US3218697A - Method of preparing fiber reinforced metals - Google Patents

Description

Nov. 23, 1965 E. WAINER 3,218,697

METHOD OF PREPARING FIBER REINFORCED METALS Filed July 20, 1962 FIG. I I FIG. 2. (Sintering) (Fusion) Form Extrudable Mixture Of: Form MixtureOt Figure l Metal Powder Omitting The Plasticizer Sapphire Fibers Extrusion Agent 0 (Plosticizer) l Oven Dry At 325 C. I

Water Solution Of Alkaline Earth Salt Break Down Dried Cake Water Solution Of t in Mortarwith Rubber Chromium Salt pesfle Extrude At Room Temperature With Area Reguction OfAt Least Pour Que": Tu be I t I insert Tube In Opening 0 Provided in insulating DryAt325 0., One Hour l Refractory Seeve Heat To Sintering Temperature ln Stream Of Hydrogen Hem 2312 133 Retain At Temperature l Hour p Maintain At Temperature I Cool in Hydrogen I For 3 Minutes Reduce Cross SectionalArea Work To Desired Final IO%- l5% By Gold Size And Shape eg Working By Rolling Or WireDrawing Reheat To Original Sintering Temperature in Flowing Hydrogen Retain At Temperature l Hour Wire-Draw, Swage Or Other Cold Work To Finished Size And Shape INVENTOR Eugene Woiner BY 0am 1 3M ATTORNEY United States Patent 3,218,697 METHOD OF PREPARING FIBER REINFORCED METALS Eugene Wainer, Shaker Heights, Ohio, assignor to Horizons Incorporated, Cleveland, Ohio, a corporation of New Jersey Filed July 20, 1962, Ser. No. 211,284 8 Claims. (Cl. 29420.5)

This invention relates to metals and alloys reinforced with high strength inorganic fibers and to methods of preparing such composite materials More particularly it relates to the production of products having physical properties and particularly mechanical properties such as tensile strengths greatly increased as compared with the properties of the same metals and alloys without reinforcement by the inorganic fibers.

The value of fibers as reinforcements to enhance the physical properties of structural materials such as plastics, ceramics and metals is known. When either the fibers or the matrix material is a metal or metal alloy, it has been found that in order to develop the full capabilities of the system of materials, the matrix and reinforcement must wet one another. Otherwise the bond formed between the two is a source of weakness and the composites fail in either tension or shear when subjected to stresses which the composite materials should be able to handle. The problem is particularly acute with metal-containing systems because at the temperatures at which the composites are generally prepared, oxidation of one or more of the metals present often interferes with the desired bond formation.

One object of this invention is to provide a process by which the full capabilities of the composite materials based on a metallic matrix reinforced with sapphire fibers or filaments are achieved.

A specific object of the invention is the production of composite materials possessed of exceptionally high strength, yet capable of being formed by conventional tools into useful structural members, e.g. by sawing, cutting, milling and similar shaping procedures.

These and other objects of the invention are realized by the preparation of fiber reinforced metal based composites consisting essentially of three constituents as follows:

(1) One or more metals or alloys in amounts up to 99% of the total weight of the composite;

(2) Filaments or wool-like fibers of alpha alumina (corundum or sapphire) comprising between about 1.5 and of the entire composite by weight and distributed in a preferred orientation throughout the composite; and

(3) A very minute amount of materials which cause the metal component (1) and the alpha alumina (2) to wet one another and to bond together without impairing the chemical or structural integrity of the alumina fibers, and consisting of specified amounts of one or more water soluble salts of an alkaline earth metal including magnesium, and a related amount of chromium either (a) as a water-soluble chromium salt, or (b) as a mixture of a reducible chromium salt and a reducing agent for the same, or (c) as chromium present in the metallic matrix of the composite, or (d) as a combination of (a), (b) and (c) or any two of them.

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(1 METAL MATRIX The metals which constitute the major portion of the composite comprise those metals which when formed into compacted solid shapes from originally finely divided, powdered or otherwise particular shapes, e.g. by powder metallurgy techniques, are then sufficiently malleable to be worked and shaped by wire drawing, swaging, rolling and similar techniques. The metals or alloys should melt at temperatures below 3000 F. and should be metals which alloy readily with chromium, Suitable metals which may be used alone or in admixture with one another, or as the basis of alloys useful in the composites of this invention include copper, iron, nickel and cobalt and alloys based on one or more of these metals such as brass, bronze, and particularly alloys including chromium and/or aluminum and/or manganese. The examples which follow it is to be understood that only a relatively small number of the numerous alloys which are suitable in the composites of this invention are exemplified by way of. illustration, and that the invention applies with equal validity to many other metals and alloys having the properties specified above. In the practice of this invention it is preferred that the metal be in the form of minus 325 mesh powder, but it may also be utilized as relatively short wires, turnings or other small pieces provided suitable steps are taken to insure that a uniform mixture of metal and inorganic fiber is obtained.

(2) INORGANIC FIBER The inorganic fiber which serves as the reinforcement for the metal matrix material is the alpha alumina or sapphire fiber produced as described in United States Patent 3,077,380, issued February 12, 1963 or the complexed alumina fiber described in United States Patent 3,023,115, issued February 27, 1962. As therein described, the sapphire or modified sapphire fibers are produced by melting aluminum and then bringing hydrogen gas dried to a moisture content of preferably about 3 to 5 parts by weight of water vapor per million parts of hydrogen, by Weight, while the melt is maintained at a temperature between about 1370 C. and 1510" C., and condensing a fibrous aluminum oxide on a refractory oxide containing condensing surface exposed to the vapor phase above the melt. By utilizing the techniques taught in the above application and patent, alumina filaments with diameters between about 0.5 micron and 7 microns and with lengths of from about of an inch up to /2 inch, and having tensile strengths between 2 10 and 3x 10 p.s.i. are readily produced. To prepare the preferred woollike filaments or fibers for the present invention the fibers are slurried in distilled water in the proportions of about 5 parts of fiber by weight to parts of water by weight or volume. This water slurry is then agitated violently for about 1 minute in an intensive stirrer such as a Waring Blendor, after which the slurry is dewatered, e.g. by filtration. The fibers are then dried on the filter paper and removed for further use. By proceeding in the manner indicated, the original wool product is transformed from an initially clumped, tangled mass of randomly oriented bunched filaments, to a dispersed product of loose individually separable fibers from which the fibers are readily oriented when mixed and processed as described below.

3 (3) THE BOND PROMOTING COMPONENTS The third essential component of the composites constituting the present invention comprises a complex of substances the function of which is not fully understood, but which appear to bring about a mutual wetting of the metal matrix and the sapphire fibers. It has been observed that without these substances, no matter how the sapphire fibers are oriented, a dispersion of fibers in the metal matrices described below and processed to produce maximum density (100%) yields a material with properties which represent a dilution of the properties of the metal matrix. Indeed in some instances sufiicient heating to produce increase in density in compacts formed of metal or alloy and fiber completely degrades the fiber and destroys its integrity. In view of this, a most important aspect of the novel composites of this invention resides in the selection of suitable bond-producing or bond-inducing materials.

It has been found that the presence of two classes of metal ions is essential for the realization of the desired bond between the metal matrix and the alpha alumina reinforcing fibers or filaments.

The first of these is selected from the group consisting of calcium, strontium, barium and magnesium, that is the alkaline earth metals and magnesium, and these are added to the mixture of the two other components in the form of an aqueous solution of one or more water-soluble salts of the indicated metals, for example as a halide, acetate or nitrate of the alkaline earth metal.

The other metal, the presence of which appears to be essential, is chromium. The chromium may be present in the alloy, or it may be available on the surface of the metal granules as a chromium compound, or partly as one and partly as the other. It has also been found that the chromium may be provided by initially dispersing a chromium salt throughout a mixture of metal and fiber and then reducing the chromium compound to the metal during a subsequent firing step.

From experiments conducted with mixtures from which either the alkaline earth metal compound or the chromium supplying material or both were omitted from mixtures of metal and alumina fiber, it was found that the absence of either of the bond-promoting constituents was fatal to the formation of the desired bond. As a consequence it would appear that the cement or bond is probably a reaction product of an alkaline earth metal ion, chromium preferably in the form of an active compound supplying the chromium as an ion and aluminum oxide. Under the later described firing conditions, the combination might exist as an alkaline earth chromite such as calcium chromite which then either reacts with or is soluble to a limited extent in the surface layer of aluminum oxide on the filaments. Possibly the presence of chromium as an oxide, at some stage of the process, is necessary to control the depth of penetration of the bond into the fiber to avoid total degradation of the fiber.

(4) PROPORTION S In addition to the foregoing, it has been found that the ratios of the various constituents considered to be utilized for the development of wetting properties must be within rather narrow limits relative to each other in order for the desired effect to take place. For example, the amount of calcium ion should be of the order of 0.07 to 0.2 part by weight in 2 parts by weight of fiber and the amount of chromium, probably in the form of oxide dispersed on the surface of the metal matrix should be equivalent to a range equivalent to by weight up to 100% by weight of the alkaline earth ion in question.

A specific example of such optimum ratio in the case of calcium ion would represent a composition somewhat as follows: 100 parts by weight of minus 325 mesh nickel powder, 0.05% chromium ion presented to the composition e.g. as chromic chloride, and 0.15 part by weight of calcium ion presented e.g. as calcium chloride of formula CaCl -2H O, and 2 parts by weight of sapphire fiber.

Dealing with volume percentages only and calculating back from the weight percents in this example to provide an inference as to the thickness of interface between the metal matrix and the aluminum oxide fibers, the indications are that an amount of calcium ion needs to be utilized which represents a coverage on the surface of the aluminum oxide fiber varying between 30 A. and A. in thickness. If the amount of calcium ion excecds these limits to any large extent the degree of reinforcement drops and if the amount of chromium ion present at the interface exceeds the amount of calcium, again the reinforcement drops. The inference, therefore, is that the thickness of the interface in fully fired form (to produce 100% density) is in the range of 20 A. to 60 A. units in thickness and this represents a gradual modification of composition from the metal phase to the reinforcement phase without destruction of the integrity of the fiber. In addition, this interface must have mechanical properties in shear and tension at least as good as the aluminum oxide fiber itself.

It has been stated previously that one of the elements which may be utilized as assist for the preparation of the interface is an element taken from the class magnesium, calcium, strontium and barium. Of these calcium is preferred for reasons of economics and ease of handling. In determining the optimum amount of this constituent for production of maximum reinforcement under a specific series of consolidation procedures for the base metal, the effect of variation of the amount of ion in this series was determined. It was found that 1 part by weight of calcium ion was approximately equal to its effectiveness to about 1 part by weight of magnesium ion and that rough 1 /2 parts by weight of strontium ion was required to match the effect of 1 part by weight of calcium ion and approximately 2 parts by weight of barium ion were needed to match the effect of 1 part by weight of calcium ion with respect to the achievement of equivalent reinforccment of a nickel chromium alloy utilizing sapphire fibers. Within limits of experimental error in this complex field, these ratios are approximately equivalent to the ratios of the specific gravities of the respective oxides of these elements and as a consequence represents further confirmation as to an optimum thickness of interface between the metal matrix and the fiber system as being roughly in the range of 30 A. to 100 A. in extent.

A final relationship exists with respect to variation of the relative ratio of weight of fiber per weight of matrix and again experimental evaluation indicates the significant factor is the surface area of fiber exposed. Again, referring back to a specific system which produces the desired amount of chromium compound at the interface automatically as a function of processing it is found that the amount of calcium ion, for example, required to produce the optimum of reinforcement for a specific amount of fiber will be in the ratio of 0.7 to 2.0 parts by weight of calcium ion to 20 parts by weight of the type of fiber described previously. Referring again to a specific example where chromium ion must be deliberately added as in the case of 100 grains of 325 mesh pure nickel powder, the amount of chromium ion by weight found to be most effective varies between 0.01 to 0.1% by weight. The amount of calcium ion found to be most effective varies between 0.07 and 0.13% by weight all referred to 2% by weight of aluminum oxide fiber, and the percentage figures calculated on 100 grams of metal base.

The fiber content determines the amount of calcium ion disposed in an optimum thickness on the surface of the fiber. Again, by experimentation it is determined that if the amount of fiber by weight is increased from 2% to 16% in a nickel chromium base, the optimum amount of calcium ion for producing maximum wetting (this being determined by establishing the maximum strength achieved through utilization of the calcium ion as a web ting agent) then increased to about 1.5%.

A still further control appears to be necessary as far as the chromium content is concerned. For alloys containing significant amounts of chromium in their constitution in powder form no added chromium is required for wetting purposes providing at least 5% chromium is present in the alloy and providing the amount of fiber does not exceed 5% by weight of the types given in the foregoing descriptions. Outside of these limits chromium needs to be added deliberately. It appears that by virtue of the methods utilized for the consolidation of these metal systems that alloys containing between 5 and 20% chromium will produce a modified chromium oxide on the surface of the individual granules which will accommodate the ratios previously given between chromium ion, calcium ion and fiber. If the chromium oxide content is less than the 5% minimum limit given then chromium ion needs to be added to the composition. If the amount of chromium in the base metal is less than 20% and the amount of fiber utilized is greater than 5%, then again chromium ion needs to be added to the compositions.

The specific inference obtained from such evaluations confirms the numerical ratios given before and for purposes of emphasis these numerical ratios will be repeated. For a specific weight of sapphire fiber utilized for reinforcement, the optimum weight percent range of alkaline earth ion referring specifically to calcium is 0.035 to 0.1 port by weight for each part by weight of sapphire fiber and the optimum weight of chromium ion relative to the fiber is in a range between 0.5 and 5% of the weight of fiber.

(5) METHOD OF PREPARATION OF THE COMPOSITES As shown schematically in the flow sheets accompanying this description, two methods have been developed for the preparation of composites in 100% density form and in which the reinforcement is disposed in a preferred orientation in which the fibers or filaments are oriented along the longitudinal axis of the final product. In addition, both methods provide products which may be worked so as to produce rod, wire, sheet and the like in which the fibers are oriented longitudinally along the axis of greatest anticipated stress.

The first method schematically shown in FIGURE 1 is based on powder metallurgy techniques similar to those described in my United States Patent 2,593,943, issued on April 22, 1952, insofar as it includes extrusion of a plastic mass at room temperature using a fugitive binder which is eliminated in a subsequent sintering Step. In the second method, outlined in FIGURE 2, a suitable mixture of metal matrix and fiber reinforcement materials containing materials which promote the bonding of the two to one another, is heated to the fusion temperature of the metallic constituents, in a specialized container. Both methods will next be described in detail.

5(a) EXTRUSION-SINTERING METHOD OF FIGURE 1 In the first procedure, a plastic mass is produced by mixing the metallic or alloy portion of the composite with the desired proportion of sapphire fibers. The metallic material has preferably been comminuted to minus 325 mesh (Tyler Standard) powder in order to facilitate mixing to a uniform product. Mixing is accomplished at room temperature and a plasticizcr or extrusion agent such as methyl cellulose, guar gum, gum tragacanth or other mentioned in my Patent 2,593,943 is included in the metalfiber mixture prior to mixing. The charge to the mixing apparatus is completed by addition of a water solution of the required amount of alkaline earth salt, with or without the addition of a water-soluble chromium compound.

The charge is kneaded until a plastic mass is achieved and is then transferred to an extrusion apparatus. Ex-

trusion is accomplished at room temperature, the die size being chosen so that the area reduction from the bore of the charging cylinder to the opening in the die is at least a ratio of 16:1. Such an area reduction causes almost all of the fibers to line up in the direction of the extrusion without any substantial breakage of the fibers. After extrusion the resulting rod is dried for about 1 hour at 325 C., the temperature and duration of this step being variable to some extent dependent on the size of the extrusion and the specific materials being handled. The dried rod is then heated to sintering temperature in a stream of hydrogen which has been dried to a dew point between minus 10 C. and minus 50 C., flowing at a rate of approximately 1 liter per minute.

After reaching sintering temperature, the dried extrusion is held at the sintering temperature for about 1 hour and as a result achieves an apparent density of between 80% and 90% of theoretical density. The sintered rod is then cooled in a hydrogen atmosphere. When cool, the rod is put through a wire rolling mill to reduce its diameter by at least 10% and not more than Thereafter the cold reduced rod is reheated in hydrogen to the sintering temperature and maintained at that temperature for 1 hour, in a stream of hydrogen dried to the extent indicated above.

As a consequence of the processing described, the composite achieves a density of between 98% and 100% of theoretical. Usually a composite possessing 100% of theoretical density is obtained. The products may be rolled, drawn, swagcd or otherwise worked to any finished size.

To further illustrate the above method, the following specific example illustrates the preparation of a sapphire fiber reinforced 30 Ni-- Cr composite, with and without the addition of the bond promoting component essential to this invention.

One hundred grams of minus 325 mesh 80 nickel-20 chromium power is thoroughly mixed with 1 gram of methyl cellulose characterized by a standard viscosity of 15,000 cps. 8 ccs. of water are added and the mass is then kneaded until the water is fully dispersed and the methyl cellulose has achieved a fully swollen condition. The material is then extruded at a pressure of 4,000 lbs. per square inch in a die the cross section of whose bore has a cross section area 16 times that of the die orifice. The extrusion produces a rod /4" in diameter. The rod is then placed in an oven at room temperature and the temperature is raised to 325 C. over a space of minutes, after which the rod is removed from the furnace. The rod is then placed on coarse fused zirconia (minus mesh) and brought to a temperature of 2320 F. in a space of 1 hour utilizing hydrogen at a flow rate of 1 liter per minute and exhibiting a dew point throughout the run varying from 20 C. to 40 C. The temperature and hydrogen rate just indicated is maintained for 1 hour after which the furnace is turned off and the specimen is allowed to cool to room temperature in the flowing hydrogen atmosphere. The specimen is then removed from the furnace after which the diameter is found to be 0.22. The sintered specimen is then put through a wire rolling mill as a result of which its diameter is reduced to 0.20. The rolled specimen is then replaced in the hydrogen furnace and under the flowing conditions of hydrogen previously described, the temperature is again brought to 2320 F. and maintained at this level for 1 hour after which the specimen is again cooled with the furnace in hydrogen. The density of the specimen under these conditions is found to be 8.13.

Using successive passes on the wire mill the diameter of the specimen is then reduced to 0.05". The tensile strength of such a specimen is then measured on a Baldwin Southwark tensile testing machine and the average of 5 such specimens produced in the manner just described yields a value of 160,000 lbs. per square inch.

The Metals Handbook records an exactly identical value for cold-worked Nichrome.

To illustrate the reinforcing capabilities of the sapphire fibers previously described, the procedure as just detailed is repeated except that the raw batch comprises the following materials: 100 grams of -325 mesh 80 nickel-20 chromium powder; 1 gram of 15,000 cps. methyl cellulose; 2 grams of sapphire fibers; to this dry mixture is added 8 ccs. of a water solution containing 0.55 gram of di-hydrated calcium chloride (approximately equivalent to 0.15 gram of calcium). This plastic mixture is kneaded, extruded, presintered, rolled, final sintered and roll reduced as before and on measuring the average of the tensile strength of five specimens made in this manner an average value of 260,000 lbs. per square inch tensile strength is obtained.

(b) FUSION METHOD-FIGURE 2 In order to simplify the preparation of composites and to greatly diminish the time required for their preparation, the procedure shown in FIGURE 2 may be utilized.

Either of two variants may be used, depending on whether or not there is a sufficient amount of chromium in the metallic portion of the charge. Since the presence of at least chromium in the metal matrix permits a simpler processing this modification will be described next.

All of the ingredients-metal or alloy powder, sapphire fibers, and alkaline earth salt solution-are mixed as in the preceding description, the methyl cellulose being omited. The mixture is then dried in an oven at about 325 C. after which it is broken down lightly in a mortar using a rubber pestle. A quartz tube is then provided with one closed end and an open end and the dried mixture in comminuted form is then poured into the tube. The quartz tube is then dropped bottom end down into a piece of insulating refractory having a hole of appropriate size drilled therein and exhibiting a wall thickness around the hole not greater than A". An advantage is obtained by restricting somewhat the size of the open hole in the quartz tube but making sure that the size is never less than /s" across. The assembly is then placed immediately in a furnace heated to a temperature depending on the type of metal used and designated in Table 1 as the fusion temperature. It has been found from experience by insertion of suitable thermocouples that the quartz tube will achieve the temperature of the furnace in approximately 5 minutes under these conditions. maintained at this temperature for 3 minutes longer after which it is immediately removed from the furnace. A product exhibiting 100% density is thereby achieved.

On rolling the specimen thus prepared down to the 0.05" wire diameter, tensile strengths are achieved which are substantially identical with those obtained in the procedure previously described involving double sintering in hydrogen.

As a specific example of this method of processing 100 grams of 325 mesh powder of the 80 nickelchrome alloy are mixed with 2 grams of sapphire fibers. The dry mix is wet down with 10 ccs. of a water solution containing 0.56 gram of dihydrated calcium chloride (CaCl -2H O). After thorough mixing the mass is dried for 1 hour at 325 C. after which it is again rubbed to a powder gently in a porcelain mortar using a rubber ended pestle. The powder is then filled in a quartz tube with a closed end, said quartz tube having a length of 8" and a diameter of 7 A piece of K- insulating brick is provided of square cross section 1" on an edge and 7" high, A hole is drilled in the longitudinal center of this brick sufficiently large to accommodate the quartz tube rather tightly. The open end of the quartz tube is shrunk with an oxyhydrogen torch until the hole remaining has a diameter of approximately /a. The

The specimen and its assembly is then assembly is then placed in a furnace which has been previously brought to 2600 F. and 8 minutes after the furnace door is closed, the furnace door is opened and the hot assembly is removed to room temperature and allowed to cool. After cooling, the brick and quartz envelop is broken away from the fused specimen and the specimen is then rolled down in a wire mill through the use of successive passes to a diameter of 0.05". The average value of 5 specimens produced in this manner was a tensile strength of 260,000 lbs. per square inch.

The atmosphere provided by such a combination inside the quartz tube is, in the main, essentially neutral or at best slightly oxidizing. The air in the tube is completely replaced with the water of hydration available through decomposition of the calcium chloride hydrate which is used as an additive and in most cases where the chromium content of the alloy of the type listed in the table is in excess of 10%, this is sufficient to produce good sintering without oxide inclusions of the grain boundary other than the aluminum oxide fibers indicated. By virtue of the excessive speed of melting and the sluggishness with which such melting takes place in the very short cycling utilized for this purpose, the fibers tend to stay pretty much in the place originally positioned when made available in the original raw batch form. Cross sections have established that some degree of longitudinal orientation is available in the melting cycle and this is brought to a completely longitudinal orientation in the subsequent rolling.

However, alloys containing less than 10% chromium, e.g. alloys 4, 5 and 6 in Table I, show a slight but significant degree of oxidation in the water atmosphere thus produced. As a consequence of such oxidation, attack on the fiber tends to be excessive and an important portion of the integrity is lost even though powerful bonding to the structure is obtained.

To eliminate this slightly oxidizing condition, a dry pressed pellet of either titanium hydride or zirconium hydride is inserted in the bottom of the tube and is separated from the mass of the material being fused by a layer of granular fused zirconia at least 18th of an inch thick. Usually an amount of titanium hydride or zirconium hydride equivalent to about 10% by weight of the specimen being fused is sufficient to ensure a substantially pure hydrogen atmosphere during the period of incipient and final fusion and under such conditions all oxide films which would normally develop as a result of oxidation by water vapor are eliminated.

As further evidence that a combination of fiber and calcium ion is necessary simultaneously, it was found that a combination of nickel20 chromium alloy powder with 2% fiber without calcium, no matter how processed, yielded an average tensile strength after rolling of 150,000 to 156,000 pounds and a combination of 80 nickel-20 chromium alloy powder with CaCl -2H O but without fiber, and no matter how processed, yielded an average tensile strength of 152,000 to 155,000 pounds per square inch.

Hence with the 8020 NiCr alloy the following tensile strengths were obtained:

P.s.i. NiCr (no additive) 165,000 NiCr plus fiber 156,000 NiCr plus alkaline earth salt 152455.000 NiCr plus both fiber and alkaline earth salt- 260,000

Components of the compositions indicated below were prepared in accordance with the methods described above and after such preparation were tested for tensile strengths. The results were compared with the results obtained for otherwise similar metal/alloy-fiber composites prepared without the use of alkaline earth metal and/or chromium additives. The results are shown in Table 1 below.

TABLE 1 TENSILE STRENGTH F COLD WORKED 0.05 DIAMETER WIRE WITHOUT AND WITH REINFORCEMENT Sinter Fusion Percent Percent Fiber Tensile Tensile Composition Metal or Alloy, Temp, Temp, Added Added Parts, by Strength, Strength, No. 100 pts./wt. F. F Weight p.s.1., No p.s.i., Al1 Ca Ion Cr Ion Additives Additives 1, 800 2, 000 0. 2 0. 1 2. 0 66, 000 100, 000 2, 550 2, B50 0. 2 0. 05 2. 0 82, 000 180, 000 i 2, 450 2, 750 0. 2 0. 05 2. 0 145, 000 245, 000 45 Ni-55 Gu 2, 100 2, 350 0. 2 0. 1 2. 0 135, 000 230, 000 67 Ni33 Cu 2, 300 2, 000 0. 2 0. l 2. 0 135, 000 235, 000 07 (Du-5 Ni-2l Mn 1, 900 2, 400 0.2 0.10 2. 0 110, 000 200, 000 60 Ni-24 Fe-16 Cr"... 2, 450 2, (S50 0. 0 2. 0 135, 000 235,000 72 F8 23 (Tr-5 A] 2, 650 2,800 0. 1 0 2. 0 175, 000 270,000 2, 320 2, G00 0. 15 0 2. 0 165, 000 200, 000 2, 320 2, 600 0. 4 0 4. 0 105, 000 340, 000 2, 340 650 0. 8 0. 05 8. 0 105, 000 400, 000 2, 340 2, 050 1.6 0. 10 10. 0 165, 000 780, 000

Having now described this invention in accordance with the patent statutes it is not intended that it be limited except as may be required by the appended claims.

I claim:

1. The method of preparing a composite consisting of a metal matrix containing between 1.5% and by weight, based on the weight of the metal matrix, of sapphire alpha alumina fibers having lengths between about 0.0625 and 0.5 inch and diameters between about 0.5 and 7 microns, and, as material promoting a bond between said fibers and said metal matrix at least one alkaline earth compound; there being present an amount of alkaline earth metal correponding to from 3.5 to 6.5 parts by weight of calcium, on a weight basis, per 100 parts of said alumina fiber on a weight basis and there being present at the surfaces of said metal exposed to said alumina an amount of chromium corresponding to between 0.1 and 1% by weight of the fibers which comprises: forming a mixture containing (1) comminuted metal selected from the group consisting of copper, iron, nickel and cobalt and alloys of said metals with at least one other metal selected from the group consisting of chromium, aluminum, manganese, copper, iron, and nickel, (2) said fibers of alpha alumina, and a water solution of a salt of an alkaline earth metal; drying the mixture by heating same; shaping the dried product; consolidating the dried product by heating to a temperature at least sufiicient to sinter same and thereafter cold working the consolidated product to finished size and shape.

2. The method of claim 1 wherein the original mixture contains an amount of alkaline earth metal equivalent to 0.2 to 1.6% by weight of calcium, up to 0.10% by weight of added chromium as a water soluble chromium salt and between 2 and 16% by weight of alumina fibers.

3. The method of claim 1 wherein the metallic matrix material in the first formed mixture is powder.

4. The method of claim 1 wherein the metallic matrix material in the first formed mixture is bundled wire.

5. The method of forming a composite consisting of a metal matrix consisting of metal selected from the group consisting of metals and alloys which alloys readily with chromium and which melt at temperatures below 3000" F., said metal matrix containing between 1.5% and 20% by weight, based on the weight of the metal matrix, of sapphire alpha alumina fibers having lengths between about 0.0625 and 0.5 inch and diameters between about 0.5 and 7 microns, and, as material promoting a bond between said fibers and said metal matrix at least one alkaline earth compound; there being present an amount of alkaline earth metal corresponding to from 3.5 to 6.5 parts by weight of calcium, on a weight basis, per 100 parts of said alumina fiber on a weight basis and there being present at the surfaces of said metal exposed to said alumina an amount of chromium corresponding to between 0.1 and 1% by weight of the fibers which comprises: forming an extrudable mixture containing metal powder, sapphire fibers, a plasticizer, and a water solution of an alkaline earth salt; extruding the mixture at room temperature with an area reduction of at least 16 to 1; drying the extrusion at about 325 C. for one hour; heating the dried extrusion to the sintering temperature of the mixture in a stream of hydrogen; holding the sintered material at the sintering temperature for about 1 hour; reducing cross section area of the product between 1015% by cold working; reheating the cold worked product to the original sintering temperature in flowing hydrogen; retaining same at temperature for about 1 hour and cold working the reheated product to finished size and shape.

6. The method of claim 5 wherein about 0.1% chromiium is added to the initial mixture as a water soluble chromium salt.

7. The method of claim 5 wherein a metal hydride is inserted in the refractory sleeve whereby the reducing atmosphere is provided during said rapid heating to the fusion temperature.

8. The method of preparing a composite consisting of a metal matrix consisting of metal selected from the group consisting of metals and alloys which alloy readily with chromimum and which melt at temperatures below 3000 F., said metal matrix containing between 1.5% and 20% by weight, based on the weight of the metal matrix, of sapphire alpha alumina fibers having lengths between about 0.0625 and 0.5 inch and diameters between about 0.5 and 7 microns, and, as material promoting a bond between said fibers and said metal matrix at least one alkaline earth compound; there being present an amount of alkaline earth metal corresponding to from 3.5 to 6.5 parts by weight of calcium, on a weight basis, per 100 parts of said alumina fiber on a weight basis and there being present at the surfaces of said metal exposed to said alumina an amount of chromium corresponding to between 0.1 and 1% by weight of the fibers which comprises: forming a mixture containing metal powder, sapphire fibers, and a water solution of an alkaline earth metal salt; drying the mixture at about 325 C. to form a dried cake; breaking down the dried cake into a mortar; pouring the distintegrated cake into a quartz tube; inserting tube in an insulating refractory sleeve; heating same rapidly to fusion temperature of the mixture; maintaining the sleeve and its contents at the fusion temperature of the mixture for about 3 minutes; removing the mixture from the sleeve after it has been cooled to a solid; and working said solid to final size and shape.

References Cited by the Examiner UNITED STATES PATENTS 2,741,828 4/1956 Matthew et a1 29-191.2 2,746,134 5/1956 Drummond 29-1912 2,932,883 4/1960 Weber 29420.5 3,011,870 12/1961 Webb et a1. 23-142 3,047,383 7/1962 Slayter 29--182.5 X 3,060,098 10/1962 Gershon 51-309 3,085,876 4/1963 Alexander et al. -206 3,150,444 9/1964 Reen 29420.5

JOHN F. CAMPBELL, Primary Examiner.

HYLAND BIZOT, MORRIS LEIBMAN, Examiners.

Claims (2)

1. THE METHOD OF PREPARING A COMPOSITE CONSISTING OF A METAL MATRIX CONTAINING BETWEEN 1.5% AND 20% BY WEIGHT, BASED ON THE WEIGHT OF THE METAL MATRIX, OF SAPPHIRE ALPHA ALUMINA FIBERS HAVING LENGTHS BETWEEN ABOUT 0.0625 AND 0.5 INCH AND DIAMETERS BETWEEN ABOUT 0.5 AND 7 MICRONS, AND, AS MATERIAL PROMOTING A BOND BETWEEN SAID FIBERS AND SAID METAL MATRIX AT LEAST ONE ALKALINE EARTH COMPOUND; THERE BEING PRESENT AN AMOUNT OF ALKALINE EARTH METAL CORRESPONDING TO FROM 3.5 TO 6.5 PARTS BY WEIGHT OF CALCIUM, ON A WEIGHT BASIS, PER 100 PARTS OF SAID ALUMINA FIBER ON A WEIGHT BASIS AND THERE BEING PRESENT AT THE SURFACES OF SAID METAL EXPOSED TO SAID ALUMINA AN AMOUNT OF CHROMIUM CORRESPONDING TO BETWEEN 0.1 AND 1% BY WEIGHT OF THE FIBERS WHICH COMPRISES: FORMING A MIXTURE CONTAINING (1) COMMINUTED METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, IRON, NICKEL AND COBALT AND ALLOYS OF SAID METALS WITH AT LEAST ONE OTHER METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, ALUMINUM, MANGANESE, COPPER, IRON, AND NICKEL, (2) SAID FIBERS OF ALPHA ALUMINA, AND A WATER SOLUTION OF A SALT OF AN ALKALINE EARTH METAL; DRYING THE MIXTURE BY HEATING SAME; SHAPING THE DRIED PRODUCT; CONSOLIDATING THE DRIED PRODUCT BY HEATING TO A TEMPERATURE AT LEAST SUFFICIENT TO SINTER SAME AND THEREAFTER COLD WORKING THE CONSOLIDATED PRODUCT TO FINISH SIZE AND SHAPE.

8. THE METHOD OF PREPARING A COMPOSITE CONSISTING OF A METAL MATRIX CONSISTING OF METAL SELECTED FROM THE GROUP CONSISTING OF METALS AND ALLOYS WHICH ALLOY READILY WITH CHROMIMUM AND WHICH MELT AT TEMPERATURES BELOW 3000* F., SAID METAL MATRIX CONTAINING BETWEEN 1.5% AND 20% BY WEIGHT, BASED ON THE WEIGHT OF THE METAL MATRIX, OF SAPPHIRE ALPHA ALUMINA FIBERS HAVING LENGTHS BETWEEN ABOUT 0.0625 AND 0.5 INCH AND DIAMETERS BETWEEN ABOUT 0.5 AND 7 MICRONS, AND, AS MATERIAL PROMOTING A BOND BETWEEN SAID FIBERS AND SAID METAL MATRIX AT LEAST ONE ALKALINE EARTH COMPOUND; THERE BEING PRESENT AN AMOUNT OF ALKALINE EARTH METAL CORRESPONDING TO FROM 3.5 TO 6.5 PARTS BY WEIGHT OF CALCIUM, ON A WEIGHT BASIS, PER 100 PARTS OF SAID ALUMINA FIBER ON A WEIGHT BASIS AND THERE BEING PRESENT AT THE SURFACES OF SAID METAL EXPOSED TO SAID ALUMINA AN AMOUNT OF CHROMIUM CORRESPONDING TO BETWEEN 0.1 AND 1% BY WEIGHT OF THE FIBERS WHICH COMPRISES: FORMING A MIXTURE CONTAINING METAL POWDER, SAPPHIRE FIBERS, AND A WATER SOLUTION OF AN ALKALINE EARTH METAL SALT: DRYING THE MIXTURE AT ABUT 325*C. TO FORM A DRIED CAKE; BREAKING DOWN THE DRIED CAKE INTO A MORTAR; POURING THE DISTINTEGRATED CAKE INTO A QUARTZ TUBE; INSERTING TUBE IN AN INSULATING REFRACTORY SLEEVE; HEATING SAME RAPIDLY TO FUSION TEMPERATURE OF THE MIXTURE; MAINTAINING THE SLEEVE AND ITS CONTENTS AT THE FUSION TEMPERATURES OF THE MIXTURE FOR ABOUT 3 MINUTES; REMOVING THE MIXTURE FROM THE SLEEVE AFTER IT HAS BEEN COOLED TO A SOLID; AND WORKING SAID SOLID TO FINAL SIZE AND SHAPE.

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