United States PatC?f 2 ‘_ forms a new lattice structure. This isshown by X-ray' 2,982,619 di?raction tests which show the disilicide pattern present, " and silica. .When the reaction is run’ in a vacuum or a NIETALLIC COMPOUNDS FOR USE IN HIGH reducing or: inert atmosphere, the excess silicon appears TEMPERATURE APPLICATIONS ' as silicon and not as silica. . I , Roger A. Long, Bay Village, Ohio This inventor has produced the disilicide (1782 Knoxville St., San Diego, Calif.) in powdered form for use in molding various articles by No Drawing. Continuation of application Ser. No. the di?erent methods of powder metallurgy. He ob . 177,548, Aug. 3, 1950.v This application Apr. 12, 1957, tained the disilicide in powdered form by mixing‘ one 10 equivalent of _ powdered molybdenum with two mols; Ser. No. 652,358 ' ~ . equivalents of powdered silicon (325 mesh size), thor _ .8 Claims. (Cl. 23-204) oughly mixing this mixture as in a ball mill, removing the mixture from the ball mill and heatingv the stoichiomet; ‘(Granted under Title 35, US. Code (1952), sec. 266) rically proportioned ?ne mixture in air, vacuum or inert‘, This invention relates to metallic compounds which 15 gas atmosphere until an exothermic reaction occurred’; are characterized by a relatively high , i.e. A suitable v'essel‘of refractory material, such as a crucible‘ relatively high refractoriness, and by resistance to oxida ' or boat of alundum, beryllia, etc., may be used for hold tion and abrasion at elevated temperatures. In particu~~ ing the powder mixture which is produced in the 'furnac'eQ This reaction took place at about l900° F.:L100° F. with lar the invention relates to inter-metallic compounds of 20 silicon with certain metals of the fourth and’ sixth groups a subsequent temperature rise to about. 3000° F. The of the periodic table of the elements. More-speci?cally powder was then crushed, ball-milled and leached withd the invention relates to an inter-metallic compound of ' concentrated ‘to remove any unreacted molyb molybdenum di-silicide and to its properties and uses. denum metal and with hot hydrochloric acid to remove any molybdenum oxide. Leaching is not necessary“ The general object of the invention is to produce an 25 inter-metallic compound or an intermediate solid solu when reacting in a vacuum or gas atmosphere. It was tion of silicon and a metal selected from the group con found that the silicon volatilized at the reaction tem1 " sisting of uranium, molybdenum, chromium, tungsten, ‘ perature under a vacuum; that it was necessary to carry? zirconium, and titanium by a novel method of heat. the reaction to completion in a partial pressure atmos- phere of argon or helium when such gas was introduced treatment. / 30 It is a further object of the invention 'to produce an into the vacuum to furnish up to one half to three inter-metallic compound of silicon with one of the above . quarters atmospheric pressure. de?ned metals which is relatively refractory and resistant The molybdenum disilicide produced by this method‘ ‘to abrasion at high temperatures. ' was not fused; it was friable and was readily ground to a It is a particular object of the invention to produce an desired ?neness by/ball-milling or other particle reduc inter-metallic compound of silicon and molybdenum in ing methods. This grinding will be described herein which these components are combined in the stoichio after. 1 ' metric proportions of molybdenum di-silicide (Mosiz). vIt was also discovered that a mass of high-purity pow It is an additional object of the invention to produce der of molybdenum disilicide (Mosiz), ?ne particles; a di-silicide of molybdenum which by methods of pow without addition of any generally used binder substances, der metallurgy may be molded and shaped into products such as, cobalt, nickel, or the like, will when compacted that are resistant to oxidation, are of accurate dimensions under pressure and heat by known powder metallurgical and relatively high mechanical strength. ' techniques yield a cemented body of substantially pure An object also is to provide a composition formed by molybdenum disilicide (Mosiz) exhibiting extremely de a mixture of a di-silicide of a metal selected from the 45 sirable hot, physical and mechanical properties, which group consisting of uranium, molybdenum, chromium, combined with its ‘superior corrosion resistance makes it tungsten, zirconium, and titanium, with other metals, ideal for applications such as gas-turbine buckets, ?ame semi-metals, oxides, carbides, borides or other silicides. holders and the like. \ ‘_ - V An additional object of the invention is to produce a This inventor produced the disilicides of metals other~ than molybdenum by this direct reaction method. In compound of silicon having high corrosion and wear 50 resistant properties. . particular he produced the disilicides of uranium, chro Prior scienti?c and patent literature contains various mium, tungsten, zirconium, and titanium. These silicides suggestions for the production of molybdenum disilicide. vary from one to the other in their physical properties However as far as the inventor is aware, there was not and construction. They vary in refractoriness and in re- ' sistance to oxidation at high temperature. But all are available up to the present time a simple process for 55 producing molybdenum disilicide of relatively high purity useful in certain applications. in a form in which it could be readily comminuted into A second method of powdered metal preparation in ?ne particles for use in producing by powder-metallurgy which powdered molybdenum disilicide, prepared as i technique shaped cemented bodies of great hot strength above described, is impregnated with other metals such as copper, nickel, cobalt, etc. or other alloys, such as and corrosion resistance. . 60 The present invention is based on the discovery that, “Colomonoy No. 6,” Phosphor bronze, etc. In. this‘ when a stoichiometrically proportioned intimate mixture method of preparation these additive metals and alloys of ?ne particles of molybdenum and silicon, correspond are drawn into the'skeleton of the molybdenum disilicide ' ing to the formula Mdsiz, is heated to an elevated tem to form’ an intimate material. These alloys are not as ‘ refractory as the molybdenum disilicide alone, but they perature of about 2000° R, which is well below the melt 65 ing point of these components, a reaction takes place are useful for the reason that they can be readily worked between them which results in the production of rela ‘by the process of “hot forming” i.e. “hot coining.” Y . tively pure molybdenum disilicide in a friable form which These disilicides may be considered ‘as being inter may be readily comminuted into ?ne powder particles metallic compounds or metal compound phases. Broadly ' they are intermediate solid solutions some of which have ' suitable for powder metallurgy processing. The reaction 70 of the silicon with the molybdenum is exothermic and wide and others narrow ranges of homogeneity. ‘Since 1 the .temperaturerises to about 3000“ F. Thesilicon re true intermetallic compounds have narrow rangesmof ho acts with the molybdenum throughout the mass and 5 mogeneity and simple stoichiometric- proportions with i a aesae 1e 3 4 atoms of identical kinds occupying identical points on the ' (3) Vacuum casting. lattice, all of the disilides of this invention cannot be (4) ‘Hot coining. classed as true intermetallic compounds. They are all (5) Swaging and rolling. intermediate solid solutions and some of them, for ex The formed material canbe machined and brazed to ample,‘ USi-é, WSig, TiSi2, CrSi2, and ZrSi2 may be, of the ?nal required forms by methods such as: , either type, particularly ZrSiz and TiSiz which apparently (1) Grinding, diamond or gravity fed have wide range of homogeneity and can contain excessive wheel. V ‘ silicon and/or excessive zirconium in solution with the (2) Machining, using‘ carbide tools (only when in a disilicide. ‘ partially sintered condition). But in the case of titanium disilicide, the theoretical 10 ( 3) Brazing, using silver, copper or colomonoy alloys. analysis of which is: ' PRODUCTION OF ARTICLES BY THE METHODS Titanium ~ ______46.05 OF POWDER METALLURGY 7 Silicon ___ 53.95 As stated above, the production of articles ‘by the methods of powder metallurgy can be accomplished by 100.00 ?ne basic methods. The V?rst of these, cold press and the analyses of powdered silicides, prepared as above sinter, because of its extensive use industrially will be described gave the following: discussed ?rst. The cold press and sinter method I II 20 This method is now used commercially in the fabrica Titanium;...... _. 49. 0 44. to tion of cemented carbides. This method, with some modi Silicon. - . ____ _- 47. 3 50. 30 ?cation, can be used for the making of articles from the Iron 1. 04 Aluminum--. _ . . 95 powdered disilicides of this invention and particularly for Other Impurities ...... __ 3. 7 3. 60 25 the molding of powdered molybdenum disilicide. 100. 00 100. 00 In this process cold pressing is accomplished by the use of properly shaped permanent dies and applied pres In neither case are the titanium and silicon present in sure. The dies are oversized to allow for shrinkage dur the theoretical proportions. Thesecompounds, however, ing . The pressure used varies with the shape showed goodqresults at elevated temperatures and must be 30 of the work, the organic binder used, and the compacting considered only as intermediate solid solutions. necessary for good, green, mechanical strength. The pres , as produced by the method of this sure must be uniformly applied over thcentire die in inventor is a true intermetallic compound, checking very order to increase the resistance to possible later thermal close to stoichiometric proportions. For some reason, shock. ' The pressures used vary between about ten and not at present known, this compound although highly re thirty tons per square inch. After the, compacted piece fractory, is not as resistant tooxidation as the other above is removed from the press it is sintered at a, relatively high listed disilicides. Its use is therefore limited to high tem temperature about 2700° F.~3l00° F. either in a vac perature operations where oxidizing conditions are not too uum or ‘an inert atmosphere'such as argon or helium. severe. This inventor found that hydrogen, although widely used The use of these powdered disilicides is extensive. They 4.0 in commercial processes of sintering cemented carbides, may be used as a protective coating on other metal bases. cannot generally be used without some dif?culties with to inhibit oxidation of such bases at elevated temperatures, pure molybdenum disilicide bodies; but that hydrogen or they may be used as metallic powders either ‘alone or could be used as a reducing atmosphere in the ‘sintering alloyed with other metals or semi-metals to form articles‘ step if small additions of binder metals, such‘ as nickel of simple or relatively complicated shape by the methods 45 and cobalt,’ were ‘made to the powdered disilicide. The of powder metallurgy. use of a hydrogen atmosphere is very desirable because As a protective coating on other metallic bases, molyb~ of the relatively low cost‘ and its commercial use. The use‘ of binder metals such as nickel and cobalt denum disilicide may preferably be applied in one of three permits hydrogen sintering atmospheres and sintering ways: . (1) As a coating on molybdenum, silicon is applied as 50 temperatures up to about 2600° F. ‘ Above this tempera a coating on a piece of molybdenum, the coated piece is ture cracking occurs. The addition of iron or chromium then heated to a temperature at which ‘diffusion occurs, as a binder metal lowers the sintering temperature to and the silicon diffuses into the molybdenum thereby about 2430” F., above which temperature cracking occurs. forming a strong bond for the coatingto the base metal. Particle size of the disilicide powder is important in the (2) The application of a disilicide of one of the metals cold press and sinter method for. the effect it has on the of the above de?ned group, for instance, molybdenum density and mechanical strength of the sintered body. disilicide as a protective coating on the surface of a base While not, as yet, completely determined, test data indi material. The coating is applied by spraying the pow cate that a particle size of from one to about six microns dered silicide by means of a powdered metal spray gun is desirable. in an atmosphere of helium, argon, nitrogen, or hydrogen 60 The cold press and sinter method includes the con under a pressure of from ?ve to eight atmospheres and ventional processes of extrusion and slip-casting. In subsequently di?using the disilicide into the base material the extrusion process a powder extrusion gun is used. in an inert gas atmosphere or vacuum. The powder (the disilicide), after being mixed with or (3) The disilicide is worked up in a carrier medium ganic binders, such as starch, glycerine, waxes, etc. is and applied as a brush coat on the surface of the base extruded through speci?c dies. The extruded parts are metal. The coated metal is then baked at a high tem then slowly heated from low temperatures to maximum perature, in an inert atmosphere or vacuum to diffuse the sintering temperatures. This process is particularly ap disilicide into the surface of the base metal thereby form plicable in the fabrication of tubes. The slip-casting ing a strong bond for. the disilicide coating. process may be used for making odd and complicated .The fabrication of the powdered disilicides of the group 70 shapes and forms of these disilicides. A slurry is made ofmetals above de?ned, and of molybdenum in particular, with organic binders and cast into mold, after drying can be accomplished by a number of methods for example the shape is sintered slowly as in the extrusion process. as follows: (l). Cold. pressing and sintering. The hot press method .(2) Harnessing. > . 75 ‘The disilicides 0t themetals abcve de?ned may ‘also 2,982,619 5 6 be molded and shaped inipowdered form by‘ the “hot press ,, "b'. A- greater hot press pressure-anda higher hot press‘

method.” In particular‘ molybdenum disilicide, *which. temperatureor I , ‘ 1" " ‘ " ‘ may be prepared with a purity of about 99.8%, may be c. Acombination of both. molded by this method. For successful use in this The low limit of density may be attained by: method of pressing, the powder must be ground to a _ a. A very uniform ?ne particle size (100 percent less ?ne state of subdivision. This reduction in particle size than 6 microns inpdiameter with 90 percent less than 3 is preferably accomplished by wet ball milling of the microns) . powder in an alcohol or acctone'medium for control. ' b. A lower hot press pressure and a lower hot press‘

This inventor has found that if maximum high-tem . temperature or, _ . . . . . perature properties are desired, the particle size of the 10 a c. A combination of both. ‘ powdered disilicide for hot pressing and probably for Reference to Table _2 shows that the density of the the other methods herein described, should be as follows: 'molybdenum disilcide can‘ be‘ varied by merely varying ' the particle size and the particle size distribution and that ' TABLE I 4 V V 'with a decrease in density?dueto. an increase in ,?neness , Percent of of particle size and a more uniform particle size distri Particle Size Total bution there is a drop inf theful'tim'ate breaking strengthv at the same temperature. " 0-6 microns. 90 400 6-26 microns- 0-10 The above described hot-press'procedures'have' been used for making various fabricated parts, such as ?ame 20 holder plates, turbine blades'and bars. Test data indicates that as regards to strength at least 90 percent of the particles must be less than 6 microns 7 Vacuum casting in diameter. It has not been possible to produce porosity-‘free bars The powder upon removal from the ball mill must be of molybdenum disilicide by this method. Experimental 25 completely dried and when necessary leached with dilute tests, however, indicate that this disilicide can be cast hydrochloric acid to remove metallic iron which may in a positive pressure atmosphere of an inert gas, i.e. have been picked up during ball milling. argon or helium. The powder is then pressed to the shape desired by It was found that zircon crucibles could be used satis- , " the use of graphite form molds. The temperature used factorily for the melting and that in connection with for hot pressing may vary between 2600° F. and 3100" 30 porosity developed in bars cast in vacuo this leads to F. Because of commercial limitations it is more practi gas entrapment in the body of the casting; that hot press cable to use temperatures within the range of 2700" F. slugs also contain a considerable quantity of entrapped to3000°F. ' ' . ' - ' ’ gas and that in powdered cold-press and vacuum sintered The pressure used for hot pressing may be varied gen 35 slugs the largest part of entrapped gas‘ is eliminated. erally from 500 to ‘7000 pounds per square inch depend In its present state of development the vacuum cast ing upon the strength of the graphite dies and‘ the tem ing process is believed to be too costly for extensive use. perature used for pressing.v The relative brittleness of the disilicide, however, increases with increase in the Hot coining applied pressure to the maximum allowable with the graphite dies. It is therefore more desirable’ to use . 40. This method of fabrication is a ?nishing process which pressures near the mean of the pressure limits for reasons from an economical standpoint is highly advantageous. of costas well as less brittleness. The density of the It is similar to hot pressingan already particularly sin disilicide also generally increases with the pressure and tered part. A part could therefore be cold-pressed and partly sintered to shape and then hot forged or hot a pressure of from 1000 to 2000 pounds per square inch coined to the ?nal exact shape. This operation accom is required to obtain a density of over 5.0 grams per 45 plishes densi?cation, dimensional stability and eliminates cubic centimeter when using ?ne powder (90% less or minimizes ?nish machining operations. than 6 microns). Prolonged soaking at the temperature of hot pressing 7 Swaging and rolling increases slightly the shock resistance or toughness of the disilicide at room temperature. Pressing and soaking at 50 These fabrication processes are also ?nishing opera temperatures'of 2900°-3200° F. have a greater elfect on tions. Material made into by the extrusion, cold-press shock resistance or toughness of pieces than on samples and sinter or hot-press ‘methods might be hot swaged or pressed and soaked at lower pressing temperatures. Ap hot rolled above the brittle range of the ductile disilicide, parently the pressing temperature is the effective variable viz. under the following physical conditions: _ in the control of this physical characteristic. 7 55 a. Fineness-100 percent less than 6 microns in diarn~ The fractured disilicide, when hot pressed under th eter, 90 percent less than 3 microns in diameter and at an optimum conditions of temperature, pressure, particle size b. Approximate temperature range-from 2600 to and particle size distribution, has a ?ne grained; silky, 3100° F. for rods, wire, or plates. satiny luster similar to that obtained when hot-pressed The following requirements. for effective swaging and ’ cemented tungsten carbide is fractured. I Q ' ' ' V 60 rolling have been experimentally determined: The density of the hot pressed molybdenum disilicide ayHigh purity of material is required, otherwise, the may be varied over the range of from 5.00 to ‘about 6.15 material is hot short‘. and cracking occurs. grams per cubic centimeter by 'variation in the follow? b. Fine uniform particle size is required (100 percent - ing physical characteristics of the components and factors less than 3 microns. in diameter). in the method of pressing: 65 0. Swaging temperature preferably should be in excess ‘ a. Particle size. ‘ ' of 2800° F., but not greater than 3100° F. ' b. Particle size distribution. d. Percent reduction should be at a slow rate initially. .c. Pressure. - > I MECHANICAL‘PROPERTIES AT ROOM AND ELE d. Temperature of hot pressing. ' ' VATED TEMPERATURES ' OF HOT-PRESSED. The density for maximum strength properties varied 70 between 5.80 and 6.15 grams per cubic centimeter with MOLYBDENUM DISILICIDEv I 5.80 to 5.95 being the more desirable density ?gure. The I In the followingtable are given test data on the high density limit may be attained by: , > change in ultimate breaking strength from that at room ' a. A ?ne particle size'rwith non-uniform particle size‘ temperature to that at 1800°, 2000°, 2200", and 2400° at distribution.v , j , ., . " . . . . 75 vF. on rods of molybdenum disilicide which were formed 2,98%619“ 22 I or by‘ the hot-press method and which varied ‘in particle must be noted, however,» that increase in ductility . is size and particle size distribution ‘as indicated. accompanied by a decrease in high temperature strength,

TABLE 2

Total elonga- - Particle Size (Microscopic Count). Density, Purity, Test Tempera tion Percent . g./cc. Percent ture, cl— in 3"

Room Temp" Not Detect 100%<15 microns, 5c%<5 microns ...... able. __ Do.

Do: 0.1 percent. 0.5 percent.

1 Broke in grip collet. . 9 Pulled through the ‘high temperature grips. No'rn.~The increase in elevated temperature tensile strength from the strength at room temperature is due to better alignment and fit of all grip material and specimen at the elevated temperatures. It could also be due to an increase in the disiliclde ductility as the temperature increased (this ductility could be vcr% little and not detectable by ordinary measuring methods). It is also possible that this increase is due to a di usion process in the disilicide at elevated temperatures. Tests are ncwlln progress to ascertain whether or not this is true.

The decrease in density with increase of uniformly and that ductility at room temperature cannot be de distributed and decreased range in particle size is noted. tected. . The increase in ultimate breaking strength from that at ' THERMAL EXPANSION room temperature to that at elevated temperatures is Determination of the cumulative thermal expansion of relatively great. This may be due to several causes triangular prisms of molybdenum disilicide was made of none of which is the inventor certain. This increase through the temperature range ‘of room temperature to may be due to: 40 1500° C. followed by a reverse determination of from a. Better alignment and ?t of all grip material and 1500“ C. to room temperature. The‘particle size of the the‘specimen. sample is as shown in Table 1. The density of the sam b. An increase in ductility of the disilicide. ple was 5.93 to 5.94 grams per cubic centimeter. The In other words this table shows generally that: test results are given in Table 3. As the particle size decreases, TABLE 3.———LINEAR THERMAL EXPANSION a. The elevated temperature breaking strength in ‘ CUMULATIVE PERCENT

creases. ' b. The ductility increases. During Heating During Cooling 0. The density decreases slightly. As the ‘particle size distribution becomes more uni 60 ° 0. Percent ° 0. Percent form, 0.00 1. 35 a. The elevated temperature breaking strength de . 04 1. 21 creases attcmperatnres at and above 2200° F. ‘ . 12 1. 09 .20 . 97 . b. The ductility at elevated temperatures increases. .29 .86 c. The density tends to decrease slightly for similar . 38 . 75 . 47 . 65 pressing conditions. 7 v . 56 . 5G In general it may be concluded from the data in Table . 65 .46 . 74 . 38 2 that: . 85 .29 . 95 .20 a. The ultimate breaking strength of the material re 1. 06 .12 mains approximately constant from room temperature 1. 16 . [l5 1. 26 —~. 02 to 2400° F. provided that the particle size and particle 1. 36 —. 0S size distribution are as that shown in Table .1. b. The ductility of the material increases at elevated temperatures provided that particle size and particle size It is noted that the material had a linear shrinkage 65 of .08 percent upon cooling to room temperature. This ‘ distribution are as shown in line 1, Table 1. is due to an additional sintering action occasioned by the c. The ultimate breaking strength of they material de heating to 1500° C. ‘ creases above 2200“ F. and the ductility increases pro vided the particle size is 100 percent less than 6 microns AIR CORROSION PROPERTIES ' and uniform in distribution (90 percent to 95 percen 70 This inventor has found that molybdenum disilicide less than 3 microns in diameter). ' is very resistant to corrosion, i.e. oxidation in air at elc- ' ,.Ductility is an importantcharacteristicin‘many appli vated temperatures. Pieces of this disilicide of‘known cations and uses of this material. This is‘the property area were held in a furnace, in an atmosphere of air,, which decreases ‘the “notc ‘” sensitivity, relieves initial at ‘temperatures of 2200°, F., 2450° F., and 2850" F., thermal‘ stresses, and facilitates commercial handling. 75 for 100 hour, 200 hour, and 300 hour periods. of time. _‘ 2,982,619 9 I‘ 10 The pieces were then cooled and the gain or loss in .. . is one of the most important problems relating to molyb weight was determined. The results are given inrthe fol , denum disilicide], lowing table: . .The basic reason for these metallic additions‘ is to'inH-W 7' crease the toughness or decrease the inherent brittleness TABLE 4.-—AIR CORROSION DATA 5 of the intermetallic compound. - > » ' - ' ~~ Preliminary tests showed that iron, nickel, cobalt, chro-' Rate gm. em! hr. ' Eninrn, and platinum “wetted’ithe molybdenum disilicide, Temperature, ° F. ' I n V therebyindicating de?nite possibilitieslfo'r ‘good alloying 100 hours 200 hours 300 hours ‘ "toughening characteristics. ~' ' ' 10 ' Oxidation tests indicated that for temperatures uplto' 0. esxm-n 1. o><1o-a ' 0. 7x10-H 3. 0X10‘0 0. 96-10"l 0. 64Xl0-ll 7:2600" F. an alloying content up to 20 percent of cobalt 3. 67X10'° a 3. 1X10’" _-__-_-_----.- .....was possible without too great a deterioration. The rela ,tive toughness comparison of 5, 10, and 20 percent addi 1 Weight gain. I’ tions of cobalt indicated that the 5 or. '10-‘.percent addi 3 Weight loss. tion was better than that of the 20 percent. Also short 8 Time-135 hrs. time oxidation tests at 2800" F. showed that the addition. Examination of this table indicates that there is very ‘of 5v to 10 percent of cobalt did not affectithe resistance ' little effect of air corrosion on the molybdenum disilicide: to oxidation properties appreciably. at elevated temperatures. It is noted that at the lower“ Investigations were therefore conducted‘- on the basis temperatures (below 2500° F.) there is a weight gain, of using from 7 to 8 percent metallic additions of co-"‘ while ‘after heating ‘at the higher temperature there is balt, nickel and platinum. The ?ne molybednum di aY‘Weight loss; This is due to7 the movement of a sec-. silicide powder was ball-milled in benzeneand/ or alcohol ondary impurity phase to the surface and the burning or acetone with these metallic additions for seventy two or volatilizing away of portions of this phase as it reaches hours and dried. Bars of the material were hot pressed the surface. . 25 at temperatures above the melting points of the alloying - Electron diffraction photographs of the surface before. metals. Dl?‘iculty was encountered with the cobalt addi and‘after heating has shown the presence of an amor tion and many of the bars containing this additivewere phous phase on the ‘surface after heating at 28500 F. cracked after the graphite die hadvcooled. The nickel , This can be removed by slight polishing and the crystal and platinum bars did not crack and manufacturing con~ line pattern of molybdenum disilicide surface returns. 30 ,ditions indicated that the nickel addition was best 'for' Metallographic analysis shows the loss of the secondary handling. The 7.5 percent nickel bars were machined‘ phase to the surface from the interior, which substan into tensile strength specimens and weretested at 2000" ' tiates the electron di?raction and corrosion results. F. The results showed an ultimate strength of only The minute secondary phase thus accounts for the 4,000 pounds per square inch, as compared to 40,000 change in weight upon heating in the tests conducted. 35 pounds per square inch for the straight molybdenumv It is believed that by the‘elimination of this phase,‘the silicide. The reason for this relatively large reduction air corrosion resistance properties will be, much betterv in ultimate strength at 2000° F. is being investigated by than that shown and that the physical properties will metallographic and X-ray analysis. also be improved. ' ' ' ' The use of alloy additions for the cold press ‘and 40 sintering process was discussed supra. As a result of, I CHEMICALVCORRODIBILlTY the above tests it was decided that the alloy addition' - At normal temperatures molybdenum disilicide is rela should be reduced to the range of from l'to 4 percent‘ tively inert or non-reactive to acid‘ or basic re-agents. for maximum tensile strength. Thus in Table 6 is shown Table 5 shows the percentage loss in weight per hour the variation in ultimate tensile breaking strength of of thisdisilicide in reaction at 70° F. with two concen 45 molybdenum disilicide specimens each one containing ad trations of nitric acid, hydro?uoric acid, sulphuric acid, ditions of 3.3 percent by Weight of iron, ‘cobalt, nickel, hydrochloric acid and sodium. hydroxide. and chromium, respectively. These specimens were cold. _ pressed and sintered at the temperatures indicated, viz. ' .‘I‘ABLE 5.——CHEMICAL CORRODIBILITY 0F , MOLYBDENUM DISILIOIDE AT 70° F. 1250° C., 1300° C., 1350° ‘C., 1400° C., and 1450° C. in an atmosphere of hydrogen and also at 1450.0 C. in 7 [Percent change in weight per hour] 50 vacuo. It should be noted that, in general, the nickel addi-" emanation _ HNO; HF ms o. H01 NsOH tion gave the higher modulus of rupture values partic-" 10%--.‘ ...... O. 0034 0. 0019 0. 0005 00l-2 ularly for the specimens sintered at 1300° C. and 1350,0 Concentrated .... -- 0. 010 0. (1012 0. 0005 0. 0001 55 C. Also it should be noted that with a relatively small" addition of these alloying metals these results were ob tained on specimens which had been sintered in an atmos :The almost “negligible reaction of this disilicide with phere of hydrogen. This makes commercially available the ordinary re-agents is clearlyshown in the above various shapes and forms not otherwise available at table. . 60 reasonable cost. j . . .WEAR RESISTANCE Other elements Wereadded for the express purpose of ‘ The hardness of hot pressed molybdenum disilicide, cleansing the disilicide particles. of oxygen or other gases.‘ Rockwell A—80-90, equals that of many of the present These additions amounted to from 0.1 percent-2.0 per-_ ' cemented carbides. Its resistance to'wear, i.e. abrasion, cent and consisted generally of getter» elements. Ex. __ is therefore‘believed to be of the same order asthat of 65 titanium, zirconium, carbon, etc. These additions would these carbides.‘ Comparative data on this physical char tend .to increase inter-particle cohesiveness, and thus an acteristic are not yet available. The combination of the increase in the strength of the bodies was noted. resistance to abrasion'ofthis'material with its excellent NON-METALLIC ADDITIONS (l) physical strength and'resistance to corrosion, all at ele vatéd temperatures, opens up a rather extensive ?eld of The addition of small amounts of oxides, carbides,‘ 1.0 borides and other silicides on the order of from 0.1 per¢ application in its use. "_ “ r '_ ‘ . cent to 35 percent additions topthe disilicide bodies is;

’ . .. ,MEIALLIQ'ADDIIIONS practical. These additions are made .to incr'ease?the The ‘use of other metals. to form homogeneous alloys elevated temperature properties of the disilicide bodies__ or to form a f‘cementing” phase heterogeneous material 75, for specialized purposes. " ' anaemic‘ 111" 12 ‘TABLE 6.—ME’I‘ALLIO ADDITIONS-SINTERING EFFECT‘ .

. 150050. 1,35o°o. 1,400" 0. 1,450“ 0. 1,450“ O. (H2) (H2) (H2) (H2) (Vac) Iron: Trans. Strength (p.s.l.) Cracked 48. 400 Hardness (Rx) Broke. 16 .5 5.16

ShrinkageDensity ...... _

NON-METALLIC ADDITIONS (2) 4. A process for forming a sintered powder metallurgy product consisting essentially of sintered powder particles The use of molybdenum disilicide as a binder metal for selected from the group consisting of powder particles of very high‘temperature applications (30000 F. to 5000" the‘ disilicides of uranium, molybdenum, chromium, tung F.) with such compounds as beryllia, alumina, and the sten, zirconium and titanium, said process comprising metal carbides is practical. forming said disilicides in each instance by heating an Tests were run using BeO (beryilia) and A263 intimate mixture of the elements thereof in powder form (alumina). Samples containing up to 25 percent of to a temperature initially less than the melting‘tempera molybdenum disilicide were hot pressed at a temperature ture of said elements and high enough to initiate reaction above that of the disilicide. The compacts were then between said elements and allowing said reaction to pro heated in air in an induction furnace to temperatures in ceed tosubstantial completion and produce a disilicide in excess of 3800" F. Little effect was noted on the samples a friable form and thereafter milling said friable disilicides and the use of this type of “ceramal” for very high tem to said powder particles to a degree reducing them to a perature use looks promising. particle size substantially 100% less than 25 microns; and vDisclosure has been made of a preferred method of 35 forming said disilicide powder particles to the desired compounding the disilicides of certain metals of the fourth shape of said product and heating the resulting shape to and sixth groups of the periodic table. The method dis sinter said disilicide powder particles. closed does not involve the complete fusion of the base 5. A process for forming a sintered powder metallurgy metal and the silicon as is done in the prior art. In this product consisting essentially of sintered powder particles mventor’s method the silicon upon reaction with the base 40 selected from the group consisting of powder particles metal enters the lattice structure thereof forming either a of the disilicides of uranium, molybdenum, chromium, de?nite compound, an intermetallic compound or an in tungsten, zirconium and titanium, said process compris termediate solid solution therewith. Inasmuch as it is ing forming said disilicides in each instance by heating sometimes desirable to have a small excess of silicon an intimate mixture of the elements thereof in’ powder present and at other times a small excess of the group form to ‘a temperature initially‘ less than the melting tem element present, variations from the particular proper» 45 perature of said elements and high enough to initiate tions given supra can be made without departing from the reaction between said elements and allowing said reac spirit or scope of the invention beyond that ‘as de?ned by . tion to proceed to substantial completion and produce the herewith appended claims. , . The invention described herein may be manufactured a disilicide .in a friable form and thereafter milling said and used by or for the Government of the United States 50 friable disilicides to said powder particles to a degree of America for governmental purposes without the pay reducing them to a particle size substantially 100% less ment of any royalties thereon or therefor. - than 25 microns and at least.90% to a maximum par This is a continuation of application Serial No. 177,548, ticle size of 6 microns; and forming said disilicide powder ?led August 3, 1950, now abandoned. particles to the desired shape of said product and heating What is claimed is: 55 the resulting shape to sinter said disilicide powder par 1. An article of manufacture comprising a sintered ticles. powder metallurgy product consisting essentially of sin 6; A process for forming an article of manufacture tered powder particles selected from the group consisting comprising a sintered powder metallurgy product con of the disilicides of uranium, molybdenum, chromium, sisting essentially of sintered powder particles selected tungsten, zirconium and titanium powdered substantially 60 from the group consisting of powder particles of the di~ 100% to particle sizes substantially less than 25 microns. silicides of uranium, molybdenum, chromium, ‘tungsten, 2. An article of manufacture comprising a sintered zirconium and titanium, said process comprising‘forming powder metallurgy product consisting essentially of sin said disilicides in each‘ instance by heating an intimate tered powder particles selected from the group consisting mixture of‘ the elements thereof in powder form to a temperature initially less than the melting temperature of the disilicides of uranium, molybdenum, chromium, 65 tungsten, zirconium and titanium powdered substantially of said elements and high enough to initiate reaction 100% to particle sizes substantially, less than 25 microns; between said elements and allowing said reaction to pro at least 90% of said particles having a particle size less ceed to substantial completion and produce a disilicide than 6-microns; in a friable form and thereafter milling said friable di [3..An article of manufacture comprising a sintered 70 silicides to said powder‘iparticles to a degree reducing powder metallurgy product consisting essentially of sin them to a particle'size substantially 100% less than 25 tercd molybdenum disilicide powder particles powdered microns; cold pressing said disilicide powder particles to substantially 100% to a particle size less than 25 microns, form an unsintered piece having the desired shape of said‘ product having a density ranging from 5.00 to about said‘prodnct, and sintering said piece to form said product. 6.15 grams per cubic centimeter. 76 7. A process for forming an article of manufacture 2,982,619 , 13 ‘14 comprising a sintered powder metallurgy product consist st-antial completion and produce molybdenum disilicide ing essentially of sintered powder particles selected from ina friable form and thereafter milling said friable molyb the group consisting of powder particles of the disilicides denum disilicide to said powder particles to a degree re of uranium, molybdenum, chromium, tungsten, zirconi ducing them to a particle size substantially 100% less um and titanium, said process comprising forming said than 25 microns, forming said milled particles into a disilicide in each instance by heating an intimate mixture preliminary shape, heating said shape to sinter said disili of the elements thereof in‘powder form to a temperature cide powder particles, thereafter heating said shape to initially less than the melting temperature of said ele temperatures ranging from about 2600 to 3100° F. and ments and high enough to initiate reaction between said ' above the brittle temperature range of said sintered di elements and allowing said reaction to proceed to sub 10 silicide shape, and while said shape is thus heated hot stantial completion and produce a disilicide in a friable Working said shape to the i?nal desired shape of said form and thereafter milling said friable disilicides to said product. powder particles to a degree reducing them to a particle size substantially 100% less than 25 microns; placing References Cited in the ?le of this patent said disilicide powder particles in a mold and ‘applying 15 UNITED STATES PATENTS high pressure and heat to said particles in said mold so as to hot press and sinter said particles in said mold to 1,560,885 Walter ______NOV. 10, 1925 form said product to the shape of said mold. 2,089,030 Kratky ______.._ Aug. 3, 1937 8. A process for forming a sintered powder metallurgy 2,116,400 Marth ______.... May 3, 1938 product consisting essentially of sintered powder parti 20 2,193,413 Wright ______.. Mar. 12, 1940 cles of molybdenum disilicide, said process comprising 2,665,474 Beirdler ______Jan. 12, 1954 forming said disilicide by heating an intimate mixture of 2,779,580 Steinitz ______Ian. 29, 1957 the elements thereof in powder form to a temperature 2,921,861 Wehrmann et al ______Jan. 19, 1960 initially less than the melting temperature of said ele FOREIGN PATENTS ments and high enough to initiate reaction between said 25 elements and allowing said reaction to proceed to sub-, 435,754 Great Britain ______Sept. 23, 1935