US2921861A - Method of forming titanium silicide refractory articles - Google Patents

Description

p: thaw bodies by casting without pressure.

2,921,861 Patented Jan. 19, 1960 EQQ METHOD OF FQRMING TITANIUM SI LICIDE REFRACTORY ARTICLES Ralph F. Wehrmann and Stanley Kluz, Waukegan, Ill.,

assignors to Fansteel Metallurgical Corporation, a corporation of New York No Drawing. Application August 19, 1953 Serial No. 375,304

10 Claims. (Cl. 106-55) Our invention relates to a titanium silicide composition formed into shaped bodies and to a method of producing the same.

More particularly, this invention relates to non-porous shaped bodies of titanium silicides such as titanium disilicide, TiSi and other compounds, alloys or intermetallic compositions of titanium and silicon, such as Ti Si formed into shaped bodies of the character of bars, rods, tubes, plates, discs, pellets and the like, or irregular shapes of high compressive strength and density, substantially free of porosity and oxidizable impurities, as well as binder substances of organic and inorganic character which differ in chemical and physical properties from the silicides of titanium, and to methods of forming the same.

Silicides of titanium such as TiSi or Ti Si desirably produced in the form of dense, non-porous shaped bodies according to the present invention have a high degree of resistance to oxidation in air at elevated temperatures, as Well as erosion by other hot gases, have great hardness and compressive strength, as well as wear resistance, and thereby have outstanding utility in oil'burner and rocket nozzles, nozzles in artillery pieces, electrical resistance elements, component parts for jet engines, turbine blades and buckets, and furnace elements, as well as analogous useswherein such properties are necessary or desirable.

Shaped titanium silicides are of very light weight and therein have advantage in some of these uses over other silicide bodies.

In a co pending application of Beidler and Campbell, Serial No. 150,541, filed March 8, 1950, now Patent No. 2,665,474, molybdenum-silicon alloys or intermetallic compositions are described as being formed into shaped It was found that such products are inferior to products obtained by the present invention for certain uses requiring substantial compressive strength and wear resistance. Moreover, even in uses where only the property of titanium silicides to resist oxidation in air is necessary, the hardened nonporous products of the present invention are superior, not only for their inherent capacity to resist oxidation at raised temperatures, but also because of the nonporous mechanical structure obtainable. The shaped bodies of the present invention tend to resist permeation into their internal structure of such oxidizing gases, and thereby have a longer life under oxidizing conditions as compared to products not having this structure.

According to the present invention, it is found that if silicides of titanium are reduced to an extremely fine particle size such as of the order of 0.5 to 5 microns, the silicide powder without binder or sometimes upon being first mixed with a solid organic binder substance and then compressed under great pressure usually exceeding about 5 tons per square inch, such as from 5 to 60 tons per square inch, usually 5 to 40 tons per square inch when a binder is used, may be sintered to the integral mass as shaped in the pressing to a density greater than I 95% of the theoretical, to producea shaped body having utility as stated above. The specific gravity of titamum disilicide theoretically is 4.13 grams per cc. As will be 2 apparent to a skilled worker in the art, this figure will vary with variationsof Ti-Si proportions whereby a. content of other compounds of titanium and silicon .or alloys or intermetallic compositions of titanium silicon may be present, or another compound of titanium. and silicon such as Ti Si is used. The final products of the present invention, usually of a density in the range of 3.8 to 4.1 grams per cc., have great compressive strength and hardness, are non-porous, wear resistant, and resistant to oxidation in air at high temperatures, such as about 1000 to 2000 C., for long periods of time.

Compounds of silicon and titanium such as TiSi and Ti Si are produced bymixing and sintering titanium or titanium hydride and silicon powders. Such powdered elements are preferably in stoichiometric proportions to produce titanium disilicide TiSi or Ti Si They may, however, be .in other proportions to produce a composition predominant in TiSi and containing substantial quantities of Ti Si or other titanium silicides to vary some of the TiSi properties, particularly the sintering temperature thereof. Atitanium-silicon system tends to have its sintering temperature raised in proportion to the content of high sintering Ti Si therein. Proportions adjusted to produce the titanium disilicide is preferred because this silicide composition has the greatest resistance to oxidation in air at high temperatures. However, there is substantial resistance to oxidation in other titanium silicides either in the form of puresilicide compounds such as Ti Si or in the form in which they maybe present in homogeneous admixture with TiSi Thus the silicon may be present in proportions exceeding, or less than, that required to form TiSi Accordingly, in the broadest'aspect of this invention, the silicon and. titanium may be adjusted in proportions to a ratio of about three atomic proportions of silicon toone of titanium, down to about three atomic proportions of silicon to five of titanium. However, as stated, preferred proportions are two atoms of silicon per atom of titanium. Percentagewise, the silicon in the silicon-titanium com-' position may' be mixed in proportions of about 26 to 64% by weight of the mixture with titanium, and to form the. preferred 2:1 atomic proportion mix corresponding to titanium disilicide, the silicon will be about 54% by weight of the mix. 1 1 i In forming the silicides of titanium the elemental powders silicon and titanium, first homogeneously mixed, are heated to a temperature in the range of about 1200? to 2000 C., preferably in the lower part ofthe range,- about 1300" C., to form titanium disilicide, and con-- siderably higher where increasing quantities of high sintering titanium silicides corresponding to Ti Si are pres, ent. Such reaction is effected in a non-oxidizing atmosphere which preferably is free of carbon, such as carbon. monoxide, to avoid contamination of the product with; carbon, which forms carbides of these elements and re-; duces resistance of the product to'oxidation in air. Thus, a preferred non-oxidizing atmosphere is hydrogen or inert. gases like helium or argon. After cooling the silicon and titanium reaction product, it is comminuted to a powder of a size less than about 325 mesh. It is then further finely milled, with or without the organic substance as hereinafter described, in a ball mill to produce evenly shaped powdered particles, which are desirably equiaxed f grains as compared to acicular-shaped particles, the former being preferred because particles of such shape allow more even pressure-transfer in the pressing thereof to form dense, non-porous shaped bodies. The powderformed in the ball mill is in the critical particle size range of 0.5 to 5 microns, preferably about 1 micron plus or minus 0.2 micron.

1 powder.

preferab y carbonaceous residue; particularly preferred for this property are the alkyd resins. Such resin will be understood to be atemporary bonding resin which functions to flow under pressure to enhance the even transfer of pressure hydrostaticallyto all particles and to firmly adhere the compressed powder. Alkyd resins are quite superior since they flow under pressure, securely bond the particles, and leave no carbonaceous residue when heatedabove aboutg 600 C. Thermosetting resins such as Bakelite are unsuitable. Typical alkyds are such as are formed by a reaction of a polybasic organic acid or anhydride such as ,phthalic acid, succinic acid, adipic acid, etc., with a polyhydroxy aliphatic alcohol such as glycerine, ethylene glycol, etc., of which the reaction product of phthalic anhydride with glycerine ie. Glyptal resin, is preferred. Additionally, volatilizable 'and/ or decomposable waxeswhichdonot leave acarbonaceous residue are useful as a temporary binder, of which paraffin wax, Acrawax and stearic acid are typical;

that they tend to flow under pressure and allow even 7 pressure-transfer, which may be enhanced by the presence 'of a thermoplastic resin or wax, the organic substance further serving as a temporary binder to allow handling during the subsequent step ofsinteriug to form an integral,".dense,,non-porous shaped body thereof, as described above. 7

'It is often desirable to omit the organic binder substance,- in accordance with the present invention, if powder is maintained at about 1 micron or less, preferably between about 0.5 to 0.8 micron, since powdered par ticles in this critical particle size range may be packed to the desired density and cohesion at high pressures,

such as about to 60 tons per square inch. The resulting form-sustaining compact may be sintered to the desired integral and defense form by placing the compact(withoutpreheating) in the hottest part of a hydro.-

, gen (or other non-oxidizing, non-carbonaceous) atmos- The waxvand some soft forms of resin which do not become tacky may be milled in solid form for homogeneous' distribution into and about the titanium silicide For: better tion, the solid binder substance may be firstdissolved in a volatile solvent such'as a ketone, i.e. acetone, or a hydrocarbon solvent such as petroleum-or coal tar naph tha andmixed with powdered particles of the silicide to form adamp powder, a wet paste or a slurry, and the solvent then evaporated to leave a binder coating of the resin or wax about the powdered silicide particles. Where thepowdered silicide particles after coating with the binder are not sufficiently fine, they maybe further milled in the presence of the binder to the critical particle size above stated. a y

-The powder mass, together with the binder coating homogeneously applied thereto, is then placed in thedie' of a press-which, if desired, maybe coatedwith a lubri cant such as stearic'acid, and then subjectedto a preformingsand shaping pressure of at least about 5 tons per square inch, suchas from :5 -to"40 tons per'square inch, to form adense, non-porous, shaped product. The shaped and compressed product then placed in 'a furnace, such as a molybdenum wound tubefurnace, and heated in an atmosphere such as stated above, preferably hydrogen or argon. Thelshapedmassisfirst heated up to about'600fC. slowly; to allow the organicbinder to be volatilized toavoid introducing porosity into the compressed product. Thereafter, the" temperature may be raised relativelyrapidly. At temperatures below about'1300'C., incompletely sintered products are sometimes obtained; and at temperatures exceeding about 1450 C., melting of the titanium disilicide products occurs. Thus, while a sintering temperature in the range of aboutl300 to 2000 Crmay be used, optimum sintering'temperatures for. titanium disilicide are in the range of 13 50 to 1450 C., and lower silicide's are preferably heated inthe range of 1800 to 2000 C. The sintering time may range from about 0.25 to 2 :hours,

.but 0.5 to 1 hour is optimum time for silicide withbinder,

and l to 1.5 hoursforsilicide without binder.

The outstanding characteristics of the presentiinvention; as pointed out above, is that dense bodiesjmaybe formed by shaping with great'pressure of the order of and more homogeneous distribuinvention.

phere furnace maintained for titaniumtdisilicide at a temperature inthe range of about l350 to 1450 C., preferably about 1425 C., and where increasing quantities of Ti Si are present, at a temperature in the range of 1600? C. to 2000 C., holding-it there for, a time period .of A1 to 2 hours, preferably about 1 to l /z hours. Shaped bodies made with binder, as described above, of titanium disilicideiexhibit a cross-break strength of about 30,000 to 40,000 pounds per square inch,"a Rockwell A hardness of about 75 to 85, a density of about 4.0 grams per cc.', and an oxidation resistance in air at temperatures. up to about 1400 C.

The following examples illustrate the practice of this Example 1 Technically pure, finely divided titanium hydride and silicon powders in a particle size of less than about 200 mesh. are homogeneously mixed in proportions of 54 parts ,of'silicon to 46 parts of titanium by weight and heated in an ordinary tube furnace while passing dry;

oxygen-free hydrogen therethrou gh at a temperature of 1300-C.,.p1us or minus 50 C., for a period of minutes.'The reaction product, comprising substantially =titanium disilicide with less than about 5% of higher and lowIer silicides of titanium, has an ultimate density of 4.13 grams per cc. The titanium disilicide thus formed is crushed in a mill to pass a screen of about 325 mesh. The' titanium disilicide powder is then ball milled to an average particle size of 1 micron, plus or minus 0.2 mi- 7 cron.

5 to 60 tons per squarein ch -particlesof;titanium sili- Cities in a critical particle size range'of 0.5 to;5 microns,

a ou 1 m cronr u or r i u 0:2 m c gn Particles of these silicides in this, si 2e ;;ra r1 ge; are;,sg; fine,

. er, after The titanium" disilicide powder, in proportion of 500 grams, is Wet with a solution of 5 grams of Glyptal resin (the reaction product of phthalic anhydride with glycerine) dissolved in 50 cc. of acetone. The acetone is then evaporated, and the mass powdered and placed in a press having a die to shape the powder into inch square by 6 inch long bars, and shaped therein'under a forming pressure (if-20' tons' per square inch. The green, temporarily bonded bars are thenplaced in a molybdenum woundtube furnace; and dry-hydrogen gaswhich has been freedlof re's'idual'traces of oxygenis'passed therethrough, and heating begun to slowly raise the temperature. The-temperature is raised over a period of-15 minutes. to 600 C to volatilize and/ or decomposethe bindwhich the heat is raised relatively rapidly to 1500 C.'a nd held at that temperature for a-total heating period including the preliminary heating of approximatelyl hour. The titanium disilicide bars thus formed are found to have a cross-break strength of 30,000 to 35,000

V pounds per square inch, aRockwell A hardness of '75 ja at p ati e 9 ar g ii a i 4 0 silicon powders in an average particle size of about 200 mesh are homogeneously mixed in proportions of 26 parts of silicon and 74 parts of titanium by weight, then heated in an ordinary tube furnace while dry, oxygenfree hydrogen is passed therethrough at a temperature of 1400 0., plus or minus 50 C., for a period of 50 minutes. The reaction product, comprising substantially Ti Si with less than 5% of higher and lower silicides of titanium, has an ultimate density of 4.32 grams per cc. The titanium silicide thus formed is crushed in a mill to pass a screen of about 325 mesh. The powder is then ball milled to an average particle size of 1 micron, plus or minus 0.2 micron.

The titanium silicide powder, in proportion of 500 grams, is wet with a solution of 5 grams of Glyptal resin (the reaction product of phthalic anhydride with glycerine) dissolved in 50 cc. of acetone. The acetone is then evaporated and the mass powdered and placed in a press of a die to shape, the powder into /1 inch square by -6 inch long bars, and shaped therein under a forming pressure of 20 tons per square inch. The green, temporarily bonded bars are then placed in a molybdenum wound tube furnace, dry hydrogen gas which has been freed of residual traces of oxygen is passed therethrough, and heating is begun to slowly raise the temperature. The temperature is raised over a period of 15 minutes to 600 C. to stabilize and/or decompose the binder, after which the heat is raised relatively rapidly to 1800 C. and held at that temperature for a total heating period of approximately 70 minutes. The Ti Si bars thus formed were found to have a cross-break strength of approximately 35,000 pounds per square inch, a Rockwell A hardness of 78 to 82, and a density of approximately 3.85 grams per cc. The bars when heated in air are found to be resistant to oxidation at temperatures up to 2000 C.

Example 3 bars formed therefrom are substantially the same as the bars of Example 1.

- Example 4 The titanium silicide powder, formed as in Example 2 and ball milled to an average particle size of about 0.8 micron, is compressed to circular pellets in a die without a binder under a forming pressure of 45 tons per square inch, the pellets'formed having a dimension of approximately 1 inch thick by 1 inch in diameter. The pellets are carefully placed in a tube furnace and heated (without preheating) to a temperature of 1850 C. for a period of 1.5 hours. The pellets are found to have physical properties very similar to those of the bars of Example 2.

We claim:

1. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon, the silicon being in the proportion of about 26% to 64% of a the composition, to an average particle size in the range of 0.5 to 5 microns, compressing said particles under a pressure exceeding about 5 tons per square inch to temporarily bond the same into desirably shaped form, and sintering said form in a non-oxidizing atmosphere at a temperature of from about 1300 C. to about 2000 C.

2. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon,-the silicon being in the proportion of about 26% to 64%",of the composition, to an average particle size of 0.5 to 1.0 micron, compressing said particles under a pressure of about 2-0 to 60 tons per square inch, and sintering said shaped form in a non-oxidizing, noncarbonaceous atmosphere at a temperature of about 1300 to 2000 C. for about A to 2 hours.

3. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling titanium disilicide to an average particle size of 0.5 to 1.0 micron, compressing said particles under a'pressure of about 20 to 60 tons per square inch, and sintering said shaped form in a non-oxidizing, non-carbonaceous atmos-- phere at a temperature of about 1350 to 1450 C. for about to 2 hours.

4. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling titanum disilicide to an average particle size of 0.5 to 1.0 micron, compressing said particles under a pressure of about 20 to 60 tons per square inch to temporarily bond the same into a shaped form, and sintering said shaped form in a hydrogen atmosphere at a temperature of about 1425 C. for about 1 hour. 7

5. The method of forming an article of manufacture of .dense, non-porous refractory character resistant to oxida tion in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon the silicon being in the proportion of about 26 to 64% of the composition, to an average particle size in the range of 0.5 to 5 microns, forming a homogeneous blend of said particles with a temporary thermoplastic binder substance which volatilizes and decomposes leaving substantially no carbonaceous residue at the sintering temperature, compressing the powdered mix under a pressure exceeding 5 tons per square inch to form a temporarily bonded shaped form thereof, and sintering said form in a non-oxidizing atmosphere at a temperature in the range of 1300 to 2000 C.

6. The method of forming an article of manufacture of dense, nonaporous refractory character resistant to oxidation in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon, the silicon being in the proportion of about 26% to 64% of the composition, to an average particle size in the range of 0.5 to 5 microns, forming a homogeneous blend of said particles with a temporary thermoplastic binder substance which volatilizes and decomposes leaving substantially no carbonaceous residue at the sintering temperature, applied by wetting the milled powder with a solution of said binder substance in an organic solvent and evaporating the solvent, compressing the powdered mix under a pressure exceeding about 5 tons per square inch to form a temporarily bonded shaped form thereof, and sintering said form in a non-oxidizing atmosphere at a temperature in the range of 1300 to 2000 C.

I 7. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon, the silicon being in the proportion of about 26% to 64% of the composition, to an average particle size in the range of 0.5 to 5 microns, forming a homogeneous blend of said particles with a temporary alkyd resin binder, compressing the powdered mix under a pressure exceeding about 5 tons per square inch to form a temporarily bonded shaped form thereof, and sintering said form in a non-oxidizing atmosphere at a temperature in the range of 1300 to 8. The method of forming an article of manufacture of dense, non-porous refractory character resistant to oxidation in air at high temperatures, comprising milling an intermetallic composition of titanium and silicon, the

wa es;

{o -1n thereof; and sintering 'said form a non-oxidizing a mosphere at a temperature in the rangeof 1 3 to 2000 C. 1 p

9. The method of forming an article of manufacture of denseQnon-porous refractory character" resistant to oxidation in airat high temperatures, comprising milling an intermetallic composition of titanium and silicon, the siliconbeing in the proportion of about 2 6% to 64% of the composition, to an average particle size in the range of 0,3 to microns, forming a homogeneous blend of said particles with a temporary resm binder being the reaction product of phthalic anhydride with glycerine, said binder being applied by wetting the powder with a solution of said resin n a solvent and evaporating the solvent,

compressing the powdered mix under a pressure exceeding about 5 tons per square inch to form a temporarily bonded shaped form thereof, and sinteringsaid form in a non-oxidizing atmosphere at a temperature in the range of 130'0 to 2000"..C. i

10. The method of forming an article of manufacture of dense, hard, non-porous refractory character resistant to oxidation in air at high temperatures, comprising mill- 5 waxes adapted to volatilize and decompose without leavg ing any "substantial carbonaceous "residue'fat thefsiritei'ing temperature, compressing 'saidpowder and' binder under a pressure inth'e-range 'of about 5 to 40 tons'per square inch to desirably shaped form, and sintering said 10 form inanon-oxidizing atmosphere at a temperature in the ranged-130,0 to 18QQ ,Cr V

References Cited in'the file of this patent V UNITED STATES PATENTS r 1,355,994 i'Schnebel Apr. 26, 193 1,996,220 I Tigerschoid Apr. 2, 1935 2,036,245 Walter Apr. 7, 1936 2,116,399 Marth May 3', 1938 20 2,116,400' Marth l May 3, 1938 2,193,413 Wright Mar. 12, 1940 2,593,943 Wainer Apr. 22, 1952 OTHER REFERENCES 1 Alexander: Metals and Alloys, pages 179-180, July 1938. r 1

ing titanium disilicide to an average particlepsize of 1 a a 1 M m c ampm cfi vfm x said a so idorganic' binder substance selected from the' g'roiip 'consisting of thermoplastic resinsand Metallurgical Advisory Committee on Titanium Information Bulletin No. 14, March 1952. Publ. by Watertow'n Arsenal, Watertown, M as's., pages 55, 56.

Claims (1)

1. THE METHOD OF FORMING AN ARTICLE OF MANUFACTURE OF DENSE, NON-POROUS REFRACTORY CHARACTER RESISTANT TO OXIDATION IN AIR AT HIGH TEMPERATURES, COMPRISING MILLING AN INTERMETALLIC COMPOSITION OF TITANIUM AND SILICON, THE SILICON BEING IN THE PROPORTION OF ABOUT 26% TO 64% OF THE COMPOSITION, TO AN AVERAGE PARTICLE SIZE IN THE RANGE OF 0.5 TO 5 MICRONS, COMPRESSING SAID PARTICLES UNDER A PRESSURE EXCEEDING ABOUT 5 TONS PER SQUARE INCH TO TEMPORARILY BOND THE SAME INTO SESIRABLY SHAPED FORM, AND SINTERING SAID FORM IN A NON-OXIDIZING ATMOSPHERE AT A TEMPERATURE OF FROM ABOUT 1300* C. TO ABOUT 200* C.