feedstocks using microwave plasma processing. The spheroidized powders can be used in metal injection molding processes, hot isostatic pressing, and additive manufacturing. In some embodiments, mechanical comminution, e.g., ball milling, can be used to prepare high-entropy alloys for microwave plasma processing.

Description

Technical Field

[0001] Incorporation by reference to priority applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 840,607, filed on April 30, 2019, titled "MECH A NICALLY ALLOYED POWDER FEEDSTOCK", the contents of which are hereby incorporated by reference in their entirety.

[0002] Generally, in some embodiments, the present disclosure is directed to manufacturing metallic spherical or elliptical powder products that include properties achieved by mechanical alloying.

Background Art

[0003] Metal powders are industrially used in certain applications. Recently, there has been increasing interest in metal powders for use in additive manufacturing. Metal alloy powders are generally produced by various spraying techniques - water spraying, gas spraying, or thermochemical methods. The morphology of the powders produced can depend on the method of powder production. Further, various morphologies can be suitable for various consolidation methods or uses of the powders. For example, additive manufacturing (AM), particularly laser-based AM systems, such as powder bed fusion, can benefit from spherical powders due to their excellent flowability, spreadability, and packing density.

Summary of the Invention

[0004] Disclosed herein are embodiments of a method for producing spheroidized powder from mechanically alloyed feedstock, the method comprising preparing a mechanically alloyed powder feedstock by mechanically grinding at least five elemental powders to mechanically alloy the at least five elemental powders; and introducing the mechanically alloyed powder feedstock into a microwave plasma torch, a plasma plume of the microwave plasma torch, and / or an exhaust device of the microwave plasma torch; and at least partially melting and spheroidizing the mechanically alloyed powder feedstock within the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch to form a spheroidized powder.

[0005] Also disclosed herein are embodiments of a method for producing spheroidized powder from mechanically alloyed feedstock, the method comprising preparing a mechanically alloyed powder feedstock by mechanically grinding one or more precursors to form a high entropy alloy; and introducing the mechanically alloyed powder feedstock into a microwave plasma torch, a plasma plume of the microwave plasma torch, and / or an exhaust device of the microwave plasma torch; and at least partially melting and spheroidizing the mechanically alloyed powder feedstock within the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch to form a spheroidized powder.

[0006] Furthermore, embodiments of a method for producing spheroidized powder from mechanically alloyed feedstock are disclosed herein, the method including introducing the mechanically alloyed powder feedstock into a microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust of the microwave plasma torch, the mechanically alloyed powder feedstock being produced by mechanically grinding at least five elemental powders to mechanically alloy the at least five elemental powders, and melting and spheroidizing the mechanically alloyed powder feedstock within the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust of the microwave plasma torch to form the spheroidized powder. It is characterized by being prepared by melting and spheroidizing in the exhaust of the microwave plasma torch to form spheroidized powder.

[0007] In some embodiments, the spheroidized powder can be melted and spheroidized for use in a metal injection molding process. In some embodiments, the spheroidized powder can be melted and spheroidized for use in a hot isostatic pressing process. In some embodiments, the spheroidized powder can be melted and spheroidized for use in an additive manufacturing process.

[0008] In some embodiments, the mechanically alloyed powder feedstock can be mechanically ground by ball milling. In some embodiments, melting the mechanically alloyed powder feedstock can be performed in less than 1 second. In some embodiments, melting the mechanically alloyed powder feedstock can be performed in less than 500 milliseconds.

[0009] In some embodiments, the mechanically alloyed powder feedstock may include Ti, Zr, Nb, Ta, Fe. In some embodiments, the mechanically alloyed powder feedstock may include Al, Fe, V, Si. In some embodiments, the mechanically alloyed powder feedstock may include Fe, Co, Ni, Cr, Ti. In some embodiments, the mechanically alloyed powder feedstock may include Fe, Co, Ni, Cr, Al. In some embodiments, the mechanically alloyed powder feedstock may include Fe, Co, Ni, Cr, Cu. In some embodiments, the mechanically alloyed powder feedstock may have a microstructure, and the spheroidized powder maintains the microstructure.

[0010] Spheroidized powder formed from the method of embodiments of the present disclosure.

Brief Description of the Drawings

[0011]

Figure 1

[0012]

Figure 2

[0013]

Figure 3

[0014]

Figure 4

[0015]

Figure 5A

Figure 5B

[0016]

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments of methods, devices, and assemblies for using mechanically alloyed materials (e.g., powders) as raw materials, particularly for microwave plasma processing and powders and products manufactured therefrom, are disclosed herein. Preparing such powders from mechanically alloyed raw materials was extremely difficult, but unexpected properties have been achieved based on the embodiments of this disclosure.

[0018] In some embodiments, a mechanically milled alloy can be created by grinding materials together to form a desired composition of powder particles. Other methods of alloying may be used as well, and the present disclosure is not limited to mechanical milling. In some embodiments, the mechanically milled alloy may be a high entropy alloy (HEA), a complex concentrated alloy (CCA), or a modified alloy from existing alloys. An HEA is an alloy that mainly contains five or more elements in equiatomic or non-equiatomic percentages. The powder, or other components, can then be used as a raw material (e.g., powder raw material) for a microwave plasma process to form a final spheroidized powder, which can then be used in different processes, such as additive manufacturing processes.

[0019] There is a need to develop new alloys, such as high entropy alloys (HEAs), that exhibit excellent properties when processed by additive manufacturing methods.

[0020]

[0021] ​Furthermore, with the advent of additive manufacturing (AM), there is an increasing need to develop new alloys that can be processed by AM and challenge the limits of properties obtained by conventional or existing alloys.

[0022] In some embodiments, a HEA may be an alloy formed by mixing a relatively large number of elements in equivalent or relatively large proportions. In some embodiments, the number of elements in a HEA may be 3 or more, 4 or more, 5 or more, or 6 or more, 7 or more, 8 or more. In some embodiments, the relative proportions by atomic percentage may be equivalent or nearly equivalent. In some embodiments, a HEA may be an alloy having a high mixing entropy of, for example, 1.67R (or greater than about 1.67R), as described in JOM by, for example, Z. Li and D. Raabe, 2017, DOI: 10.1007 / s11837-017-2540-2, which is incorporated herein by reference.

[0023] HEAs can have advantageous properties or combinations of properties compared to conventional alloys being used, such as high elevated temperature strength, high temperature oxidation resistance, high corrosion resistance, and high strength-to-weight ratios. Due to the limited mutual element solubility, most composition HEAs, particularly non-equiatomic HEAs, are difficult or impossible to produce by conventional methods such as arc melting and induction melting. Furthermore, the large differences in melting points of the alloying elements in HEAs limit processing by conventional methods.

[0024] Such elements can be alloyed in the solid state by, for example, mechanical alloying techniques where elemental powders, pre-alloyed powders, or master alloy powders are milled in a ball mill until a homogeneous alloy is formed. In a ball mill, the alloy is obtained by mechanically forcing the combination of the alloy. This alloying can then be homogenized over time. The homogenization of the alloy is often monitored by x-ray diffraction (XRD), where the initial individual element peaks of the alloying elements gradually disappear and new peaks of the alloyed phase(s) appear.

[0025] For example, different processes can occur during alloying depending on appropriate ball mill parameters such as the ball-to-metal ratio, rotation speed, and / or ball size. For example, the resulting powder may have undergone agglomeration, mechanical alloying, mixing, blending, or milling. Some or all of these may occur during such processes.

[0026] However, the resulting powder is in an irregular and flake-like form, limiting further processing / consolidation techniques such as spark plasma sintering. Embodiments of this disclosure relate to the production of spherical HEA powders processed by mechanical alloying and treated by microwave plasma spheroidization. are described. The spherical powders can then be used in the context of industrial powder consolidation processes such as additive manufacturing, metal injection molding, hot isostatic pressing, and powder forging.

[0027] Mechanical alloying is a solid-state powder metallurgy process in which elemental powder particles or pre-alloyed powder particles are milled by a high-energy ball mill. The powder particles are subjected to repeated cold welding, crushing, and re-welding during this process. The transfer of mechanical energy to the powder particles causes strain in the powder by generating dislocations that act as rapid diffusion paths. Figure 6 shows an example of such a method. As shown, elemental powder (left) can be mechanically milled (center) to produce feedstock (right).

[0028] Furthermore, the diffusion distance is reduced due to the refinement of the particles. Therefore, this process can produce alloys with phases and microstructures different from those of the raw material powder. The actual grinding time can vary depending on the feedstock and the alloy. For example, it can be more than 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours (or about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 hours). In some embodiments, the grinding can continue for less than 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 hours (or about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 hours). In some embodiments, the grinding can continue until partial or complete homogenization is achieved, for example, by monitoring the XRD pattern and tracking the disappearance of the peaks of the individual elements.

[0029] Advantageously, mechanical alloying can increase the homogenization of the particles because the elements are mechanically forced together, reducing the diffusion paths between the alloying elements. This homogenization can also be improved by increasing the grinding time.

[0030] Microwave-assisted plasma technology can reach temperatures of up to about 6000 K and provide a continuous and sustainable plasma plume. By adjusting the characteristics of the plasma plume, such as the plume length and plume density, it is possible to spheroidize or homogenize mechanically alloyed, highly irregular or flaky HEAs or mechanically alloyed powders. Furthermore, by adjusting the location where the raw material enters the plasma plume, the plasma afterglow, or the plasma exhaust device of the microwave plasma torch, the temperature to which the raw material is subjected can be adjusted.

[0031] Irregular or flaky powders may limit the processing method to spark plasma sintering, so it may be advantageous to spheroidize such powders for more extended use across powder consolidation methods. For example, for HIP to achieve full density after HIP, it is beneficial for the tap density of the powder to be greater than about 60% of the theoretical density of the alloy. For other powder processing methods, for example, during additive manufacturing, it is beneficial to have high powder fluidity and / or spreadability. Irregular and flaky powders have poor flow characteristics, making it difficult or impossible to process them. Therefore, microwave plasma processing can convert irregular and flaky powders into spherical powders that can be used in various manufacturing processes.

[0032] Due to the short residence time in the microwave plasma process, which is estimated to be at most a few hundred milliseconds at high temperatures, the powder is partially melted, promoting the homogenization of the mechanically alloyed powder.

[0033] Accelerating the processing of mechanically alloyed particles through microwave plasma processing by heat increases the diffusion of alloying elements into the bulk of the particles, thereby increasing homogeneity. After plasma processing, the spherical HEA powder can then be processed by various industrial powder consolidation methods, such as but not limited to, additive manufacturing (AM), metal injection molding (MIM), powder forging, and hot isostatic pressing (HIP), subjecting the HEA to mainstream industrial processing.

[0034] The raw material is produced from mechanical alloying and then contains a specific material composition. The process parameter set for microwave plasma processing may be selected based on the material composition. The process parameters may be adjusted to allow for variations in homogeneous alloying and / or spheroidization.

[0035] This set of process parameters may include microwave power, plasma gas flow, gas type, plasma plume length, plasma plume diameter, plasma jet speed, exhaust chamber pressure, quench gas, exhaust gas speed, feedstock speed relative to the plasma jet speed, supply gas flow rate, and feedstock supply speed, or combinations thereof. This set of process parameters may further include portions of the plasma, plasma plume, and / or plasma exhaust device into which the feedstock enters. For example, the feedstock may be supplied to a cooler region of the plasma exhaust device when a lower temperature is desired.

[0036] As disclosed herein, melting may include completely melting, partially melting, or melting the surface of the particulate feedstock.

[0037] Feedstock Feedstocks for microwave plasma processing can be developed by mechanical alloying. Advantageously, in mechanical alloying, alloys that are difficult or impossible to produce by other alloying methods, such as arc melting and induction melting, can be developed. The unique alloys that can be formed by mechanical alloying include HEAs whose unique properties relative to conventional alloys have been demonstrated at the laboratory scale.

[0038] In mechanical alloying, the feedstock can be mechanically milled to achieve homogenization, which can be measured / monitored using XRD techniques. As the time for mechanical alloying increases, different peaks appear in the XRD spectrum, suggesting the formation of alloyed phases. Milling is continued until a stable XRD spectrum is obtained, which is a spectrum that does not change with increasing milling time, thereby suggesting a chemically stable alloy.

[0039] The resulting powder is highly irregular and flaky due to intensive mechanical milling. For example, the irregular powder can be particles having an irregular or circular shape, such as powder sprayed in water. On the other hand, the flaky powder can have a relatively large aspect ratio, and is thin, with a very low apparent density and packing density, which makes it difficult to flow, spread, and process the powder. Both the irregular powder and the flaky powder are not suitable for industrial powder consolidation methods.

[0040] However, it has been demonstrated that the powder obtained from mechanical milling is an ideal raw material for microwave plasma processing. Microwave plasma processing can spheroidize the machined powder in an irregular or flaky form. Figure 1 shows the time-dependent evolution of an exemplary raw material powder during the milling process. XRD scans performed on powders mechanically milled for 1 hour, 4 hours, 8 hours, and 17 hours are shown. As shown, as time increases, some peaks in the XRD scans attenuate or substantially disappear. Further, new peaks become higher or appear, which suggests the formation or increase of alloyed phases.

[0041] Due to their exceptional properties, HEAs are interesting for several applications. For example, medical The TiZrNbTaFe HEA for implants shows significantly improved corrosion resistance compared to the currently used Ti-6Al-4V alloy. The AlFeVSi alloy has high strength and high thermal stability and can be interesting for the aircraft industry due to potential structural weight reduction. Similarly, the FeCoNiCrTi or FeCoNiCrAl HEA has been shown to achieve exceptional tensile properties at room temperature and is attractive for many industrial applications. In some embodiments, the FeCoCrNiCu HEA can be used.

[0042] Mechanically alloyed powders, when spheroidized by microwave plasma processing, result in highly spherical powders. This spherical powder can then be used as a raw material for various industrial consolidation methods such as additive manufacturing, metal injection molding, powder forging, and hot isostatic pressing. Advantageously, the microstructure (or nanostructure) of the mechanically milled powder can be maintained through processing, for example, after plasma processing.

[0043] Figure 2 shows 、 ma XRD spectra of an example powder having a composition as an example including 25Fe-17Co-17Cr-17Ni-16Cu before and after microwave plasma processing spheroidization. Other example compositions include Fe-25, Ni-19, Cr-13, Co-0.45, Ti-2.5, Mo-2.4, Nb-.4, Cu-0.2, Re. Line 202 shows the XRD plot of the powder raw material 17 hours after mechanical alloying but before microwave plasma processing. Line 204 shows the XRD plot of the powder raw material after microwave plasma processing.

[0044] As shown, the alloy becomes more homogenized after the spheroidization process. Homogenization refers to forming the alloy from the starting individual elemental powders. This can be seen from the XRD spectra where the individual peaks representing the elements disappear and alloy peaks appear. After spheroidization, the alloy peaks become clearer and the remaining background peaks are removed, suggesting an improvement in the homogenization of the mechanically alloyed powder. Thus, microwave plasma processing not only spheroidizes the powder raw material but also further homogenizes the raw material.

[0045] With appropriate optimization, the grinding time for mechanical alloying can be reduced because homogenization can be achieved using microwave plasma processing spheroidization. Although not limited by a single theory, mechanical alloying significantly reduces the diffusion distance within the powder because grinding produces purified grains. Therefore, after mechanical alloying, during microwave plasma processing, diffusion occurs rapidly at high temperatures, which can improve the homogenization of the alloy produced by mechanical alloying. Therefore, microwave plasma processing can create similar homogenization for longer periods of the grinding time for mechanical alloying. The grinding time may be shortened when the raw material is microwave plasma processed.

[0046] Mechanical alloying can also be used for alloys other than HEAs. By mechanical alloying, any existing alloy, such as stainless steel, such as stainless steel types 316 and 17-4, or Ni-based Inconel, such as 718, 625, 738, etc., can also be manufactured. Embodiments of the present disclosure can be used effectively and economically to develop new alloys or to modify existing alloys used in new consolidation techniques, such as additive manufacturing.

[0047] Mechanical alloying is a solid process. Therefore, technically, any alloy can be produced by mechanical alloying. However, for conventional alloys or alloys that can be produced in a liquid state such as melting, these processes are much faster and more economical than mechanical alloying. Therefore, they are rarely used for such alloys. Nevertheless, mechanical alloying is also used to produce alloys that can be produced in a liquid state, such as by melting. obtained.

[0048] Spheroidization In some embodiments, the final particles achieved by plasma processing can be spherical or ellipsoidal, and these terms can be used interchangeably. Advantageously, by using the important and specific disclosures associated with each of the various raw materials disclosed, all of the raw materials can be converted into spherical powders.

[0049] Embodiments of the present disclosure are directed to generating particles that are substantially spherical or ellipsoidal or have undergone significant spheroidization. In some embodiments, spherical, spheroidal or spheroidized particles refer to particles having a sphericity exceeding a certain threshold. Sphericity is calculated using the following formula with the volume V that matches the volume of the particle to calculate the surface area of sphere A s, ideal :

Number

Number

[0050] In some embodiments, the particles can have a sphericity greater than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or greater than about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, the particles can have a sphericity of 0.75 or greater or 0.91 or greater (or about 0.75 or greater or about 0.91 or greater). In some embodiments, the particles can have a sphericity less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or less than about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, the particles are considered spherical, spheroidal or spheroidized when they have a sphericity that is any of or exceeds the above sphericity values, and in some preferred embodiments, the particles are considered spherical when their sphericity is about 0.75 or greater, or about 0.91 or greater.

[0051] In some embodiments, the median sphericity of all particles in a given powder can be greater than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or greater than about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, the median sphericity of all particles in a given powder can be less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, a powder is considered spheroidized when all or a threshold percentage of the particles (as described by any of the following fractions) for a given powder have a median sphericity greater than or equal to any of the above sphericity values. In some preferred embodiments, a powder is considered spheroidized when all or a threshold percentage of the particles have a median sphericity of about 0.75 or greater, or about 0.91 or greater.

[0052] In some embodiments, for example, the fraction of particles in a powder that can exceed a given sphericity threshold, as described above, can be greater than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or greater than about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 99%). In some embodiments, for example, the fraction of particles in a powder that can exceed a given sphericity threshold, as described above, can be less than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or less than about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 99%).

[0053] The particle size distribution and sphericity can be determined by any suitable known technique, for example, SEM, optical microscopy, dynamic light scattering, laser diffraction, manual measurement of dimensions using image analysis software with, for example, about 15 - 30 measurements per image over at least three images of a cross-section or sample of the same material, and any other technique.

[0054] Microwave plasma processing The process parameters can be optimized to obtain maximum spheroidization depending on the initial state of the powder. For each raw material powder characteristic, the process parameters can be optimized for a specific result. U.S. Patent Application Publication No. 2018 / 0297122, U.S. Patent No. 8,748,785, and U.S. Patent No. 9,932,673 disclose certain processing techniques that can be specifically used in the disclosed processes, specifically microwave plasma processing. Accordingly, U.S. Patent Application Publication No. 2018 / 0297122, U.S. Patent No. 8,748,785, and U.S. Patent No. 9,932,673 are hereby incorporated by reference in their entirety, and the technology should be considered applicable to the raw materials described herein.

[0055] One aspect of the present disclosure includes a process for spheroidizing metals and metal alloys using microwave-generated plasma. The powder feedstock is introduced into an inert and / or reducing and / or oxidizing gas environment and injected into a microwave plasma environment. Upon injection into the high-temperature plasma, the feedstock is spheroidized and discharged into a chamber filled with an inert gas and directed to a sealed drum in which the material is stored. This process can be carried out at atmospheric pressure, in a partial vacuum, or at a pressure slightly above atmospheric pressure. In alternative embodiments, the process can be carried out in a low, medium, or high vacuum environment. The process can be carried out continuously, and the drum is replaced when filled with spheroidized metal or metal alloy particles.

[0056] The rate of cooling of the spheroidized metals and metal alloys can be controlled to strategically affect the microstructure of the powder. By controlling process parameters such as cooling gas flow rate, residence time, cooling gas composition, etc., the microstructure of the metals and metal alloys can be controlled. The exact cooling rate required to form these structures depends primarily on the type and amount of alloying elements within the material.

[0057] The rate of cooling, especially when combined with the consistent and uniform heating ability of the microwave plasma plume, enables control over the final microstructure. As a result, the above method can be applied to the processing of metal (e.g., mechanically alloyed and / or HEA) raw materials. It can be applied to the processing of metal (e.g., mechanically alloyed and / or HEA) raw materials.

[0058] Cooling treatment parameters include, but are not limited to, cooling gas flow rate, residence time of the spheroidized particles in the hot zone, and composition or manufacturing method of the cooling gas. For example, the cooling rate or quenching rate of the particles can be increased by increasing the flow rate of the cooling gas. The faster the cooling gas flows beyond the spheroidized particles exiting the plasma, the faster the quenching rate - which enables the confinement of a certain desired microstructure. The residence time of the particles within the hot zone of the plasma can also be adjusted to impart control over the resulting microstructure. That is, the degree of melting of the particles (i.e., the extent to which the particle surface is melted compared to the innermost part or core of the particle) is determined by the length of time the particles are exposed to the plasma.

[0059] As a result, the degree of melting affects the degree of cooling required for solidification and is thus a cooling process parameter. The change in microstructure can be incorporated throughout the particle or only in part thereof, depending on the degree of melting of the particles. The residence time can be adjusted by adjusting the operating variable values such as the particle injection rate and flow rate (and conditions such as laminar or turbulent flow) within the hot zone. Equipment modifications can also be used to adjust the residence time. For example, the residence time can be adjusted by changing the cross-sectional area of the hot zone.

[0060] Another variable or controllable cooling process parameter is the composition of the cooling gas. Certain cooling gases are more thermally conductive than others. For example, helium is said to be a highly thermally conductive gas. The higher the thermal conductivity of the cooling gas, the faster the spheroidized particles can be cooled / quenched. By controlling the composition of the cooling gas (e.g., controlling the amount or ratio of a high thermal conductivity gas to a low thermal conductivity gas), the cooling rate can be controlled.

[0061] As is known in metallurgy, the microstructure of a metal is determined by the composition of the metal, as well as the heating and cooling / quenching of the material. In the present technology, by selecting (or knowing) the composition of the raw material, then exposing the raw material to a plasma having a uniform temperature profile and control over what is provided by a microwave plasma torch, and subsequently selecting and controlling the cooling parameters, control over the microstructure of the spheroidized metal particles is achieved. Also, the phase of the metal material depends on the composition of the raw material (e.g., purity, purity of alloying elements, composition, etc.), as well as the thermal processing.

[0062] In one exemplary embodiment, an inert gas continuously purges around the powdered metal feed to remove oxygen in the powder feed hopper. A continuous amount of the powder feed is then taken into the inert gas and fed to a microwave generating plasma for dehydrogenation or for maintaining the composition / purity of the spheroidized particles. In one example, the microwave generating plasma may be generated using the microwave plasma torches described in U.S. Patent Application Publication No. US2013 / 0270261, and / or U.S. Patents Nos. 8,748,785, 9,023,259, 9,206,085, 9,242,224, and 10,477,665, each of which is hereby incorporated by reference in its entirety.

[0063] In some embodiments, the particles are exposed to a uniform temperature profile between 4,000 and 8,000 K within a microwave-generated plasma. In some embodiments, the particles are exposed to a uniform temperature profile between 3,000 and 8,000 K within a microwave-generated plasma. Within the plasma torch, the powder particles are rapidly heated and melted. Liquid convection accelerates H2 diffusion throughout the molten particles, continuously guiding hydrogen (H2) to the surface of the liquid metal hydride leaving the particles and reducing the time required for each particle to be in the process environment compared to the solid process. When the particles are incorporated into an inert gas, for example, argon, generally the contact between particles is minimized, significantly reducing the occurrence of particle agglomeration. The need for post-process sorting is thus significantly reduced or eliminated, and the resulting particle size distribution can be virtually the same as that of the input feed material. In an exemplary embodiment, the particle size distribution of the feed material is maintained in the final product.

[0064] Within the plasma, the molten metal is essentially spheroidized due to liquid surface tension. When the microwave-generated plasma exhibits a substantially uniform temperature profile, spheroidization of more than 90% (e.g., 91%, 93%, 95%, 97%, 99%, 100%) of the particles can be achieved. After exiting the plasma, the particles are cooled before entering the collection flask. The collection flask can be removed and replaced with an empty flask as needed without stopping the process when full.

[0065] Figure 3 is a flowchart showing an exemplary method (250) for generating spherical powder according to an embodiment of the present disclosure. In this embodiment, the process (250) begins by introducing a feed material into a plasma torch (255). In some embodiments, the plasma torch is a microwave-generated plasma torch or an RF plasma torch. Inside the plasma torch, the feed material is exposed to the plasma to melt the material as described above (260). The melted material is spheroidized by surface tension as discussed above (260b). After exiting the plasma, the product cools and solidifies, is trapped in a spherical shape, and is then collected (265).

[0066] In some embodiments, the bottle environment and / or the sealing requirements are carefully controlled. That is, the bottle environment and sealing are tailored to the application to prevent powder contamination and potential oxidation. In one embodiment, the bottle is under vacuum. In one embodiment, the bottle is sealed after being filled with the powder produced by the present technique. In one embodiment, the bottle is also filled with an inert gas, such as argon. Due to the continuous nature of the process, once filled, the bottle can be removed as needed and replaced with an empty bottle without stopping the plasma process.

[0067] The methods and processes according to the present disclosure can be used to produce powders, such as spherical powders.

[0068] In some embodiments, the processing discussed herein, such as microwave plasma processing, can be controlled to prevent and / or minimize the leakage of certain elements from the raw material during melting and can maintain the desired composition / microstructure.

[0069] Figure 4 shows an exemplary microwave plasma torch that can be used for the generation of powders. As discussed above, the feed materials 9, 10 can be introduced into the microwave plasma torch 3 that sustains the microwave-generated plasma 11. In one example embodiment, the intake gas flow and the sheath flow (downward arrows) can be injected through the inlet 5 prior to the ignition of the plasma 11 via the microwave radiation source 1 to create a flow regime within the plasma torch.

[0070] In some embodiments, while both the intake flow and the sheath flow are axisymmetric and laminar, in other embodiments, the gas flow is swirling. The feed material 9 is introduced axially into the microwave plasma torch, where the material is entrained by a gas flow that directs the material towards the plasma. As discussed above, the gas flow can consist of noble gas columns of the periodic table, such as helium, neon, argon, etc. Within the microwave-generated plasma, the feed material is melted to spheroidize the material. The inlet 5 can be used to introduce process gas and entrain and accelerate the particles 9, 10 along the axis 12 towards the plasma 11. First, the particles 9 are accelerated by entrainment using a laminar gas flow (upper set of arrows) created through an annular gap within the plasma torch. A second laminar flow (lower set of arrows) is created through a second annular gap to impart a laminar sheath to the inner wall of the dielectric torch 3 and protect it from melting due to thermal radiation from the plasma 11. In an exemplary embodiment, the laminar flow directs the particles 9, 10 along a path as close as possible to the axis 12 towards the plasma 11, exposing the particles to a substantially uniform temperature within the plasma. In an exemplary embodiment, the laminar flow directs the particles 9, 10 along a path as close as possible to the axis 12 towards the plasma 11, exposing the particles to a substantially uniform temperature within the plasma.

[0071] In some embodiments, a suitable flow state exists to avoid the particles 10 reaching the inner wall of the plasma torch 3 where plasma attachment can occur. The particles 9, 10 are each induced by a gas flow towards the microwave plasma 11 that undergoes a uniform heat treatment. Various parameters of the microwave-generated plasma, as well as particle parameters, may be adjusted to achieve the desired result. These parameters may include microwave power, feedstock size, feedstock insertion rate, gas flow rate, plasma temperature, residence time, and cooling rate. In some embodiments, the cooling or quenching rate is 10 +3 °C / second or more when exiting the plasma 11. As discussed above, in this particular embodiment, the gas flow is laminar; however, in alternative embodiments, a vortex or turbulent flow may be used to direct the feedstock towards the plasma.

[0072] Figures 5A - B show an exemplary microwave plasma torch that enables downstream feeding by including a side feed hopper instead of the top feed hopper shown in the embodiment of Figure 4. Thus, in this embodiment, the raw material is injected after the microwave plasma torch applicator for processing in the "plume" or "exhaust" of the microwave plasma torch. Thus, the plasma of the microwave plasma torch is secured at the exit end of the plasma torch, enabling downstream feeding of the raw material, in contrast to the top (or upstream) feeding discussed with respect to Figure 4. This downstream feeding can advantageously extend the life of the torch because the hot zone is protected from any material deposits on the walls of the hot zone liner. Further, this enables the securing of a suitable temperature downstream of the plasma plume for optimal melting of the powder through accurate targeting of the temperature level and residence time. For example, there is the ability to adjust the length of the plume using microwave powder, the gas flow, and the pressure in the quenching vessel including the plasma plume.

[0073] In general, the downstream spheroidization method can utilize two main hardware configurations to establish a stable plasma plume: an annular torch, as described, for example, in US Patent Application Publication No. 2018 / 0297122, or a vortex torch, as described, for example, in US 8,748,785 B2 and US 9,932,673 B2. Figures 5A and 5B show embodiments of the method that can be performed by either an annular torch or a vortex torch. A feeding system that is tightly coupled with the plasma plume at the exit of the plasma torch is used to feed the powder axially symmetrically to protect the homogeneity of the process.

[0074] Other feed configurations may include one or several individual feed nozzles surrounding the plasma plume. The feed powder may enter the plasma at a point from any direction and may be fed to that point in the plasma from any direction 360° around the plasma. The feed powder may enter the plasma at a specific location along the length of the plasma plume where a specific temperature is measured and with a residence time estimated for sufficient melting of the particles. The molten particles exit the plasma into a sealed chamber where they are quenched and then collected.

[0075] The feed material 314 may be introduced into the microwave plasma torch 302. The hopper 306 provides the feed material 314 to the microwave plasma torch 302, the plume, or an exhaust system. It may be used to store the feed material 314 before feeding. The feed material 314 may be injected at any angle, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 degrees, to the longitudinal direction of the plasma torch 302. In some embodiments, the feed material may be injected at an angle greater than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 degrees. In some embodiments, the feed material may be injected at an angle less than 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or 55 degrees. In alternative embodiments, the feed material may be injected along the longitudinal axis of the plasma torch.

[0076] Microwave radiation can be directed to the plasma torch through waveguide 304. Feedstock 314 is supplied to plasma chamber 310 and is disposed in contact with the plasma generated by plasma torch 302. The feedstock melts when it contacts the plasma, plasma plume, or plasma exhaust. Feedstock 314 remains in plasma chamber 310 but cools and solidifies before being collected in container 312. Alternatively, feedstock 314 can exit plasma chamber 310 but still be in a molten phase and cools and solidifies outside the plasma chamber. In some embodiments, a quenching chamber, which may or may not use positive pressure, may be used. Although described separately from FIG. 4, it is understood that the embodiments of FIGS. 5A - 5B use similar features and conditions as the embodiment of FIG. 4.

[0077] In some embodiments, the implementation of the downstream injection method may use downstream swirl, extended spheroidization, or quenching. Downstream swirl refers to an additional swirling component that can be introduced downstream from the plasma torch to keep the powder away from the tube walls. Extended spheroidization refers to an extended plasma chamber to give the powder a longer residence time. In some implementations, this may not use downstream swirl, extended spheroidization, or quenching. In some embodiments, this may use one of downstream swirl, extended spheroidization, or quenching. In some embodiments, this may use two of downstream swirl, extended spheroidization, or quenching.

[0078] Powder injection from below can result in the reduction or elimination of the plasma tube coating in the microwave region. When the coating becomes too robust, microwave energy is protected from entering the plasma hot zone, reducing the plasma coupling. Occasionally, the plasma can even be extinguished and become unstable. The decrease in plasma intensity means a decrease in the level of powder spheroidization. Therefore, by supplying the raw material below the microwave region and ensuring a plasma plume at the outlet of the plasma torch, the coating in this region is eliminated, the microwave powder for the plasma coupling remains constant throughout the process, and appropriate spheroidization is enabled.

[0079] Therefore, advantageously, the downstream approach can operate the method over a long duration because coating issues are reduced. Further, the downstream approach allows the ability to inject more powder because there is no need to minimize the coating.

[0080] From the above detailed description, it will be recognized that the processing method of the present invention for mechanically alloyed powders and / or HEA powders is disclosed. Although some components, techniques, and aspects are described with a certain degree of particularity, it is clear that many changes can be made to the specific designs, configurations, and methods herein without departing from the spirit and scope of this disclosure.

[0081] Certain features described in this disclosure in the context of separate embodiments may also be implemented in a single They can be implemented in combination in practice. In contrast, various features described in the context of a single implementation can also be implemented separately in multiple implementations or in any sub - combination. Also, although a feature may be described above as acting in a certain combination, one or more features may be deleted from the combination in the claims in some cases, and the combination may be claimed as any sub - combination or a variation of any sub - combination.

[0082] Also, although a method may be shown in a particular order in the figures or described in the specification, such a method need not be implemented in the particular order shown or in a sequential order, and not all such methods need to be implemented to obtain the desired result. Other methods not shown or described may be incorporated into the example methods and processes. For example, one or more additional methods may be implemented before, after, simultaneously with, or in between any of the described methods. Further, the method may be reconfigured or rearranged in other implementations. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described components and systems may generally be integrated together into a single product or packaged into multiple products. Additionally, other implementations are within the scope of this disclosure.

[0083] Conditional language, such as "can," "could," "might," or "may," unless otherwise specifically recited or otherwise understood within the context in which it is used, generally conveys that certain embodiments may or may not include certain features, elements, and / or steps. Thus, such conditional language is generally not intended to imply that a feature, element, and / or step is required in any way for one or more of the embodiments.

[0084] Conjunctive language, such as the phrase "at least one of X, Y, and Z," is understood with the context as being generally used to convey that an item, term, etc. may be either X, Y, or Z, unless otherwise specifically recited. Thus, such conjunctive language is generally not intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0085] Languages to the extent used in this specification, such as the terms "approximately", "about", "generally", and "substantially", when used in this specification, represent values, amounts or characteristics that are close to the described values, amounts or characteristics that implement the desired function or still achieve the desired result. For example, the terms "approximately", "about", "generally", and "substantially" can refer to amounts within the range of 10% or less, 5% or less, 1% or less, 0.1% or less, and 0.01% or less of the described amount. When the described amount is 0 (for example, none, having none), the above-listed ranges may be specific ranges, within a specific % range of the value, for example, within the range of 10 wt. / vol.% or less, 5 wt. / vol.% or less, 1 wt. / vol.% or less, 0.1 wt. / vol.% or less, and 0.01 wt. / vol.% or less of the described amount.

[0086] Any particular feature, aspect, method, characteristic, feature, quality, attribute, element, etc. related to the various embodiments, the disclosure in this specification can be used in all other embodiments described in this specification. In addition, it should be recognized that any of the methods described in this specification may be practiced using any device suitable for performing the listed steps. Although numerous embodiments and their variations are described in detail, other modifications and methods of using them will be apparent to those skilled in the art. Therefore, it should be understood that various applications, modifications, materials, and substitutions may consist of equivalents without departing from the specific disclosure or claims of the invention herein.

[0087] While numerous embodiments and their variations are described in detail, other changes and methods of using them will be apparent to those skilled in the art. Accordingly, it should be understood that various applications, modifications, materials, and substitutions may consist of equivalents without departing from the specific disclosure or claims of the invention herein.

Claims

1. A method for producing spheroidized powder from mechanically alloyed raw materials, comprising: Preparing a mechanically alloyed powder raw material by mechanically pulverizing at least five elemental powders for 1 hour or more and 10 hours or less to mechanically alloy the at least five elemental powders; Introducing the mechanically alloyed powder raw material into a microwave plasma torch, a plasma plume of the microwave plasma torch, and / or an exhaust device of the microwave plasma torch; and At least partially melting and spheroidizing the mechanically alloyed powder raw material in the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch to form spheroidized powder A method comprising the steps of.

2. The method according to claim 1, wherein the mechanically alloyed powder raw material is mechanically pulverized by a ball mill.

3. The method according to claim 1 or 2, wherein the mechanically alloyed powder raw material contains Ti, Zr, Nb, Ta, Fe.

4. The method according to claim 1 or 2, wherein the mechanically alloyed powder raw material contains Al, Fe, V, Si.

5. The method according to claim 1 or 2, wherein the mechanically alloyed powder raw material contains Fe, Co, Ni, Cr, Ti.

6. The method according to claim 1 or 2, wherein the mechanically alloyed powder raw material contains Fe, Co, Ni, Cr, Al.

7. The mechanically alloyed powder raw material contains Fe, Co, Ni, Cr, Cu, the claim 1 or 2 of the methods described.

8. The method according to any one of claims 1 to 7, wherein the mechanically alloyed powder raw material contains a microstructure and the spheroidized powder maintains the microstructure.

9. After the step of introducing the mechanically alloyed powder raw material into a microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch, the following parameters: microwave power, plasma gas flow rate, gas type, plasma plume length, plasma plume diameter, plasma jet velocity, exhaust chamber pressure, quench gas, exhaust gas velocity, raw material velocity relative to the plasma jet velocity, supply gas flow rate, and raw material supply rate are further changed. The method according to any one of claims 1 to 8.

10. A method for producing spheroidized powder from a mechanically alloyed raw material, comprising: Preparing a mechanically alloyed powder raw material by mechanically grinding one or more precursors for 1 hour or more and 10 hours or less to form a high entropy alloy having a mixing entropy of more than 1.67R; Introducing the mechanically alloyed powder raw material into a microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch; and At least partially melting and spheroidizing the mechanically alloyed powder raw material in the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch to form spheroidized powder A method comprising.

11. The method according to any one of claims 10, wherein the mechanically alloyed powder raw material is mechanically ground by a ball mill.

12. The method according to claim 10 or 11, wherein the mechanically alloyed powder raw material contains Ti, Zr, Nb, Ta, Fe.

13. The method according to claim 10 or 11, wherein the mechanically alloyed powder raw material contains Al, Fe, V, Si.

14. The method according to claim 10 or 11, wherein the mechanically alloyed powder raw material contains Fe, Co, Ni, Cr, Ti.

15. The method according to claim 10 or 11, wherein the mechanically alloyed powder raw material contains Fe, Co, Ni, Cr, Al.

16. The method according to any one of claims 10 to 15, wherein the high entropy alloy contains five or more elements.

17. The method according to any one of claims 10 to 16, wherein the high entropy alloy comprises a non-equiatomic high entropy alloy.

18. After the step of introducing the mechanically alloyed powder raw material into the microwave plasma torch, the plasma plume of the microwave plasma torch, and / or the exhaust device of the microwave plasma torch, the following parameters: microwave power, plasma gas flow, gas type, plasma plume length, plasma plume diameter, plasma jet velocity, exhaust chamber pressure, quench gas, exhaust gas velocity, raw material velocity relative to the plasma jet velocity, supply gas flow rate, and raw material supply rate, further comprising a step of changing one or more of them. The method according to any one of claims 10 to 17.

Images