Fabrication of high-entropy alloy wire and multi-principal element alloy wire

Abstract

In various embodiments, metallic wires are fabricated by combining one or more powders of substantially spherical metal particles with one or more powders of non-spherical particles within one or more optional metallic tubes. The metal elements within the powders (and the one or more tubes, if present) collectively define a high entropy alloy of five or more metallic elements or a multi-principal element alloy of four or more metallic elements.

Claims

1. A method of fabricating a metallic wire comprising a high-entropy alloy comprising five or more metallic elements or a multi-principal element alloy comprising four or more metallic elements, the method comprising: providing a metallic tube comprising at least one of the metallic elements of the high-entropy alloy or the multi-principal element alloy; and combining, within the metallic tube, (i) one or more first metal powders each comprising a plurality of substantially spherical particles, and (ii) one or more second metal powders each comprising a plurality of non-spherical particles, the one or more second metal powders being mixed with the one or more first metal powders, thereby forming a wire preform, wherein (i) each first metal powder comprises at least one of the metallic elements of the high-entropy alloy or the multi-principal element alloy, (ii) each second metal powder comprises at least one of the metallic elements of the high-entropy alloy or the multi-principal element alloy, (iii) the substantially spherical particles are spherical to within ±10% in any direction such that an eccentricity in any direction does not exceed 10%, and (iv) the non-spherical particles (a) are elongated with an aspect ratio of at least 2:1, (b) are acicular, (c) have at least one flat surface, (d) are flakes, (e) have at least one corner or vertex, or (f) are polyhedral.

2. The method of claim 1, further comprising reducing a diameter of the wire preform via one or more mechanical deformation processes.

3. The method of claim 2, wherein the one or more mechanical deformation processes comprise at least one of drawing, pilgering, swaging, extrusion, or rolling.

4. The method of claim 2, further comprising: providing one or more sacrificial tubes around the metallic tube; and removing the one or more sacrificial tubes from the wire preform after the diameter of the wire preform is reduced.

5. The method of claim 1, wherein the metallic elements comprise at least four of Nb, Ta, Mo, W, Ti, Hf, V, Zr, Al, or Cr.

6. The method of claim 1, wherein at least one first metal powder is an elemental powder consisting essentially of one of the metallic elements.

7. The method of claim 1, wherein at least one first metal powder is an alloy powder consisting essentially of two or more of the metallic elements.

8. The method of claim 1, wherein at least one second metal powder is an elemental powder consisting essentially of one of the metallic elements.

9. The method of claim 1, wherein at least one second metal powder is an alloy powder consisting essentially of two or more of the metallic elements.

10. The method of claim 1, wherein the metallic tube consists essentially of one of the metallic elements.

11. The method of claim 1, wherein the metallic tube is an alloy tube consisting essentially of two or more of the metallic elements.

12. The method of claim 1, wherein the non-spherical particles of at least one second metal powder are angular flakes.

13. The method of claim 1, wherein an oxygen concentration of the one or more first metal powders is 300 ppm or less.

14. The method of claim 1, wherein an oxygen concentration of the one or more second metal powders is 300 ppm or less.

15. The method of claim 1, wherein at least one said first metal powder is provided by a process comprising: providing a plurality of metal particulates; feeding the metal particulates into a plasma, thereby at least partially melting the metal particulates; and cooling the at least partially melted metal particulates to form substantially spherical particles.

16. The method of claim 1, wherein at least one said second metal powder is provided by a process comprising: hydrogenating metal to form a metal hydride; mechanically grinding the metal hydride into a plurality of non-spherical particles; and dehydrogenating the non-spherical metal hydride particles.

17. The method of claim 1, wherein an average particle size of at least one of the first metal powders ranges from approximately 15 μm to approximately 45 μm.

18. The method of claim 1, wherein an average particle size of at least one of the second metal powders is greater than approximately 50 μm.

19. The method of claim 1, further comprising: translating a tip of the wire relative to a platform; thereduring, melting a tip of the wire with an energy source to form a molten bead comprising the metallic elements, whereby the bead cools to form at least a portion of a layer of a three-dimensional part; and repeating the above steps one or more times to produce the three-dimensional part, wherein the three-dimensional part comprises the high-entropy alloy or the multi-principal element alloy.

20. The method of claim 1, further comprising: providing one or more sacrificial tubes around the metallic tube before the one or more first metal powders and the one or more second metal powders are combined; and removing the one or more sacrificial tubes from the wire preform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:

(2) FIG. 1 is a schematic cross-sectional view of a plasma densification apparatus utilized to form spherical powder particles in accordance with various embodiments of the invention;

(3) FIG. 2A is a schematic cross-section of a wire preform in accordance with various embodiments of the invention;

(4) FIG. 2B is a schematic view of a wire being fabricated from a wire preform in accordance with various embodiments of the invention;

(5) FIG. 2C is a schematic cross-section of a wire preform containing multiple coaxial tubes in accordance with various embodiments of the invention;

(6) FIG. 3 is a schematic of an additive-manufacturing apparatus utilized to fabricate three-dimensional metallic parts in accordance with various embodiments of the invention;

(7) FIG. 4A is an axial cross-section of a wire fabricated in accordance with various embodiments of the invention;

(8) FIG. 4B is a longitudinal cross-section of the wire of FIG. 4A;

(9) FIG. 5 is a cross-sectional micrograph of a melted and resolidified multi-principal element alloy wire fabricated in accordance with various embodiments of the invention; and

(10) FIGS. 6 and 7 are cross-sectional micrographs of a melted and resolidified high-entropy alloy fabricated in accordance with various embodiments of the invention.

DETAILED DESCRIPTION

(11) In various embodiments of the present invention, a preform in the shape of, e.g., a rod or a bar, is provided by pressing and/or sintering a collection of powders. Collectively, the powders contain all of the elements of a desired HEA or MPEA. For example, one or more, or even all, of the powders may each be composed of particles that include, consist essentially of, or consist of one of the alloy's constituent elements. In other embodiments, one or more of the powders may each be composed of agglomerate particles including, consisting essentially of, or consisting of a mixture or alloy of two or more of the alloy's constituent elements.

(12) In accordance with various embodiments of the invention, the preform contains one or more powders composed of substantially spherical particles and one or more powders composed of non-spherical (e.g., flaky, angular, irregular, etc.) particles. For example, powder particles of tungsten and/or molybdenum (e.g., particles initially fabricated via a hydride/dehydride process or other process) may be plasma densified and may therefore be substantially spherical. An exemplary apparatus 100 for plasma densification is shown schematically in FIG. 1. As shown, powder particles 110 may be loaded into a powder feeder 120, which feeds the particles 110 through a plasma jet 130 formed by, for example, a time-varying current applied to an induction coil 140 sparking a plasma 150 from plasma gas 160 fed into the coil 140. The plasma jet 130 at least partially melts the particles 110, which subsequently resolidify into higher-density particles 170 collected below the plasma 150. The plasma-densified particles 170 are generally substantially spherical due to the plasma-induced melting and minimization of surface area resulting during resolidification. The minimization of the surface area of the particles also minimizes or substantially reduces the uptake of oxygen or other volatile species, and the plasma densification process itself volatilizes such species as well, thereby reducing the concentration of such contaminants within the powder 170. The plasma-densified powder particles 170 may have an average particle size of, for example, 15 μm to 45 μm, or even smaller.

(13) FIG. 2A depicts the fabrication of a wire preform 200 in accordance with embodiments of the present invention. One or more types of substantially spherical powder particles 170 are mixed with one or more powders of non-spherical particles 210 (e.g., within a tube 220 or in a cylindrical mold) such that all of the elements of the desired alloy are included within the preform 200. The non-spherical powder particles 210 may be formed by, e.g., a hydride/dehydride process. In various embodiments of the invention, the non-spherical powder particles are not rounded, oblong, ellipsoidal, and/or do not have smooth rounded surfaces along any portion of their surface areas. The non-spherical powder particles 210 may have an average particle size of, for example, less than or equal to 50 μm to 250 μm, or even larger. As mentioned above, either or both of the substantially spherical particles 170 or the non-spherical powder particles 210 may be individually composed of an alloy or mixture of two or more of the elements of the desired alloy. Such alloy powders may be formed via, e.g., hydride/dehydride of pre-alloyed ingots and optional plasma densification of powders resulting therefrom.

(14) In various embodiments, the melting point of one or more of the types of substantially spherical particles 170 is higher than the melting point of one or more of the types of non-spherical particles 210. In various embodiments, the ductility of one or more of the types of substantially spherical particles 170 is lower than the ductility of one or more of the types of non-spherical particles 210. In various embodiments, none of the metallic elements within the substantially spherical particles 170 are present within the non-spherical particles 210 and vice versa. In various embodiments, one or more of the metallic elements of the desired HEA are represented in both the substantially spherical particles 170 and the non-spherical particles 210. In some embodiments, both the substantially spherical particles 170 and the non-spherical particles 210 contain all of the metallic elements of the desired alloy, as elemental powder particles and/or alloy powder particles.

(15) The resulting mixture of substantially spherical particles 170 and non-spherical powder particles 210 within the preform 200 advantageously reduces or minimizes the amount of empty void space within the preform 200. The particles 170, 210 are preferably distributed within the preform 200 such that the composition of the preform 200 is substantially homogeneous along its length. In various embodiments, the preform 200 and/or at least a portion of the powder mixture therein may be further densified before further processing into wire. For example, the preform 200 and/or the powder mixture may be pressed by, e.g., hot isostatic pressing or cold isostatic pressing. The powder or the preform may be densified before and/or after inclusion of a sacrificial tube (as detailed below). After formation of the preform 200, the preform 200 is processed into a wire 230. In an exemplary embodiment depicted in FIG. 2B, the preform 200 is formed into wire 230 via drawing through one or more drawing dies 240 until the diameter of the wire 230 is reduced to the desired dimension. In various embodiments, various types of the particles of the preform 200, particularly those having relatively low ductility (e.g., molybdenum, tungsten, etc.) may have their morphologies deform during the processing of the preform 200 into wire 230. For example, substantially spherical particles 170 of molybdenum and/or tungsten may be elongated into oblong shapes or ribbons (e.g., along the wire axis), and/or they may remain substantially spherical in the final wire 230. Other types of particles having higher ductility (e.g., tantalum, niobium, etc.) may elongate around the other particles and form a matrix disposed around the harder particles in the final wire. In various embodiments, the drawing is supplemented with or replaced by one or more other mechanical deformation processes that reduce the diameter (or other lateral dimension) of the preform 200, e.g., pilgering, rolling, swaging, extrusion, etc. The preform 200 and/or wire 230 may be annealed during and/or after diameter reduction (e.g., drawing).

(16) In various embodiments, the preform 200 is formed via the combination of one or more substantially spherical powders 170 with one or more non-spherical powders 210 within a tube 220 that includes, consists essentially of, or consists of one or more of the elements of the desired HEA or MPEA. The tube 220 may itself be coaxially disposed within one or more other tubes 250 that include, consist essentially of, or consist of one or more other elements of the HEA, as shown in FIG. 2C. In such embodiments, the powders disposed within the tubes need not include the elements represented within the tube(s). When the preform 200 containing the one or more tubes is drawn down into wire 230, the cross-section of the wire 230 will thus include all of the elemental constituents of the desired alloy. In various embodiments, at least a portion of the powder mixture may be further densified before being placed into tube 220. For example, the powder mixture may be pressed by, e.g., hot isostatic pressing or cold isostatic pressing.

(17) In various embodiments, the one or more tubes may include, consist essentially of, or consist of one or more elements that are more ductile than one or more of the elements present in powder form. For example, the one or more tubes may include, consist essentially of, or consist of Nb, Ta, Ti, and/or Zr. In various embodiments, the one or more tubes have a sufficiently small diameter that the preform 200 itself may be utilized as the final wire 230 without further processing or diameter reduction such as wire drawing. In various embodiments, the one or more tubes, with the powders therewithin, may be annealed and/or subjected to pressure (e.g., hot-isostatically pressed) before (or between multiple steps of) the process of diameter reduction. Such treatment may advantageously reduce void space within and increase the density of the final wire 230.

(18) In various embodiments, the melting point of one or more of the types of substantially spherical particles 170 and/or one or more of the types of non-spherical particles 210 is higher than the melting point of one or more of the metallic elements of one or more of the tubes 220, 250. In various embodiments, the ductility of one or more of the types of substantially spherical particles 170 and/or one or more of the types of non-spherical particles 210 is lower than the ductility of one or more of the metallic elements of one or more of the tubes 220, 250. In various embodiments, none of the metallic elements within the substantially spherical particles 170 and/or the non-spherical particles 210 are present within the tubes 220, 250 and vice versa. In various embodiments, one or more of the metallic elements of the desired alloy are represented in at least one of the types of substantially spherical particles 170 and/or at least one of the types of non-spherical particles 210, as well as in one or more of the tubes 220, 250.

(19) In other embodiments, the preform 200 may include, consist essentially of, or consist of a sacrificial tube 220 in which the various powders 170, 210 are disposed. After processing of the preform 200 into wire 230, the sacrificial tube 220 may be etched or melted away, and the final wire 230 includes, consists essentially of, or consists of the elements of the desired alloy arising solely from the original powders 170, 210. In various embodiments, one or more tubes to be processed as part of the wire may be disposed within the sacrificial tube 220; at least portions of such tubes will typically remain as portions of the wire after removal of the sacrificial tube 220. The sacrificial tube 220 may include, consist essentially of, or consist of, for example, plastic, rubber, one or more polymeric materials, a metallic material having a melting point lower than one or more (or even all) of the metallic elements within the powders 170, 210, a metallic material selectively etchable (i.e., over the metallic elements within the powders 170, 210 and other tubes), etc.

(20) Once wire 230 including, consisting essentially of, or consisting of the elemental constituents of a desired HEA or MPEA is fabricated in accordance with embodiments of the invention, the wire 230 may be utilized to fabricate a three-dimensional part with an additive manufacturing assembly 300. For example, as shown in FIG. 3, the wire 230 may be incrementally fed, using a wire feeder 310, into the path of a high-energy source 320 (e.g., an electron beam or a laser beam emitted by a laser or electron-beam source 330), which melts the tip of the wire 230 to form a small molten pool (or “bead” or “puddle”) 340. The entire assembly 300 may be disposed within a vacuum chamber to prevent or substantially reduce contamination from the ambient environment.

(21) Relative movement between a substrate 350 (which may be, as shown, disposed on a platform 360) supporting the deposit and the wire/gun assembly results in the part being fabricated in a layer-by-layer fashion. Such relative motion results in the continuous formation of a layer 370 of the three-dimensional object from continuous formation of molten pool 340 at the tip of the wire 230. As shown in FIG. 3, all or a portion of layer 370 may be formed over one or more previously formed layers 380. The relative movement (i.e., movement of the platform 360, the wire/gun assembly, or both) may be controlled by a computer-based controller 380 based on electronically stored representations of the part to be fabricated. For example, the two-dimensional layers traced out by the melting wire may be extracted from a stored three-dimensional representation of the final part stored in a memory 390.

(22) The computer-based control system (or “controller”) 380 in accordance with embodiments of the present invention may include or consist essentially of a general-purpose computing device in the form of a computer including a processing unit (or “computer processor”) 392, the system memory 390, and a system bus 394 that couples various system components including the system memory 390 to the processing unit 392. Computers typically include a variety of computer-readable media that can form part of the system memory 390 and be read by the processing unit 392. By way of example, and not limitation, computer readable media may include computer storage media and/or communication media. The system memory 390 may include computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) and random access memory (RAM). A basic input/output system (BIOS), containing the basic routines that help to transfer information between elements, such as during start-up, is typically stored in ROM. RAM typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit 392. The data or program modules may include an operating system, application programs, other program modules, and program data. The operating system may be or include a variety of operating systems such as Microsoft WINDOWS operating system, the Unix operating system, the Linux operating system, the Xenix operating system, the IBM AIX operating system, the Hewlett Packard UX operating system, the Novell NETWARE operating system, the Sun Microsystems SOLARIS operating system, the OS/2 operating system, the BeOS operating system, the MACINTOSH operating system, the APACHE operating system, an OPENSTEP operating system or another operating system of platform.

(23) Any suitable programming language may be used to implement without undue experimentation the functions described herein. Illustratively, the programming language used may include assembly language, Ada, APL, Basic, C, C++, C*, COBOL, dBase, Forth, FORTRAN, Java, Modula-2, Pascal, Prolog, Python, REXX, and/or JavaScript for example. Further, it is not necessary that a single type of instruction or programming language be utilized in conjunction with the operation of systems and techniques of the invention. Rather, any number of different programming languages may be utilized as is necessary or desirable.

(24) The computing environment may also include other removable/nonremovable, volatile/nonvolatile computer storage media. For example, a hard disk drive may read or write to nonremovable, nonvolatile magnetic media. A magnetic disk drive may read from or writes to a removable, nonvolatile magnetic disk, and an optical disk drive may read from or write to a removable, nonvolatile optical disk such as a CD-ROM or other optical media. Other removable/nonremovable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The storage media are typically connected to the system bus through a removable or non-removable memory interface.

(25) The processing unit 392 that executes commands and instructions may be a general-purpose computer processor, but may utilize any of a wide variety of other technologies including special-purpose hardware, a microcomputer, mini-computer, mainframe computer, programmed micro-processor, micro-controller, peripheral integrated circuit element, a CSIC (Customer Specific Integrated Circuit), ASIC (Application Specific Integrated Circuit), a logic circuit, a digital signal processor, a programmable logic device such as an FPGA (Field Programmable Gate Array), PLD (Programmable Logic Device), PLA (Programmable Logic Array), RFID processor, smart chip, or any other device or arrangement of devices that is capable of implementing the steps of the processes of embodiments of the invention.

(26) Advantageously, wires in accordance with embodiments of the invention are substantially homogeneous in composition. Thus, all of the elements of the desired HEA or MPEA are present in each small molten pool 340 of material at any particular instant during fabrication. Due to their small size, the pools 340 cool quickly, locking in the desired alloy composition. In addition, since empty void space within the wire 230 fabricated in accordance with embodiments of the present invention was substantially eliminated via packing of powder particles with multiple different shapes and/or sizes, the wire 230 melts during additive manufacturing with little if any sparking and without introducing porosity, cracks, or other defects into the printed part. After the additive manufacturing process is complete, the part may be removed from the platform and subjected to final machining and/or polishing.

Example

(27) A substantially pure Cu tube having a 0.648 inch outer diameter and a 0.524 inch inner diameter was wrapped around a Ta-3 W (i.e., Ta—W alloy containing approximately 3% W) welded tube having an outer diameter of 0.500 inch and an inner diameter of 0.470 inch. A powder blend of 4 weight percent Ta non-spherical powder particles, 32 weight percent Nb non-spherical powder particles, 32 weight percent Mo substantially spherical powder particles, and 32 weight percent W substantially spherical powder particles was utilized to fill the Ta-3 W tube at an apparent fill density of approximately 51%. The Ta and Nb powder particles were low-oxygen powder particles formed by a hydride-dehydride process and thus had the form of angular flakes. The Mo and W powder particles were formed via a plasma densification process. Taking into account the Ta-3 W tube, the preform within the Cu tube contained 24.3 atomic percent Ta, 25.7 atomic percent W, 25.0 atomic percent Mo, and 25.0 atomic percent Nb. In total, 390 grams of powder were utilized.

(28) The ends of the Cu tube were sealed with Cu plugs, and the assembly was cold swaged to 0.069 inch diameter in about 20 steps ranging from 5% to 25% area reduction per pass, depending upon the available swage diameter for each pass. To minimize powder slip within the tube, the rod was swaged along one-half of its length, flipped, and then swaged from the opposite end until the whole assembly had a substantially uniform diameter. Including the Cu tube and plugs, the starting weight was about 935 grams, and the assembly produced more than 600 linear inches of wire (approximately 100:1 total area reduction). FIGS. 4A and 4B are, respectively, axial and longitudinal cross-sectional micrographs of the wire at a diameter of 0.084 inch. As shown, some of the initially substantially spherical powder particles remain substantially spherical, while others have elongated along the long axis of the wire due to the mechanical deformation. In general, the softer Ta and Nb powder particles have elongated around the harder Mo and W powder particles.

(29) The Cu-sheathed wire was continuous and could be coiled to a diameter of 13 inches without breaking. The Cu sheath was removed prior to testing. For testing, lengths of the wire each having a length of 3 inches were cut and acid etched in a mixture of 25% nitric acid and 75% distilled water until all of the Cu was removed. In order to simulate the high-speed melting and resolidification of an additive manufacturing process, wire sections totaling 32 grams in weight were placed in a cold Cu hearth, and an electric arc from a W electrode supplied sufficient energy to melt the wire. The Cu hearth rapidly cooled the metal, thereby closely approximating the high rate of cooling in additive manufacturing. A second set of samples included sufficient pure V added to the hearth to produce a 20%-20%-20%-20%-20% (atomic percent) HEA of V—Nb—Ta—Mo—W. This second set of samples could also have been produced via inclusion of the proper amount of substantially spherical or non-spherical V powder particles within the starting Ta-3 W tube. All of the samples produced in accordance with this example melted readily into a substantially homogenous mixture of their constituent elements and resolidified as a single solid solution phase. Moreover, all of the samples melted very gently and quietly (i.e., with minimal or no splattering, spitting, etc.), despite their origins as powder blends; thus, embodiments of the present invention have sufficiently high density and sufficiently low concentrations of volatile contaminants to ensure compatibility with additive manufacturing, welding, and other rapid melting and solidification processes.

(30) Scanning electron microscopy (SEM) energy dispersive X-ray spectrometry (EDS) was performed on one of the second set of samples, and the average composition of the five-element HEA was (22.6%-26.1%) W, (18.8%-20.6%) Ta, (18.8%-19.3%) Mo, (14.8%-16.0%) Nb, and (19.7%-23.3%) V, where all compositions are atomic percentages. Via SEM analysis, the samples were determined to be single-phase with the expected dendritic microstructure, and the inter-dendrite spacing ranged from approximately 10 μm to approximately 20 μm. FIG. 5 is a cross-sectional micrograph of one of the first set of samples after melting and resolidification. The sample was chemically etched to reveal the internal structure. As shown, some grain structure is visible with internal dendritic structure. The sample was swab-etched (as opposed to being fully immersed) with an etchant prepared from 5 ml lactic acid, 5 ml hydrogen peroxide, 2 ml hydrofluoric acid, and 2 ml nitric acid. FIGS. 6 and 7 are cross-sectional micrographs of one of the second set of samples after melting and resolidification. The sample in FIG. 6 was also chemically etched (with the same etchant detailed above with reference to FIG. 5) to reveal the internal structure, and the sample in FIG. 7 was polished but not chemically etched. The dendritic microstructure of the sample is quite evident.

(31) Finally, multiple Vickers hardness tests using a 1 kg load were performed on the first and second sets of samples, and the results obtained are included in the table below.

(32) TABLE-US-00001 Hardness Hardness Hardness Composition (Test 1) (Test 2) (Test 3) Nb—Ta—Mo—W 490 533 524 V—Nb—Ta—Mo—W 561 579 591
As expected, the second set of samples exhibits larger hardness values due to the addition of V into the alloy. The hardness values for both sets of samples are fairly high and imply high tensile strength of wires fabricated in accordance with embodiments of the present invention.

(33) The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.