US2922721A - Method for coating and infiltrating a porous refractory body - Google Patents

Description

Jan. 26, 1960 s. E. TARKAN ET AL 2,922,721

METHOD FOR COATING AND INFILTRATING A POROUS REFRACTORY BODY Filed April 2, 1956 2 Sheets-Sheet 1 FIG. IE.

FIG. IB.

and $2110.? 6. 6057251.

FIG. IA.

Jan. 26, 1960 s. E. TARKAN ET AL 2,922,721

METHOD FOR COATING AND INFILTRATING A POROUS REFRACTORY BODY Filed April 2, 1956 2 Sheets-Sheet 2 .5 IQF'ACE R p 6 a 7 x i 5 5 i 7x A 1! Y {a j COAT/N6 I N V EN TORS 572/44? TE. 72.?K/IV, #5440!!! Z Ih EWQ METHOD FOR COATING AND INFIL'IRATING A POROUS REFRACTORY BODY Stuart E. Tarkan and Henry W. Lawendel, New York,

and Claus G. Goetzel, Yonkers, N.Y., assignors to Sintercast Corporation of America, Yonkers, N.Y., a corporation of New York Application April 2, 1956, Serial No. 576,230 11 Claims. (21. 117-55 The present invention.- relates to coated refractory metal compound composites, and more particularly to a method for obtaining adherent metal coatings upon refractory metal carbide materials characterized by improved metallurgical'quality, improved resistance to oxidation, improved resistance to thermal and mechanical impact or shock, and generally improved properties at elevated temperatures.

The advent of modern jet engines, rockets and other types of prime movers involving heat engines operating at elevated temperatures ofup to about 1000 C. and higher has provoked intensive research in the development of high temperature materials, particularly in the development of thermal elements, for example fluid guiding elements such as turbine blades, buckets, nozzles, vanes, guides, partitions, etc., which inuse are exposed to corrosive gaseous atmospheres. The use of special fuels containing lead compounds, vanadium compounds and other compounds either present as additives or inherent in the fuel composition have been particularly troublesome in view of harmful vapors of lead oxide, vanadium pentoxide, etc. which are given off during combustion of the fuel and which readily chemically attack and corrode unprotected component parts of heat engines at elevated temperatures.

In an attempt to solve the foregoing problem, certain wrought and cast heat resistant alloys of special corrosion resistant compositions were. developed. However, these alloys were limited in their application because of their melting points which range in the neighborhood of about 1300 C. to 1500 C. As more powerful jet engines were designed to operate at higher temperatures, additional burdens were placed on these alloys which had to be replaced by more stable materials of higher melting point.

An outstanding material which was developed and proposed to meet this need was a refractory carbide material consisting of about equal proportions by weight of titaniurn carbide and an alloy of the so-called super alloy type usually containing nickel or cobalt as major alloying constituents, and chromium, tungsten, molybdenum, titanium, iron, aluminum, etc. as other alloying constituents. This material could either be prepared by the well-known cementing method employed in the powder metallurgical production of carbide tools, that is by mixing refractory carbide particles with a given amount of binder metal, for example nickel or cobalt or an alloy based on these metals, followed by pressing the mixture into a desired shape and thereafter sintering it; or the material could be produced by forming a sintered porous skeleton comprising a refractorymetal carbide and thereafter infiltrating it with a heat resistant metal or alloy to form a strong composite structure. The latter method was preferred over the former as it enabled the consistent production of superior materials. It was found that thermal elements produced by infiltration comprising about 50% by Weight of titanium carbide and about 50% by weight of a nickel base alloy containing about 13% 2,922,721 Patented Jan. 26, 1960 to 15% chromium and about 6% to 7% iron as alloying constituents could withstand a stress of about 42,000 p.s.i. at a temperature of about 875 C. for 100 hours in an oxidizing atmosphere before it would rupture. Itwas, also found that the same material at 985 C. would withstand a stress of 16,000 psi. before it would rupture after 100 hours of testing. At the lower temperature, the thermal elements after testing exhibited an elongation of the order of about 2% to 3% and an impact strength of about 10 ft. lbs. for a Charpy-type unnotched bar, while at the higher temperature they exhibited an elongation of about 4% to 8% and an impact strength of about 6.5 ft. lbs.

The foregoing properties have been found satisfactory for parts to be used in short time applications in jet engines, and performance records of up to about 100 hours have been established in actual service tests. However, present demands for increasedservice life under more aggravated service conditions prevailing in the latest jet engine and rocket designs have necessitated the development of even better high temperature materials. It was found that it was necessary to improve oxidation resistance, strength, thermal shock and impact resistance of refractory metal carbide composition at temperatures in the range between 950 C. and 1050 C. and bring these properties in closer accord with the extremely good properties which were established for these same materials at 875 C. v

It was observed that while these materials were a substantial improvement over Wrought or cast heat resistant alloys, they tended to fail during prolonged service as a result of surface deterioration due to oxidation and cor-' rosion at temperatures above 900 C. and of the order of about 950 C. to 1050 C. It was found that surface, deterioration would occur due to corrosion which markedly deleteriously affected the impact resistance and strength of the material. The failure was usually of a type characteristic of brittle materials. It was felt that, in order to inhibit such surface attacks and sustain the properties of the material, it would be necessary to'provide a protective surface coating around the exposed working surfaces of the metal carbide composite was to protect it from hot corrosive atmospheres. Various, methods have been proposed for providing such protective coatings to refractory'compound composites. Thus, according to US. Patent No. 2,714,245, granted to Claus G. Goetzel on August 2, 1955, and assigned to the present assignee, the protective coating could be achieved during infiltration, of a porous skeleton body by first producingthe porous body (.e.g. a turbine blade) slightly undersized, centering it in the cavity of a mold comprising a substantially inert refractory, the cavity conforming in shape to but being slightly larger than the body, infiltrating the body and allowing for suificient excess infiltrant to fill the space between the blade and the mold walls to provide for the coating. Coatings of controlled thickness produced in this manner markedly improve the properties of turbine buckets, providing extreme care was taken in indexing the skeleton in the mold cavity to insure obtaining the desired coating dimensions and also provided the heating cycle was carefully controlled to minimize non-uniformshrinkage or warpage of the inert refractory. Also care had to be taken to control the infiltration process so that the infiltrant'metal during infiltration did not gush down the sides of the skeleton and erode its surface.

In copending application U.S. Serial No. 485,568, filed January 28, 1955, in the names of Claus G. Goetzel,

Nicholas J. Grant, Leonard P. Skolnick and Jack A.-

Yoblen, and assigned to the present assignee, a method for coating refractory metal compound composites is disbonded, relatively ductile coating by controlling the relative temperatures of the composite and the cbatingma:

teriall so as to'preverit embrittle'rnent of the coating by excessive diffusion of the base material into it. Improved results could be consistently obtained by this; concept provrdedzthe necessary care was 'taken to control the relative temperatures of the materials to be joined.

. The present invention differs over the'foregoing concepts m that an entirely new approach is utilized for coating metal compound composites produced by infiltratron. It is particularly applicable to the production of coated products having a tapered configuration, for example, fluid guiding members, such as turbine buckets or nozzle .vanes, characterized by a thick portion near the lead ng edge tapering smoothly and arcuately to a relatively thin trailing edge portion. Generally speaking, tapered bodies area little more ditficult to coat substantially uniformly, particularly when the coating is carried out simultaneously with infiltration in amold. Even whenihe skeleton fluid-memberis'properly indexed in a mold 'with'a space provided between .the'skeleton and the mold for receiving the infiltrant metal coating, movement of the body withinjhe'mold or movement of the mold walls themselves during heating isapt' to throw off the indexed skeleton sufliciently to effect deleteriou sly the uniformity of the coating. V

An improved method has now been discovered whereby ,the foregoing disadvantages are .greatly minimized wherein the skeleton body prior to infiltration is produced as a composite structure which obviates thenecessity of accurately indexing the skeleton in the mold when'producing a coated body by infiltration.

Another important advantage is that the improved method also minimizes erosion of the skeleton surface during the combined infiltration and. coating step. It is the object of the invention to provide a combined infiltration and coating process for producing coated infiltrated composites comprising a high melting point re fractory metal compound material, for example titanium carbide. I

Another object is to provide a method for producing a coating of improved metallurgical quality on infiltrated refractorymetal compound materials.

, These and other objects will more clearly' appear when taken in conjunction with the accompanying drawing wherein:

Figs. 1A to 1F depict inflow sheet arrangement the steps and materials which may be employed in carrying out an embodiment of the invention;

Fig. 2 illustrates an expanded view of the boundary conditions which prevail in an embodiment of the invention between the mold and the skeleton prior to in filtration in the production of a coated body;

Fig. 3 is. similar-to Fig. 2 but shows the penetration of the infiltrant metal into the interstices of the skeleton and the" primary coating by infiltration; and

Flg. 4 is a representation of a photomicrograph at 250' magnificationof a transverse section of the final productv showing a relatively sharp line of demarcation between the coating and the base material.

In carrying the invention into practice, the porous skeleton body to be infiltrated is provided with a foundation layer or primary coating of a metal alloyable with the infiltrant metal, the thickness of the primarymetal coating determining to a large extent thedesired thickness of the final coating. Once the skeleton body is prm vided with the primary coating, it need only be inserted in -a powder pack of substantially inert refractory, e.g. thoria, zirconia, beryllia, alumina, etc, without taking the usual precautions of indexing the body to insure a' coating of accurate dimensions. In other 'words, the

primary coating of the composite skeleton also serves mold comprises the porous skeleton on one side, a primary metal coating of desired thickness on the surface thereof and on the other side of the primary coating a back-up support of substantially inert refractory oxide material. The composite skeleton is subjected to infiltration in the usual manner with a matrixforming metal which flows through the skeleton filling u'p'the pores and on out through the surface thereof merging and al-' loying with the primary coating. The flowing of the molten infiltrant metal but of the skeleton surface and into the primary coating is referred to as exfiltration and the use of this and equivalent expressions hereinafter is meant to cover the aforementioned phenomenon.

The primary coating metal employed in carrying out the invention should be one which will combine with the infiltrant to form a coating having the desired properties, i.e. having resistance to corrosion, erosion and oxidation and adequate ductility, hardness, etc. The metal should have a melting point higher than the melting point of the matrix-forming infiltrant metal so that the foundation layer provided by the primarycoating will not be prematurely disrupted before completion of the exfiltration step. Thus it is preferred that the melting point of the coating metal should be atleast 50 degrees higher than the melting point of the infiltrant metal in the pores of the skeleton. Additionally,,the. primary metal coat should not combine with the material of the skeleton to form a liquid phase at a temperature below the melting point of the matrix-forming infiltrant metal.

Goodresults are obtained by applying the metal coating in particulate form, powdered metal being preferably employed as the primary coating metal, although the coating metal may be applied by wire spraying, metal plating, etc; V

In building up a primary coating on a skeleton surface from powdered metal, a suspension of the metal in a liquid containing a fugitive binder has been found very satisfactory. The concentration of metal powder in the liquid binder may range from 1' to 3 grams per cubic centimeter of binder solution. The coating may be applied by painting, spraying or dipping, which after drying forms a hard layer capable of withstanding the usual amounts of shock which prevail during handling, etc. The dried coating can be shaped to the desired thickness, making allowances for volume changes during treatment, and the coated skeleton inserted into an investment pack for heating to remove the fugitive binder and to sinter to some degree the metal powder to form in this case a porous primary coating into which the infiltrant metal flows by exfilt'ration from the skeleton during the subsequent infiltration process. Since the infiltrant phase is substantially common to both the skeleton body and the finally produced coating, a dense metallurgical' bond is assured. a t Nickel has been found very satisfactory as the primary coating material. Finely divided nickel powder, preferably 'finer than 140 mesh size (U.S. standard), suspended in a liquid varnish or resin binder, has proven particularly successful as a primary coat former. When employing metal powders generally as the primary coat, substantially all of the powder should preferably range in size from about minus to plus 325 mesh. After thecoating is formed on a skeleton body by painting, dipping or spraying, and the resin cured by heating to an elevated 'curing temperature, the coated body is then subjected to an infiltration cycle during which the binder is volatilized and driven off. 'If the resin has a high vapor pressuredeleterious to the infiltrationfcycle, the volatilizationis then eflected prior to infiltration under substantially inert conditions while the composite skeletonisiembedded in the refractory ,powder pack.

If-desired, the nickel primary coat maybe produced by spraying using a metallizing gun and nickel wire as the material source, I re insure someadherence of the coating. to the skeleton, the surface of the skeleton is treated with a phenolic resin solution of medium viscosity (e.g. phenol formaldehyde) the excessLofwhichis wiped ofiand the material remaining on the surface and in the surface pores then cured at a temperature of about 350 F. The surface is lightly sand-blasted and then followed by spraying of the nickel to produce a primary coating which adheres to the resin treated surface As I before the resin is removed by volatilization either durplied a primary coating comprising bonded nickel powder shown in Fig. 1D. The skeleton with primary coat isv inserted in a refractory oxide powder pack in the mold shown in Fig 1E as comprising in cross section a graphite flask} against which is supported powder pack 3 which in 'turn supports the composite skeleton comprising ti- 'tanium carbide with primary nickel coat 1. Thetop. root portion 4 of the blade skeleton is left uncoated and has applied to it infiltrant metal 5 plus sufficient excess ready for infiltration into the pores of the skeleton and exfiltration from' the surface of the skeleton into the primary coating to form the final dense coating 6 shown in Fig. 1F.

he: bo nda y nd t ons te a l bet n t e @91 1 surface, the primary coating, and the skeleton, is illustrated by the expanded cross-sectional representation of Fig. 2 which shows the flask portion 2a, a packing of refractory oxide 3;; adjacent it supporting the composite skeleton comprising a porous foundation layer of nickel primary coating 1;: adhering to'the" porous skeleton portion 7 of titanium carbide. Fig. 3 is the same as Fig. 2 except that it shows the infiltration metal 8 in skeleton body 7. and also in primary coat 1c after exfiltration from the skeleton into the voids of the primary coatingat the instantbefore the, infiltrant has completely combined and alloyed with the material of the primary coating.

It will be appreciated that at this point of. the infiltration a concentration gradient will exist in the infiltrant, the infiltrant 8 surrounding the titanium carbide particles 7 being slightly enriched in titanium carbide due to the rounding ofi of the particles, and the infiltrant surround ing the partially dissolved primary coat 1a being enriched in ni kel- Qt Q set e i filt n i hqm enized te u the s a ns sul in n. ompl l ion ft e.

primary co a sho n, Fi

Fi 4 whic s a n escm ti 9 a nhq omi m rap is theactual appearance of the boundary conditions after. complete infiltration and exiiltration has occurred with complete alloying of thefinfiltrantwith thecoating reuit a bs a ti y o o ene m t x s u tur on ainin me p ecip tated t tan mrarb de own.

by a transversesection through the base surface and the finally produced coating. the relatively sharp line of demarcation resulting from this method of coating thus showing that the originalv surface vof.the carbide is not disrupted to any significant degree.

As illustrative of the invention, thefollowing examples aregiven;

' Example 1 A-suspens oa o 2 r ins f, a b nyl c e p wde of 400 mesh size. (U.S.. standard). in cubic centi meters of a cementing solution comprising a natural resin dissolved in a chlorinated solvent (of the type sold The figure also illustrates-.

by the Wall Colmonoy Company under the trademark Nicrobraz is employed in producing a primary coating on a sintered porous body of titanium carbide (60% dense) of approximately 0.2 inch square and 2 inches long. A layer of about 0.01 inch of the nickel was applied to the surface of the bar leaving one end face of the bar uncoated for receiving the infiltrant metal. After the coating hardened the resulting composite skeleton was packed in a ceramic powder pack, e.g. thoria, in the manner shown in Fig. 1E. A given amount of a heat-resistant nickel-base infiltrant alloy including an excess for exfiltration purposes (about nickel to 20% chromium), was placed on top of the uncoated end face of the, skeleton and the whole subjected to infiltration at above the melting point of the alloy but below the melting point ofthe nickel primary coating. The alloy had a melting point of slightly more than 50 C. below that of nickel. The infiltration was carriedout at a subatmospheric pressure of about 5 microns in an induction furnace to the point of completion of exfiltration. Photomicrographs of a mounted section similar to Fig. 4 indicated that the interface between the body and the coating was entirely sound and that substantially no deformation of the original skeleton occurred, that is a relatively sharp boundary line between the carbide base material and the coating was maintained, v Impact resistance of the coated specimen ranged from 7. to 9 inch-pounds based on an Izod drop impact test on a 3/ inch square cross section specimen.

, Examp A titaniumcarbide. skeleton body (about 60% dense) was produced measuring 0.17 by 0.17 inch square and approximately 2 inches long. 20-grams of relatively coarse nickel powderall passing through a mesh (U.S. standard) screen but remaining on a 325 'mesh screen suspended in 10' cubic centimeters of cementing solution comprising a; natural resin dissolved in a chlorinated solvent defined in Examplel was employed in producing the nickel coating. The coating thickness was about 0.03 inch over the surface of the bar with the exception of one end face which was used as the infiltrant contact face. After, the coating was. allowed to harden, the coated-skeleton. was packed in thoria powder with the uncoated end faceleft exposed to which was applied a heat-resisting nickel-base alloy comprising by weight about 13% to 16% chromium, about 6% to 8% iron, about 0.4 to 0.8 aluminum, about. 2.25 to 2.65% titanium, about 0.2 to 1.2% columbium, up to about 0.1% carbon, and the balancesubstantially nickel. The assembly was heated slowly at a subatmosphe'ric pressure of about 10 microns in an induction furnace to theinfiltration temperature during which time the residual binder in the primary coat was driven off leaving behind a partially sintered primary coat of nickel powder illustrated in i Fig. 2. The final infiltration temperature .was'above the infiltrantmelting point of about 14lQ C. but below the meltingpointof the nickel primary coat. The temperature was held for about 20 minutes at and near the 'mel ting point. The molten in'filtrant spread through the interconnectingpores of the skeleton by virtue of the capillary action thereof assisted by the force of gravity. The excess infiltrant exfiltrated from the surface of the carbide skeleton into the overlying primary coating and merged with it to form a dense coating of uniform alloy composition. Like Example 1, the photornicrograph showed a structure similar to that illustrated in Fig. 4, that is it revealed a substantially sharp boundary line between the carbide base material and the dense alloy coating.

Example 3 The procedure asoutline'd in Example 2 was followed except that another-type binding solution was employed informing thenickel' slurry. yThe 20 grams ofnickel powder was suspended in a solution ofcthyl; cellulose 1. await and acetone (solution prepared by dissolving one gram of ethyl cellulose in 10 cubic centimeters of acetone) and reach the temperature, at which temperature it was'held for an additional hour to insure'freeing the primary coat-- ing of the ethyl cellulose binder and to effect at least a partial sintering of the nickel powder. The coated skeleton was then furnace cooled under hydrogen to room temperature after which it was subjected to infiltration in accordance with the steps of Example 2. Y

Example. 4

A skeleton titanium carbide body, the same as that described in-Example 2, was coated with a 0.02 inch nickel layer by dipping the skeleton in'a medium viscosity phenolic resin' (heat setting type, e phenol-formaldehyde) and the excess wiped olf. The top face was left uncoated to provide contact with the infiltrant. The dipped skeleton was cured for 20 minutes atabout 250 F. (177 C.) to harden the coating. The body was'cooled and then sand blasted at about 25 pounds per square inch air pressure using 60'mesh al uminu'm' oxide abrasive and then followed by spraying using'a Brown and Sharpe gauge nickel wire and a Metco 4E gun manufactured by the Metallizing Engineering Company, the bar being rotated in a lathe during spraying. Ihe spraying was started at a distance of 15 to 18 inches, and after'acontinuous coat was applied, the nozzle of the "gun was brought to within 10 inches of the specimen for'the balance of the spraying.

The coated body wasthen infiltrated-as described in- ExampleZ with the-nickel-base alloy defined in said example. The microstructure of the final product was as sound as that illustrated by the photomicrograph of Fig. 4.

The impact strength of the bar, after grinding down to 0.19 by 0.19 inch square cross section (i.e. to a coating thickness of about 0.01 inch), was about 7.5 inch-pounds at room temperature and about 10 inch-poundsat 1800 F. (about 982 C.). The bar exhibited .thesame impact value even after heating for 2-4 hours in still air at Example 5 In producing an airfoil-like shape having approximate dimensions of about 4 inches long, 2'inches wide, and a employed. Thus, in. preparinga primary coat of about 0.01 inch on all airfoil surfaces, the same suspension of nickel powder in the cementing solution is used, an end face of the airfoil being left uncoated to receive infiltrant metal-Q Thereafter, the prepared airfoil section'is infiltrated in the same manner as the method described in Example 2. p v

'As has been indicated hereinbefore, the method of the invention as described in Examples 1 to 2, and in particular in Example 5, is especially adapted to the coating of tapered bodiesysuch'as turbine buckets, diaphragm nozzles and varies, and other fluid guiding members characteri'zed 'by a relatively thick section tapering smoothly and 'arcuately into relatively thin edges. In utilizing the foregoing methods in the production'of a' turbine bucket, the steps outlined in the flow sheet of Figs. 1A to IP would be employed.

'Besides nickel, other metals may be employed in producing aprimary coating, provided these metals are compatible with the infiltrant r'netalarid alloy with it in pro.- ducing the desired coatingij such other metals may include cobalt, iroin. chromium, tungsten, molybdenum,

tantalum, ,niobium,"or any other metal, or mixture, or'

alloy of these metals, upon which the infiltrant alloy may be based, provided the metal oralloy has a higher melting point than the 'infiltrant.

The porous skeleton of refractory metal compound on which theprimary. coating is formed may'be produced in accordance with the method outlined in copending application U .S'. Serial No. 442,564, filed July 12, 1954, now U.S..'Patent No. 2,752,666, inrthe names of Claus G. Goetzel and John -B. Adamec, also assigned to the present assignee. According to this copending application, in producing refractory carbide skeletons or refractory compound skeletons having intercommunicating pores,'hot or cold pressingmay be employed. It is preferred that these 7 materials, prior to pressing, be mixed with a binder metal in amounts up to 15% for example such binder metals as iron, nickel, cobalt, etc. I p s I I-f the powdermixture is cold-pressed into a porous 1 body, it-is given a pre-s'intering treatment in a reducing atmosphere of ordinary or sub-atmospheric pressure below I 25.00 microns ofr'mercury column,kpreferably at a te'r'n-' sintering treatment is not required provided the hot pressing temperature is above the liquefaction, temperature of the cementing component. 1 After'the skeleton body is produced'it may be machined to a size close torthe final specifications if necessary, by cutting with cemented carbide tools, orby refractory wheel grinding, diamond chipping, orother methods commonly employedin thefabrication of'hard carbideproducts." In machining the body,

an over-size shrinkage allowance of about 2% to 10% is generally made, in order to compensate for the shrinkage which occurs in subsequent heating operations.

Final coating thickness ofthe infiltrated article may range from one-thousandth toone-sixteenth .of an inch, preferably from five-thousandths to'thirty-thousandths,

' The thus preparedskeleton body is'thensubjected to a high temperature sintering treatment in order to effect additional bonding of the carbide particles'into 'a porous skeleton 'of sufficient strength to enable the body to retain'its shape during subsequent infiltration treatment.

In carrying out thehigh temperature sintering operation,

it is preferred so 'sinterthe skeleton bodyat -a tempera- ,ture between, 50 C. and 250 CL above the temperature;

used inthe subsequent infiltration operation in a technical vacuum corresponding to a sub-atmospheric pressure rang ing froman initial pressure'of preferably notrmore than microns down to a final or, finishing pressure of 50 microns, of mercury and'preferably downto 10 microns. The surrounding gas at such subatrnospheric pressure must be non-oxidizing to the body, i.e. .reducing or inert,'tol

borides, nitrides, silicid es, etc., of titanium, zirconium,

chromium, molybdenum,tungsten, vanadium, columbinm, tantalum, etc., and mixtures of two or more of these compounds. or the refractory compoundirnay' also include.

such refractory oxidesas'oxi'des of aluminum, beryllium,

zirconium, thorium, magnesium,c erium etc: Theinvention ispreferably applicableto refractory metal carbides,

s particularly titanium carbide, or a carbide, based on titanium. Thus, titanium-base carbide may comprise up to about by volume of each of such metal carbides,

as silicon carbide, boron carbide, and up to about by volume each of chromium carbide, columbium carbide, tungsten carbide, zirconium carbide, or hafnium carbide, the total amounts'of these carbides generally not exceeding 25% by volume ofthe titanium-base carbide. By titanium-base carbide is meant a carbide comprising substantially titanium carbide.

The matrix-forming metals which may be employed in the metalliferous systems referred to herein include the iron group metals iron, nickel and; cobalt, rr'iixturesthereof, and heat-resistant alloys based on these metals,-i.e. heat resistant nickel-base, cobalt-base and iron base.

Examples of nickel-base, matrix-forming alloys include; 80% nickel and 20% chromium; 80% nickel, 14% chromium and 6% iron; chromium, 7% iron, 1% niobium, 2.5% titanium, 0.7% aluminum and the balance nickel; 58% nickel, 15% chromium, 17% molybdenum, 5% tungsten and 5% iron; 95% nickel, 4.5% aluminum and 0.5% manganese, etc. 1

Examples of cobalt-base alloys which may. be employed as matrix-forming metals include: 69% cobalt, 25 chromium, and 6% molybdenum; 65% cobalt, 25 chromium, 6% tungsten, 2% nickel, 1% iron and other elements making up the balance of 1%; 56% cobalt, 10% nickel, 26% chromium, and 7.5% tungsten, and some carbon; and 51.5% cobalt, 10% nickel, chromium, 15% tungsten, 2% iron, and 1.5% manganese, etc.

Some of the iron-base matrix-forming alloys include: 53% iron, nickel, 16% chromium, and 6% molyb denum; 74% iron, 18%. chromium and 8% nickel; 86% iron and 14% chromium; 82% iron and 18% chromium; 73% iron and 27% chromium, etc.

The matrix-forming infiltrant metal or alloy may contain up to about by weight of a metal selected from the group consisting of chromium, molybdenum and tungsten, the sum of the metals of said group preferably not exceeding 40%, substantially the. balance being at least one iron group metal selected from the group consisting of iron, cobalt and nickel, the sum of the iron group metals being'preferably at least about 40% by weight of the matrix-forming alloy. If desired, the matrixfonning allo'y may also contain up to about 8% total of at least one metal from the group columbium, tantalum, and vanadium.

Alloys of the aforementioned types containing effective amounts of so-called well-known strengthening or agehardening elements, such as zirconium, titanium, aluminum, etc., may also be employed in matrix-forming metals or alloys.

'Metalliferous systems based on refractory metal compounds (e.g. titanium-base carbide) and matrix-forming metals, may be produced over a wide range of compositions. In producing bodies by liquid phase sintering or by infiltration, the refractory metal compound may range from about 40% to 80% by volume (preferably about 45% to 75%) and the matrix-forming metal range from about 60% to 20% by volume (preferably about 55% to 25% It will be appreciated that the present invention is also applicable to the production of cladded products generally, for example, to the production of cladded plates or other shapes of refractory carbide, or of other refractory compound material, wherein at least one side is cladded. The invention may be utilized in the production of brazeable cladded surfaces for use as mold liners in brick molds and other similar wear-resisting applications. Or, if desired, the invention may be employed in producing laminated structures comprising a series of alternate layers of a hard refractory compound and substantially ductile metal. In this case the laminated product would be produced from a laminated composite skeleton comprising,

for example, sintered, porous, layers of titanium carbide alternating with sinteredporous layers of the primary metal coating. Upon infiltration, the pores of the carbide and the alternate layers of primary coating would absorb the. infiltrant metal to form a solid laminated product,

The expressions coat, coating, clad, cladding, etc.,'as employed herein are meant to include thelayer of one material ontop of another, or a layer of, material between two other layers. The expression .composite skeleton is meant to designate a porous skeleton body of refractory compound material having adhering to it a primary metal coating.

While. the present invention has been described as a process for producing coated or cladded composites, it will be appreciated it also provides a combined infiltration and cladding mold assembly for carrying out saidprocess. Thus, an infiltration mold assembly is providedcomprising means for confining a powder pack of refractory oxide in which is supported snugly an infiltratable c0mposite skeleton body, the skeleton having on at least one surface thereof or between two surfaces a foundation metallayer or primary metal coating of predetermined thickness.

In cross-section such a mold assembly may define at one side thereof an inner confining wall (efg. graphite) against which is packed refractory oxide powder (e.g. zirconia or thoria) which in turn is packed snugly against a composite'skeleton comprising a primary metal coating on a surface comprised substantially of a refractory metal compound (e.g. titanium carbide) which may or may not alternate with the primary metal coating.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims. 4

We claim:

1. A method for simultaneously: infiltrating and coat ing a porous refractory body which comprises producing a coherent porous skeletonof desired shape comprising a high melting point refractory compound material adapted for infiltration with a matrix-forming metal, providing the surface of said skeleton with a primary coating of metal of predetermined thickness, said metal having a melting point higher than the matrix-forming metal subsequently contained in the pores of said skeleton, adequately supporting the;coated surface of said skeleton in a pack of substantially inert refractory oxide material leaving a portion exposed for receiving infiltrant metal,

posed portion with said matrix-forming metal at a temperature below the melting point of the primary metal coating, and continuing said infiltration in said skeleton body whereby excess matrix-forming metal exfiltrates through the coated surface thereof and into the overlying metal coating and merges therewith by alloying.

2. A method for simultaneously infiltrating and coating a porous refractory body which comprises producing a coherent porous skeleton of desired shape comprising a high melting point refractory compound material adapted for infiltration with a matrix-forming metal, providing the surface of said skeleton with a substantially adherent primary coating of metal in particulate form of predetermined thickness, said metal having a melting point at least 50 C. higher than the matrix-forming metal subsequently contained in the pores of said skeleton, ardequately supporting the coated surface of said skeleton in a bed of substantially inert refractory oxide material leaving a portion exposed for receiving infiltrant metal, subjecting said coated skeleton to infiltration at the exposed portion with said matrix-forming metal at a temperature below the melting point of the primary metal coating,

11 and continuing said infiltrationwhereby excess matrixforming metal exfiltrates through the surface thereof and into the overlyingp'rimary metallcoating and merges therewith.

3.- The method of claim 2wherein the primary metal coating in particulate form is applied by metal spraying. 4. The method of claim'2 wherein the primary metal coating in particulate form. is derived from a suspension of metal powder in a liquid binder solution. 1 i

5. The method of claim 4 wherein the metal powder suspension ranges in mesh size from minus 140 to plus 325. 1

6. A methodfor simultaneously infiltrating and coating a porous refractory bodywhich comprises producing a coherent porous skeleton'of desired shape comprising a high melting point refractory compound material adapted for infiltration with a matrix-forming metal, providing the surface of said skeleton with a primary coating of metal powder of predetermined thickness bonded together with a vaporizable binder, said metal having a melting point at least 50? :C. higher'than the matrix-forming metal subsequently contained in the pores of said skeleton,'adequately supporting the surface of said coatedskeletonin a bed of substantially inert refractory oxide powder leaving a portion exposed for receiving infiltrant metal, subjecting said coated. skeleton to heating to vaporize said binder, infiltrating said' coated skeleton with said infiltrant metal, and continuing said infiltration whereby excess matrixforming metal exfiltrates through the surface of said skeleton and into the overlying metal coating and merges and alloys therewith.

' 7 A method for simultaneously infiltrating and coating a porous refractory body which comprises producing a coherent porous skeleton of desired shape comprising a high melting point refractory compound material adapted for infiltration with a matrix-forming metal, providing the, surface pores of said skeleton with a heat curable resin, curing said resin in said pores, spraying said surface with a metal layer of predetermined thickness, said metal having a melting point at least 50 C. higher than the matrix forming metal subsequently con-.

tained in the pores of said skeleton, adequately sup porting the surface ofsaid coated skeleton 'in a bed. of substantially inert refractory oxide powder leaving a portion exposed for receiving infiltrant metal, subjecting said coated skeleton to heating to vaporize said. binder, infiltratingsaid coated skeleton with said matrix-forming metal, and continuing said infiltration whereby excess matrix-forming metal exfiltrates through thesurface of said skeleton and into the overlying metal coating and merges and alloys therewith. 7 v

8. An infiltration and cladding mold assembly comprising a mold having'confined thereina powder pack substantially inert refractory oxide material, a com.-

posite porous skeletonbody having ,a primary metal coat? ing of predeterminedfthickness .onfa't least one surface thereofand supported by saidpowderpack 'at least adjacent said =coated surface, and means associated with one end of said skeleton for'receiving infiltrant metal.

9. An infiltration and cladding mold assembly comprising a mold having confined therein a powder pack of substantially inert refractory oxide material, a composite porous skeleton body having a primary metal coating of predetermined thickness on at least one surface thereof and supported by said powder pack at least adjacent said coated surface and means associated with one end of said skeleton for receiving infiltrant metal, theprimary coat ing having a melting point higher than the infiltrant metal.

10. An infiltration and cladding mold assembly comprising a mold having confined therein a powder packof substantially inert refractory. oxide material, a composite porous skeleton body having a porous primary metal coating of predetermined thickness covering the surface thereof and supported by said powder pack surrounding snugly said coated surface and means associated with one end of said skeleton for receiving infiltrant metal, the primary metalrcoating having a melting point at least 50 C. higher than the infiltrant metal.

11. An infiltration and cladding mold assembly comprising a mold having confined therein a powder pack of substantially inert refractory oxide material, a composite porous skeleton body having a porous primary metal coating of predetermined thickness covering the surface thereof and supported ,by saidpowder pack surrounding snugly saidcoated surface, the primary metal coating comprising particles of metal ranging in size 'substantially from minus 140 mesh to 'plus 325 mesh, and means associated with one end of said skeleton'for receiving infiltrant metal, the primary-metal coating having a melting point at least C. higher than'the infiltrant metal. i

References Cited in the file of this patent UNITED STATES PATENTS 7 2,119,989 Higgins June 7, 1938 2,325,553 Schleicher a July- 27, 1943 2,667,427 Nolte Jan. 26,1954 2,719,095 Scanlon Sept. 27, 1955 2,733,167 Stookey Jan. 31, 1956 2,751,293 Haller June 19, 1956 2,768,099 Hoyer Oct. 23, 1956 2,769,611 Schwarzkopf Nov. 6, 1956 2,798,577 .La Forge July 9, 1957 FOREIGN PATENTS 661,031 Great Britain Nov. 14, 1951

Claims (1)

1. A METHOD FOR SIMULTANEOUSLY INFILTRATING AND COATING A POROUS REFRACTORY BODY WHICH COMPRISES PRODUCING A COHERENT POROUS SKELETON OF DESIRED SHAPE COMPRISING A HIGH MELTING POINT REFRACTORY COMPOUND MATERIAL ADAPTED FOR INFILTRATION WITH A MATRIX-FORMING METAL, PROVIDING THE SURFACE OF SAID SKELETON WITH A PRIMARY COATING OF METAL OF PREDETERMINED THICKNESS, SAID METAL HAVING A MELTING POINT HIGHER THAN THE MATRIX-FORMING METAL SUBSEQUENTLY CONTAINED IN THE PORES OF SAID SKELETON, ADEQUATELY SUPPORTING THE COATED SURFACE OF SAID SKELETON IN A PACK OF SUBSTANTIALLY INERT REFRACTORY OXIDE MATERIAL LEAVING A PORTION EXPOSED FOR RECEIVING INFILTRANT METAL, SUBJECTING SAID COATED SKELETON TO INFILTRATION AT THE EXPOSED PORTION WITH SAID MATRIX-FORMING METAL AT A TEMPERATURE BELOW THE MELTING POINT OF THE PRIMARY METAL COATING, AND CONTINUING SAID INFILTRATION IN SAID SKELETON BODY WHEREBY EXCESS MATRIX-FORMING METAL EXFILTRATES THROUGH THE COATED SURFACE THEREOF AND INTO THE OVERLYING METAL COATING AND MERGES THEREWITH BY ALLOYING.

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