Production of substantially spherical metal powders
A method for producing a substantially spherical metal powder is described. A particulate source metal includes a primary particulate and has an average starting particle size. The particulate source metal is optionally ball milled and mixed with a binder in a solvent to form a slurry. The slurry is granulated to form substantially spherical granules, wherein each granule comprises an agglomeration of particulate source metal in the binder. The granules are debinded at a debinding temperature to remove the binder from the granules forming debinded granules. The debinded granules are at least partially sintered at a sintering temperature such that particles within each granule fuse together to form partially or fully sintered solid granules. The granules can then be optionally recovered to form a substantially spherical metal powder.
1. A method for producing a substantially spherical metal powder comprising:
providing a particulate source metal including a primary particulate and having an average starting particle size, wherein the particulate source metal comprises titanium, titanium hydride, Al—V master alloy, titanium oxide, or mixtures thereof;
mixing the particulate source metal with a binder and an optional solvent to form a slurry;
granulating the slurry to form substantially spherical granules, wherein each granule comprises an agglomeration of particulate source metal;
debinding the granules at a debinding temperature to reduce a binder content of the granules forming debinded granules;
at least partially sintering the debinded granules at a sintering temperature such that particles within each granule fuse together to form partially or fully sintered granules; and
recovering the sintered granules to form the substantially spherical metal powder.
2. The method of claim 1 , further comprising sorting the granules by size.
3. The method of claim 1 , wherein the substantially spherical metal powder has an average final particle size from about 1 to about 1000 micrometers.
4. The method of claim 1 , wherein the substantially spherical metal powder has an average particle aspect ratio less than about 1.5.
5. The method of claim 1 , wherein the particulate source metal further comprises zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, nickel, aluminum, iron, alloys of the above metals with each other, alloys of the above metals with metals, alloys of the above metals with non-metals, CP—Ti alloy, Ti-6Al-4V alloy, nickel-based high temperature alloys, stainless steel, hydrides thereof, oxides thereof, mixtures thereof, or combinations thereof.
6. The method of claim 1 , further comprising making the particulate source metal from a raw material selected from titanium slag, upgraded titanium slag, titanium dioxide, scrap titanium, scrap titanium alloy, or a combination thereof.
7. The method of claim 1 , wherein the average starting particle size of the primary particulate is from 0.1 to 100 micrometers.
8. The method of claim 1 , wherein mixing the particulate source metal with a binder further comprises wet ball milling the particulate source metal and the binder in the solvent.
9. The method of claim 1 , wherein granulating the slurry comprises spray drying, rotary drying, vibratory pelletizing, freeze granulation and drying, or combinations thereof.
10. The method of claim 1 , wherein the granules have an average granule size from about 20% to about 50% larger than an average final particle size of the substantially spherical metal powder.
11. The method of claim 1 , wherein the granules have an average granule size greater than 10 micrometers.
12. The method of claim 1 , wherein the debinded granules are mixed with CaO powder such that granules are separated by CaO powder during sintering.
13. The method of claim 1 , wherein sintering the debinded granules is performed until each sintered granule reaches a relative density greater than 65%.
14. The method of claim 1 , wherein sintering the debinded granules is performed such that each sintered granule is substantially free from bonding to each other.
15. The method of claim 1 , wherein sintering the debinded granules is performed until the debinded granules fuse together at contact points between the debinded granules but the debinded granules retain at least about 20% unfused surface area on average.
16. The method of claim 1 , wherein the at least partially sintering is performed such that the granules are connected to each other forming a frangible body of at least partially sintered granules; and wherein the separating is accomplished by breaking the frangible body to recover the substantially spherical metal powder.
17. The method of claim 16 , wherein breaking the frangible body comprises ball milling the frangible body.
18. The method of claim 1 , further comprising deoxygenating the sintered granules using a de-oxygen agent sufficient to reduce oxygen content to less than 0.3% by weight.
19. The method of claim 18 , wherein the de-oxygen agent comprises at least one of calcium (Ca) and calcium hydride (CaH 2 ).
20. The method of claim 18 , further comprising mixing the sintered granules and the de-oxygen agent with a salt before de-oxygenating the granules.
21. The method of claim 18 , wherein the de-oxygen agent is a salt comprising a calcium halide salt, a calcium halide-alkali halide eutectic salt, a calcium halide-calcium halide eutectic salt, or combination thereof.
22. The method of claim 18 , the de-oxygen agent is a eutectic salt composed of CaCl 2 and KCl.
23. The method of claim 18 , wherein de-oxygen agent comprises a eutectic salt with a melting point below a melting point of calcium (Ca).
24. The method of claim 18 , wherein de-oxygen agent removes oxygen from the debinded granules during sintering, and wherein the sintered granules remain separate from each other during sintering.
25. A method for producing a substantially spherical metal powder comprising:
providing a particulate source metal including a primary particulate and having an average starting particle size;
mixing the particulate source metal with a binder and an optional solvent to form a slurry;
granulating the slurry to form substantially spherical granules, wherein each granule comprises an agglomeration of particulate source metal;
debinding the granules at a debinding temperature to reduce a binder content of the granules forming debinded granules;
at least partially sintering the debinded granules at a sintering temperature such that particles within each granule fuse together to form partially or fully sintered granules, wherein the debinded granules are mixed with CaO powder such that granules are separated by CaO powder during sintering; and
recovering the sintered granules to form the substantially spherical metal powder.
26. The method of claim 25 , wherein the substantially spherical metal powder has an average particle aspect ratio less than about 1.5.
27. A method for producing a substantially spherical metal powder comprising:
providing a particulate source metal including a primary particulate and having an average starting particle size;
mixing the particulate source metal with a binder and an optional solvent to form a slurry;
granulating the slurry to form substantially spherical granules, wherein each granule comprises an agglomeration of particulate source metal;
debinding the granules at a debinding temperature to reduce a binder content of the granules forming debinded granules;
at least partially sintering the debinded granules at a sintering temperature such that particles within each granule fuse together to form partially or fully sintered granules;
deoxygenating the sintered granules using a de-oxygen agent sufficient to reduce oxygen content to less than 0.3% by weight, wherein the de-oxygen agent is a eutectic salt composed of CaCl 2 and KCl; and
recovering the sintered granules to form the substantially spherical metal powder.
28. The method of claim 27 , wherein the substantially spherical metal powder has an average particle aspect ratio less than about 1.5.
29. The method of claim 27 , wherein sintering the debinded granules is performed until each sintered granule reaches a relative density greater than 65%.