US2287771A - Production of powdered alloys - Google Patents

Description

Patented June 1942 V c V Peter P. AlexandenMarblehead, Mass. I

No Drawing. Application J nuary 9', 1940,

I, Serial No. 313,116

H h V 6 ciaii sulcl, 75-415) This inventi rlelates to thefproductionofg powdered alloys} and more especially to thepro duction of finely divided powdered alloys of the refractory and other metals with one another or with carbonyiron, nickel and cobalt.

The ,formation of alloys of the refractory metals, is, in, general, well known ,and may be brought about, for example, in theelectric furpermit only the weldingand diffusion of adjacent particles and prevent" the coagulation and sintering of the particles of the alloy or its constituents gintolargermasses. f j

, The variousphasesof the processare carried out, in a relatively simple manner as follows:

nace. Howeve'nthe production of alloys of these metals in theform of finely divided powders capable of passing, say 2 00 mesh or better, is attended with considerable difficulty. -Generally speaking, the alloys are extremely hard and, when produced according to any known or previously used process, take the form atbestof large particleswhichimust be 'ground tofproduce the degree of fineneSsnecessary (for many industrial purposes, a" diflicult operation. If the metals in The powdered oxide, for example, of one of the refractory metals which is to form a part of -the alloy,ris thoroughly mixed with the alloying metal in powdered form. A powdered metalhydride, forexample calcium hydride, is added to the mixture in sufficient amount to carry out the reactions hereinafter described, the whole being thoroughly, mixed so that the particles of the temperature raised untilthe metal hydride disthe form of line powders aresimply fused ,to-

gether they form large particles or even blocks of extreme hardness, thedifiicultyof reducing the latter toifine'powders being even greater. v

According to the present invention,powdered or betterI are-produced without"thefnecessity"of subjecting the same crushing orgrinding operationsx h The process of the invention does not depend, i for fineness, in size "of the powdered alloysproducedthereby, upon the degree of preliminary crushing and grindingof the metals entering into the alloys.; While the process is carried out with powdered and thoroughly mixed materials, nevertheless the particles of the final alloy are much smaller and more uniform in sizethan those of about in the processby the decomposition of the initial mixture which, in the preferredform is ac complished partly by the introduction of one of the metals, into the initial mixture, in the form of an oxidawhichis reduced at a temperature below the fusion temperature of the metal, and

partly through ,tthe formation, during the early,

heating stages iofwthe process, of complex cbrripounds of the other metal which are reduced or otherwise broken up at 'low temperatures below the point of fusion of either alloying metal.

In orderthatthefine particles of metalltmay uniteto form fitre particles of alloy, the"procels s is further characterized by the fact that it is car-f ried out under conditions wherein the atmosphere powdered metal hydride are scattered through the mass of powdered metal" and oxide. 1 The powdered charge is' placed in a furnace andthe sociates:forming nascenthydrogen and the metal released from the hydride, theflatter being in a nascent state. Inasmuch as the density of cal- ,cium hydride is '13 andthat of metallic calcium 1.55:,it will be'apparent' that after" dissociation the released calcium occupies a larger volume than the calcium, hydride. There willtherefore be an expansion of every particle whichprevi ouslywas composed of calciumhydride, this expansion pushingthe adjacent particles of metallic oxide and metal together, At the same time the largelvolume of evolving hydrogenin the mass produces a further, movement ofthe"particles the, initial powderednmaterials. This is brought towards one another. As the hydrogen evolves infthe mass it also reduces the metallic oxide to particles of metal and oxygength latter uniting with the hydrogen to formtsteam which is im.- mediately reducedby the calcium, the latter unit ing with the oxygen to form calcium oxide While the hydrogenescapes. V c The density of the calcium oxide ismu'ch greaterthen that of the calcium so that there is now a contraction of the particles which were originally calcium hydride, the calcium' oxide forming a spongy mass comprising countless ele- 'mental crucibles surrounding'the particles of the metals which, duringthe continued application of 'heat arewelded together and diffuse-[into {one is highly reducing and free from oxygen, thus preventing surface oxidation of the particles of the metals which; being free from oxide, may

weld and difiuse into one another. Moreover, 1 the processis characterized by the fact that there}, is brought about; duringone phase thereof, a oertain amount of movemeht ofthe metallicpar ticles towards one another which isaccompanied by the formation of a spongy spacer which will another, the presence of the highly reducing hydrogen in the masspreventing the formation of surface'oxides on the metallic particles so that the welding and diffusion maytak'e place. Sintering of adjacentparticles of alloy into a spongy mass .or intolarger particles is prevented by the surrounding calcium oxide.

a further aid to the understandingof t e invention I will now describe theforinat'ion of a specific powdered alloymade inaccordance with the invention, in this instance titaniurn fcarbide.

Powdered calcium hydride and powdered titanium oxide are thoroughly mixed with powdered carbon, preferably in the iform of 1 lamp black. r

gether, the application of heat being continued until the particles of welding titanium and carbon 'diil'use into one another forming finely divided particles of titanium carbide. The reaction may be expressed as follows:

Tiz+2CaHz+C=TiC+2CaO+2H2 When the reaction is complete the calcium oxide may be removed in any well known manner, for example, by leaching, leaving powdered titanium carbide.

As far asI am now aware the process is more or less limited to the use of calcium, strontium and barium hydrides as reducing-spacer-forming agents as other reducing agents, such as aluminum, will readily combine with one or more of the metals to be alloyed and furthermore the heat of reaction during the first stage would be so great that the whole mass would be fused. In the case of calcium, strontium and barium hydrides the heat of reaction is very much lower 50 that the whole process is carried out below the point of fusion and therefore the material comes in fine solid particles of alloy. It is possible that other reducing spacer-forming agents may be substituted for those enumerated but in commercial operation I prefer to use calcium hydride as the other agents have no marked advantage over calcium hydride whereas the latter is much cheaper commercially than barium Or strontium hydrides. Moreover calcium hydride may be prepared according to the method disclosed and claimed in my prior Patent No. 2,082,134, issued June 1, 1937, it being immaterial, insofar as the must be continued to eflect diffusion of the particles into one another will vary in accordance with the metals of the group which are selected to form the alloy.

While I have described my process with great particularity, it will be understood that the same may be varied within the spirit of the invention and the scope of the appended claims.

What I claim is:

l. The process of forming powdered alloys consisting of a metal selected from a first group consisting of titanium, zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum, chromium and beryllium and an alloying element selected from a second group consisting of titanium, zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum, chromium, beryllium, carbon, nickel, iron and cobalt which comprises thoroughly mixing a powdered oxide of the metal of the first group with powdered calcium hydride and the alloying element of the present method is concerned, whether or not all traces of magnesium oxide are removed.

There are further apparent limitations of the process, namely, that the alloying metals must combine more readily with one another than with the metal liberated from the reducing-spacerforming agent, thus, while the metals, titanium, zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum, chromium and beryllium may be alloyed with one another or with carbon, nickel, iron and cobalt, in accordance with the process, they may not be alloyed with silicon, copper and magnesium, which combine and form stable compounds with calcium.

During the early heating stages, before the calcium hydride is reduced to calcium and hydrogen, it is probable that the powdered metal forms complex compounds with the calcium hydride, these compounds breaking up as the temperature increases. I donot commit myself as to the nature of these compounds. Suifice it to say that the formation of such compounds accounts partly for the fact that the size of the particles of the final alloy is, in general, much smaller and more uniform than the powdered oxide and powdered metal of the initial mixture.

It will be understood by those skilled in the art that the length of time that the heat treatment second group in powdered form, raising the temperature of the mixture to the point where the hydrogen is liberated from the calcium hydride, the liberated hydrogen reducing the metal oxide whereupon the calcium combines with the oxygen to form calcium oxide, and thereafter further raising the temperature to the point where the metal liberated from the oxide diifusesinto the alloying element from the second group.

2. The process of forming powdered alloys consisting of a metal selected from a first group consisting of titanium, zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum, chromium and beryllium and an alloying element selected from a second group consisting of titanium, zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum, chromium, beryllium, carbon, iron, nickel and cobalt which cium hydride, barium hydride and strontium hytemperature of the mixture to liberated from the second group. V

3. The process according to claim 1 in which the amounts of powdered oxide and alloying elements are varied in accordance with the desired percentages in the final alloy whereas the amount of'calcium hydride is varied'in accordance with the amount of the metal oxide present.

according to claim 2 in which after difiusion of the PETER- P. ALEXANDER.