US2683305A - Molybdenum coated article and method of making - Google Patents

Description

y 1954 c. G. GOETZEL 2,683,305

MOLYBDENUM COATED ARTIQLE AND METHOD OF MAKING Filed July 15, 1949 INVENTOR. A2 41/5 5 501-7254 Wyzw/ HTTDR'NEYS Patented July 13, 1954 UNITED STATES PATENT OFFICE MOLYBDENUM COATED ARTICLE AND METHOD OF MAKING Application July 15, 1949, Serial No. 105,035

6 Claims. 1

This invention relates to protective surfaces for structural components useful under high temperature and corrosive atmosphere conditions and particularly to protective surfaces or casings for the refractory metal molybdenum, the protective surface casings being integrally fused and diffused with the base substance.

Components suitable for use as buckets, blades, valves, nozzles, and the like, in gas or steam turbines, jet engines and devices having similar temperature and atmosphere conditions present problems difficult to solve. Such components must have certain desirable physical characteristics so that they will withstand the stresses involved and yet will not deteriorate under oxidizing or corrosive conditions. The elements must have high hot tensile strength, hot fatigue strength, and high resistance to creep at elevated temperatures.

Molybdenum possesses certain desirable characteristics which make it adaptable for structural materials exposed to high temperatures. Molybdenum in contrast to some other of the refractory metals is not very much heavier than certain of the alloy steels, nickel base alloys or cobalt base alloys, the specific gravity of molybdenum being 11.2. Because of its high fusion and evaporation temperatures, molybdenum has a very high modulus of elasticity which is in the order of 50,000,000

pounds per square inch. This indicates a high resistance to deformation and creep at very high temperatures. Also, the strength of molybdenum is high, particularly if in the wrought condition. For wire and sheet materials, a tensile strength of 90,000 pounds per square inch at 1100 F., and

37,000 pounds per square inch at 2000" F. is attainable. V In order to utilize these desirable physical properties, it is necessary to preserve the fine grain structure of the highly worked molybdenum metal. It also is important in subsequent treatments applied to the metal, not to overheat beyond about 2200 F., because in high purity molybdenum, such will cause excessive recrystallization and grain growth.

Molybdenum is abundantly found in the United States and its mining processes, metallurgy, physical metallurgy and metal working practices have been perfected. Further, the production of molybdenum products by powder metallurgy techniques, and also lately by casting techniques, has been perfected so that large ingots and shapes up to 250 pounds and sizes up to 7" in diameter and30" in length can now be produced.

One of the biggest difliculties has been that molybdenum is increasingly susceptible to oxidation at temperatures above 1100 F. This is because the reaction of molybdenum with oxygen results in the formation of molybdenum trioxide which becomes highly volatile at temperatures above 1650" F. Because of this, when the metal is exposed to temperatures of 1650 F. and higher, a rapid thermal decomposition will take place and the metal will be destroyed by the attack of oxygen. The attack will progress from the periphery to the core of the exposed body.

Because of this problem, it has been recognized that unless a protective atmosphere or vacuum is provided, such as in incandescent lamps or X-ray tubes, access of oxygen to the surface of the molybdenum must be prevented by employing physical or physico-chemical means which will permit retention of the metallic structure of molybdenum up to the temperature limits set by the aforementioned recrystallization and grain growth.

Surface protection has been attempted by conventional means such as by enveloping the metal in a stable ceramic, such as Silimanite or alumina, in the form of shells, tubes, etc. Spraying of the ceramic material in the form of a slurry and subsequently baking also was tried as well as slip-casting various washes of ceramic compositions differing in thermal expansivity and cementing properties. Other physical processes have been tried such as the surface deposition of metallic, semi-metallic or metalloidal substances onto molybdenum by such chemical treatments as precipitation or reaction displacement methods from suitable salts, these processes being carried out at ordinary temperatures or elevated temperatures. Electro-deposition, deposition from the vapor phase, or thermal decomposition from certain compounds also have beentried. In the coating processes just mentioned, the surfacing or casing did not achieve lasting results.

Molybdenum metal regardless of its comparatively large atomic radius and high heat of reaction due to its high melting point has a high coefiicient of diffusion at elevated temperatures and molybdenum for this reason penetrates at an increasingly rapid rate with rising temperature into other high melting metals as well as into alloys or compounds. Stable compounds such as the refractory oxides A1202, S102 or MgO when brought into contact with molybdenum metal at high temperatures are penetrated by the molybdenum. It can be theorized that place exchange reactions occur so that the molybdenum atoms switch positions with aluminum, silicon, or magnesium in the compounds and that complex compounds of the type containing the elements molybdenum and/or molybdenum oxide comsilicon, oxygen; or molybdenum, magnesium, oxygen are formed. There is a possibility that molybdenum atoms migrate through a grain boundary until they reach exposed surfaces. It also is possible that the stable oxides are locally reduced by the molybdenum and that the resulting molybdenum trioxide because of its very high vapor pressure penetrates through the crystal structure or the boundary regions of the stable compound. In any event, the penetration of the molybdenum and/or molybdenum oxide, compounds result in exposure to erosion and corrosion of the protective stable oxide surfaces.

One of the objects of this invention is the protection of molybdenum by utilizing a surfacing or casing method which provides for the protection (physically, chemically and metallurgically) of the molybdenum base metal, said surfacing or casing method also protecting the molybdenum against deterioration.

In one aspect of the invention, intermediary layers are placed between the molybdenum base and the corrosion resistant surface casing. The proper selection of the intermediate layer will enable formation of intermetallic compounds with the molybdenum, these compounds constituting the necessary barriers respective to diff-tbsion of the molybdenum into the surface casing and the surface metal into the molybdenum base. This is based on the fundamental difiusion laws which hold that diffusion rates are retarded inthe presence of compounds so that migration of the molybdenum through a barrier of molybdenum containing intermeta'llic compounds will be slowed down. If, however, the compound functioning as a diffusion barrier is not of the intermetallic type, such as the system molybdenumiron or molybdenum-nickel, but is of a nonmetallic type, such as a carbide, boride, silicide, etc., either of molybdenum or even better of .a foreign metal or non-metal, outward diffusion of molybdenum will be further inhibited.

It is a further object of the invention to produce synthetically, an intermediate layer in such a way as to offer one or, if possible, several suecessive continuous layers functioning as moderators or slow-down agents for the migrating molybdenum atoms, thus providing a casing for a molybdenum base metal which will be stable for long periods of time under high temperature oxidizing atmospheres.

By introducing soft and plastic metal layers,

between the non-metallic compound barrier layers, stress concentrations due to differences in expansivity or externally caused stresses, such as centrifugal forces, dynamic loads, etc, are relieved or eliminated.

These and other objects, advantages and features of the invention will become apparent from the following description and drawings.

Figure l diagrammatically illustrates one form of the invention.

Figure 2 diagrammatically illustrates another form of the invention,

Figure 3 illustrates one type of apparatus which may be used for coatin molybdenum sheet.

Figure 4 represents another type of apparatus which can be used for coating molybdenum sheet.

Figure 5 is an enlarged view of molybdenum sheet showing one manner in which the edges can be covered.

In one form of the invention, an intermediate layer of an iron-nickel alloy containing between 36% and 50% nickel can be used. The nickel, iron, or similar alloy layer can be produced on the molybdenum base in various manners such as by electro-deposition, spray coating or by the carbonyl process.

The pure metals iron, nickel, or cobalt; binary alloys of iron and nickel, iron and cobaltor nickel and cobalt; ternary alloys of iron, nickel and eobalt can be electro-deposited in a conventional manner in any desired ratio onto the finished molybdenum body. In case of an alloy, the deposit may either be of a homogeneous type, solid solutions for most ratios, or it may be deposited in individual successive layers or zones. The 'electro-deposit is then diffused and merged with the molybdenum base part by a subsequent heat treatment under protective atmospheres. Due to the comparative stability of electro-deposits, temperatures of a high order and prolonged times are required for the diffusion processes.

The pure metals iron, nickel and cobalt; the binary alloys of iron with nickel, iron with cobalt and nickel with cobalt; and the ternary alloys of iron, nickel and cobalt in any desired proportion can be applied to the molybdenum base by conventional spray methods. For this purpose, the metal or alloy can be employed in wire form or as an alloyed and disintegrated powder. Also, the metals can be deposited in indivilual layers and their diffusion controlled in the subsequent treatment to give the desired concentration :zones for adequate matching of their-expansivity with that of the base metal .or the ultimate surface material. Due to the history of such spray coating-s, which in general employ slightly oxidizing conditions, an intensive reduction and dillusion treatment is required for perfect bonding and merging of the deposit with the molybdenum base metal.

The metals iron, nickel and cobalt; the binary alloys between iron and nickel, iron and cobalt, nickel and cobalt; and the ternary alloys of iron, nickel and cobalt; and also binary, ternary or quaternary alloys of the metals iron, nickel and cobalt, respectively, with. molybdenum, the latter preferably in minor proportion, can be deposited on the molybdenum base by the thermal decomposition of the respective metal carbonyls. This method, employing the formation of the simple or multiple carbonyl compounds by the well-known process of combining the metal or alloy in question with carbon monoxide into the liquid compounds with the aid of high pressure (up to 2000 atms.) and a slightly elevated temperature (about ZOO-400 F), followed by a decomposition of the complex carbonyl compound at a somewhat higher temperature (about 600-800 F.) and ordinary pressures, is particularly suitable for the purpose of this invention. The deposits obtained, being either in form of a powder or of a sponge ones a coherent solid film or layer depending on the conditions prevailing in the decomposition chamber with the latter type of deposit obtainable whenthe mclyb denum part is suspended directly in the heat zone of the decomposition chamber, are highly reactive and known .to result in high .rates of diffusion at very low temperatures such as in the range of 1200-1650 F. It is this latter fact which is of particular importance, since it en ables diffusion bonding of the layer to the molybdenum at a temperature level which is safely below the one at which any significant changes in grain structure or physical properties could occur.

Thereafter an oxidationlproof and corrosion resistant surface casing can be placed on top of the intermediary alloy layers which is described. The preferred manner for deposition of the surface metal is by the vapor phase methods involving either pure metal or a compound of metal that termally decomposes upon deposition, initiating a metal atom exchange process. In the case of pure metals, chromium, silicon, zirconium, or aluminum, are the most desirable. Although pure chromium as surfacing casing is desirable for reasons of technical simplicity and economy of the process, the oxide of chromium (Cr O3) formed when exposing the metal to high temperature oxidizing atmospheres lacks some stability from a mechanical standpoint, and tends to mechanically disintegrate and flake and spall off, thus, constantly exposing fresh metal surfaces to the oxidizing atmosphere. This would eventually result in completely wearing through the chromium metal surface. Hence, metals giving more stable oxide films, such as zirconium, silicon, or aluminum are preferred for very high temperature application (above 2000 F.).

If the case formation process employs the previously mentioned mechanism of preferred decomposition of a compound, the halides of chromium, silicon, zirconium, or aluminum, such as chromous chloride, chromous iodide, silicon chloride, zirconium chloride, or aluminum chloride are suitable for the process.

Instead of the pure metals, it may be more advantageous and preferred to employ alloys of chromium with other metals mentioned which tend to form more stable complex oxides. Examples of alloys of chromium with elements to form a more stable oxide, are compounds of chromium with aluminum, with silicon, with zirconium, with aluminum and silicon, with aluminum and zirconium, or with aluminum, silicon and zirconium. In either case, double or triple halides, such as the chlorides, bromides or iodides of chromium plus aluminum, chromium plus silicon, chromium plus zirconium, chromium plus aluminum plus silicon, chromium plus aluminum plus zirconium, or chromium plus aluminum plus silicon plus zirconium, must then be employed.

Reference also may be made to applicants copending application, Serial No. 94,092, filed May 19, 1949 (now U. S. Patent No. 2,612,442), for details of the various manners of depositing the surface casing on the intermediate layers. The comparatively high degree of surface activity of the carbonyl type deposit is of great advantage in producing integral bonding, fusion and merger between the surface casing metals, alloys or compounds on the one hand and the intermediate layer and the base metal on the other. Thus, low temperatures and short times can be used for thedeposition, displacement and atom exchange processes underlying the oxidation proof case formation, which is of great ad-- vantage in view of the desirability to prevent heating the molybdenum base metal above its recrystallization. temperature.

In another aspect of the invention, the molybdenum base metal part can be carburized and then a soft metal introduced, such as iron, nickel or their alloys, by electroplating, spraying or carbonyl vapor deposition. The carburizing will result in a gradient of carbon concentration. Bonding then can be accomplished by appropriate diifusion treatment prior to application of the stable oxide surface casing. The bonding treatment subsequent to carburizing can, if necessary, be performed at a temperature above the melting point of the iron, nickel or alloy thereof. This will result in impregnating any pores produced during the carburizing of the molybdenum with the liquid metal or alloy, respectively.

Instead of the formation of carbides, etc., of molybdenum, similar compounds can be formed from other metals or non-metals, such as iron carbide or a complex carbide of iron and silicon, or nickel and silicon, or iron and boron, or nickel and boron. Conventional packs for gas carburizing methods can be used advantageously on iron or some of the other metal or alloy layers which have been deposited previously on or bonded with the molybdenum base metal surfaces. The aforementioned carbonyl vapor process has the advantage of suflicient flexibility to allow the deposition of successive layers of iron, iron carbide, nickel and the like, in any desired sequence and to any desired layer thickness in one operation. By varying the cycle with regard to temperature and time, it is possible to deposit a considerable number of alternate layers of the iron type metal and an alloy rich in iron carbide.

In the case of other barrier compound forming metals to be deposited as intermediate layers, silicon and aluminum are of particular significance since they are also'constituents of the complex ultimate surface casing, thus, functioning as diffusion and reaction moderators ahead of the reaction process involving the ultimate complex surfacing casing.

Aluminum deposits can be applied, either directly onto the molybdenum, or on an intermediate layer of iron, nickel, or nickel-iron alloy, by dipping the body into the liquid metal, into a suspension in a fused aluminum halide bath, or by placing into an enclosure in a calorizing powder pack. Silicon deposits likewise can be produced directly on the molybdenum, or the intermediate iron, nickel, or nickel-iron alloy layer. Pack siliconizing as well as thermal decomposition of silicon halides are suitable methods for application of silicon deposits. It also is possible to combine the above cited treatments with the aforementioned carburizing treatment, which is particularly advantageous in the case of siliconcarbon combinations which yield the very stable silicon carbide compound, a most effective inhibitor to diffusion of metals.

As previously mentioned, iron, nickel and ironnickel compounds can be deposited on the molybdenum base to form an intermediate barrier layer. as described.

Referring to Fig. 1, direct coverage of molybdenum is illustrated, the molybdenum base being indicated at it with a Type 1 layer ii thereon, said layer consisting of carbon, boron, aluminum, silicon, boron carbide, silicon carbide, and other metals and compounds combined with the molybdenum into complex compounds. Layer H is placed on the molybdenum in any of the manners previously described. The next layer 2, a Type II layer, may be of iron, nickel, or iron-nickel alloys as previously mentioned, of a type to diffuse into the compound of the first layer of material H or to alloy with molybdenum. The outer case or surfacing material it, Type III layer, may be chromium, silicon, or aluminum, or binary or ternary alloys thereof, bonding and conversion into stable complex oxide compounds being accomplished by diffusion treatment.

The outer casing is thereafter deposited An indirect coverage of molybdenum is seen in Figure. 2 wherein the molybdenum body is indicated at 1 2 having intermediate layers 15 and I5 (Type II). of iron, nickel, iron-nickel alloys, to diffuse or penetrate layer H or to alloy with the molybdenum. Layer H (Type I) may be carbon, boron, aluminum, silicon, boron carbide, silicon carbide, combined. with the molybdenum to form complex compounds. The outer casing I8 (Type III) may be chromium, silicon, aluminum, or binary or ternary alloys thereof.

The various layers may be formed or deposited as follows:

Type I 1. Carburizing:

a. gas carburizing 27. pack carburizi-ng 2. Al'uminizing:

a. liquid metal dip b. halide salt bath immersion c. halide gas decomposition 3'. Sili'conizing:

a. pack-impregnation b. halide gas decomposition Type II 1. Spraying 2'. Electroplating 3. Carbonyl process Type HI 1. Pack-impregnation 2. Halide gas decomposition 3. Halide salt bath immersion As an example of one method of surfacing molybdenum sheet with silicon carbide or boron carbide serving as the intermediate barrier layer against difiusion, reference may be made to Fig. 3 wherein the molybdenum sheet is indicated at Hi. The sheet preferably is shot-blasted in order to obtain a proper anchorage. The sheet is fed past a feed hopper 23 containing the carbide grains or a mixture of carbide grains and iron or molybdenum powder. The sheet is passed through a heating furnace 2! having a protective atmosphere, the temperature of said sheet being raised to 1296-1830 F. The sheet is then passed between two carbide rolls 22. In order to cover the other side of the sheet, it can be reversed and again passed through the apparatus.

Another manner in which the carbide can be placed on this sheet is illustrated in Figure. 4. wherein the shot-blasted molybdenum sheet 23, is passed through heating furnace :24, said, furnace being maintained with a protective atmosphere therein. Said sheet is heated to a temperature between 1299-1830" F. Spray guns 25 can be located on either side of the sheet for spraying hot SiC Or BiC particles with or without iron or molybdenum powder admixed as a binder.

Various methods can be used to insure that the edge is properly covered. For example, the strip 28 (Fig. 5) can have the carbide surface 2": formed thereon with upstanding portions 28, 28 which can be rolled over the edges to cover the same at 29', 28 to completely protect the sides of the sheet 25. Also, the edges of the sheet could be pointed so that the carbide surface would cover substantially the entire sheet face including the sloping face.

An example of one type of surfaced body is one wherein the molybdenum base is carburized by a gas carburizing proce. M020 being formed. Iron is then deposited on the carburized molybdenum base body by the carbonyl process and 8'. thereafter a. silicon-chromium. alloy is deposited on the iron layer by a pack-impregnation process.

Another example of the inventionis one wherein the molybenum base has iron. depositedthereon by the carbonyl process followed by carburizationof the iron layer to form FezC. The carburization iscarried out so that there is' a gradient of carbon concentration. Thereafter, another casing of iron is formedv by the carbonyl. process and a silicon-chromium outer casing integrally merged in a pack-impregnation procedure,

A third example is one wherein the molyb denum base is aluminized by a pack-impregnation deposition procedure. Following this, iron is deposited thereon by a carbonyl process and the iron carburized. Another layer of iron can be deposited by the carbonyl process, and a. siliconchromium-aluminum outer casing then intogrally merged with the body by means of a packimpregnation procedure and heat treatment.

A fourth example is one similar to the aforementioned third example with the exception that a casing of iron is integrally merged with the molybdenum base before deposition of aluminum.

A fifth example is one wherein the molybdenum base is siliconized by a pack-impregnation process and then has iron deposited thereon by means Of a. carbonyl process. Following. this, a siliconchromium casing is deposited by a. pack-impregnation technique and then integrally merged therewith.

A sixth example is one wherein the molybdenum bod has iron deposited thereon by means of the carbonyl process followed by siliconizing by pack-impregnation. Iron is then deposited thereon by the carbonyl process and thereafter the iron, is carburized by means of pack carburizing. A further coating of iron then is deposited thereon by a carbonyl technique. The outer casing of silicon-chromium then is placed thereon by pack-impregnation and. integrally merged with the body.

As a seventh example, the third example can have the coating of iron replaced with a. coating of iron-nickel with a nickel content. of 36-50%, said iron-nickel being deposited by a carbonyl process.

The eighth example is similar to the aforementioned sixth example, except that an iron-nickel allo is placed directly on the molybdenum before deposition of silicon thereon.

Pack-impregnation is. disclosed in applicants aforementioned co-pending application Serial No. 94,092 (now U. S. Patent No. 2,612,442). In general, pack-impregnationcan be carried out by placing the body in a pack composed of the pulverized material involved and passing a halide gas through the pack at the required high temperature. a

It is to be understood that variation may be made in the examples of techniques without departing from the spirit of the invention except as defined in theappended claims.

What is claimed is:

i. In a method of inhibiting the volatilization of molybdenum as molybdenum trioxide resulting from the reaction of a molybdenum-base body with oxygen-containing atmospheres at elevated temperatures, the improvement which comprises providing a coating of at least one intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof on the exposed surface of said molybdenum-base body, subjecting the thus-coated body. to heating in a non-oxidizing atmosphere at detail in an elevated temperature sufficient to integrally merge said layer to the molybdenum-base body by diffusion so as to form a barrier zone thereon with molybdenum, then surfacing said coated molybdenum-base body with at least one protective layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof and bonding said protective surface layer of metal to said intermediate barrier zone layer by diffusion heat treatment, whereby the intermediate barrier zone substantially inhibits the migration of atoms of molybdenum to the surface of the body and of atoms of the surface metal layer into the molybdenumbase body such that the attack of the molybdenum-base body by oxygen-containing atmosphere is greatly inhibited at elevated temperatures of about 1650 F. and higher. 7

2. In a method of producing components from a molybdenum-base body adapted to withstand corrosion at elevated temperatures and suitable for the production of buckets, blades, valves, nozzles, and the like, in gas turbines, steam turbines, jet engines and other devices employed under comparable temperature and atmospheric conditions, the steps comprising providing a coating of at least one intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof on the exposed surface of said molybdenum-base body, subjecting the thus-coated body to heating in a nonoxidizing atmosphere at an elevated temperature of at least about 1200 F. to integrally merge said layer by diffusion to the molybdenum-base body so as to form a barrier zone thereon with molybdenum, then surfacing said coated molybdenum-base body with at least one protective layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof and bonding said protective surface layer of metal to said intermediate layer by diffusion heat treatment, whereby the intermediate barrier zone substantially inhibits the migration of atoms of molybdenum to the surface of the body and atoms of the surface metal layer into the molybdenum-base body such that the protectively surfaced molybdenum-base body has substantially improved resistance to deterioration and to catastrophic oxidation at elevated temperatures of about 1650 F. and higher.

3. In a method of producing components from a molybdenum-base body adapted to withstand corrosion at elevated temperatures and suitable for the production of buckets, blades, valves, nozzles, and the like, in gas turbines, steam turbines, jet engines and other devices employed under comparable temperature and atmospheric conditions, the steps comprising providing a coating of at least one intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof on the exposed surface of said molydenum-base body, subjecting the thus-coated body to heating in a non-oxidizing atmosphere at an elevated temperature of at least about 1200 F. to integrally merge said layer by diffusion to the molydenumbase body so as to form a barrier zone thereon, then surfacing said coated molydenum-base body with a protective layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof by deposition from a vapor phase containing said metal and bonding said protective surface layer of metal to said intermediate layer by diffusion heat treatment, whereby the intermediate barrier zone substantially inhibits the migration of atoms of molybdenum to the surface of the body and atoms of the surface metal layer into the molydenumbase body such that the protectively surfaced molybdenum-base body has substantially improved resistance to deterioration and to catastrophic oxidation at elevated temperatures of about 1650 F. and higher.

4. In a method of producing buckets, blades, valves, nozzles, and the like, for use in gas turbines, steam turbines, jet engines and other devices employed under comparable temperature and atmospheric conditions from a molydenumbase body, the steps comprising forming a gaseous metal carbonyl phase containing a metal carbonyl selected from the group consisting of iron, nickel and cobalt carbonyl and mixtures thereof, bringing said metal carbonyl phase in contact with said molydenum-base body, decomposing said gaseous metal carbonyl phase at a temperature of about 600 F. to 800 F. and depositing a coating of at least one intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof on the exposed surface of said molybdenum-base body, subjecting the thus-coated body to heating in a non-oxidizing atmosphere at an elevated temperature of at least about 1200 F. to integrally merge said layer by diffusion to the molybdenumbase body so as to form a barrier zone thereon with molybdenum, then surfacing said coated molybdenum-base body with a protective layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof and bonding said protective surface layer of metal to said intermediate layer by diffusion heat treatment, whereby the intermediate barrier zone substantially inhibits the migration of atoms of molybdenum to the surface and atoms of the surface metal layer into the molybdenum-base body such that the protectively surfaced molydenum-base body has substantially improved resistance to deterioration and to catastrophic oxidation at elevated temperatures of about 1650 F. and higher.

5. In a method of producing buckets, blades, valves, nozzles, and the like for use in gas turbines, steam turbines, jet engines and other devices employed under comparable temperature and at mospheric conditions from a molybdenum-base body, the steps comprising forming a gaseous metal carbonyl phase containing a metal carbonyl selected from the group consisting of iron, nickel and cobalt carbonyl and mixtures thereof, bringing said metal carbonyl phase in contact with said molybdenum-base body, decomposing said gaseous metal carbonyl phase at a temperature of about 600 F. to 800 F. and depositing a coating of at least one intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof on the surface of said molybdenum-base body, subjecting the thus-coated body to heating in a non-oxidizing atmosphere at an elevated temperature of about 1200 F. to 1650 F. to integrally merge said layer by diffusion to the molybdenum-base body so as to form a barrier zone thereon with molybdenum, then surfacing said coated molybdenum-base body with a protective layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof by deposition from a vapor phase containing said metal and bonding said protective surface layer of metal to said intermediate layer by diffusion heat treatment, whereby the intermediate barrier zone substantially inhibits the migration of atoms of molybdenum to the surface and atoms of the surface metal layer into the molybdenum-base body such that the protectively surfaced molybdenum-base body has substantially improved resistance to deterioration and to catastrophic oxidation at elevated temperatures of about 1650 F. and higher.

6. A protectively surfaced molybdenum-base body having substantial resistance to catastrophic oxidation in oxygen-containing atmospheres at elevated temperatures which comprises a molybdenum-base portion, an intermediate layer of a metal selected from the group consisting of iron, nickel, cobalt and alloys thereof covering the exposed surface of said portion, said intermediate layer being merged integrally with said molybdenum-base surface and being characterized by a difiusion barrier zone containing molybdenum, and a surface layer of metal selected from the group consisting of chromium, silicon, aluminum, zirconium and alloys thereof covering said inter- 12 mediate layer and merged therevuth, whereby said body has improved resistance to oxidation at elevated temperatures of about 1650 F. and higher.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,650,979 Brace Nov. 29, 1927 1,718,563 Kelley June 25, 1929 1,899,569 Howe Feb. 28, 1933 2,096,924 Schwarzkopf m--- Oct. 26, 1937 2,109,485 Ihrig Mar. 1, 1938 2,304,297 Anton g Dec. 8, 1942 2,450,851 Colbert Oct. 5, 1948 2,450,855 Colbert Oct. 5, 1948 2,450,856 Colbert Oct. 5, 1948 2,475,601 Fink July 12, 1949 2,497,090 Miller Feb. 14, 1950

Claims (1)

1. 6. A PROTECTIVELY SURFACED MOLYBDENUM-BASE BODY HAVING SUBSTANTIAL RESISTANCE TO CATASTROPHIC OXIDATION IN OXYGEN-CONTAINING ATMOSPHERES AT ELEVATED TEMPERATURES WHICH COMPRISES A MOLYBDENUM-BASE PORTION, AN INTERMEDIATE LAYER OF A METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL, COBALT AND ALLOYS THEREOF COVERING THE EXPOSED SURFACE OF SAID PORTION, SAID INTERMEDIATE LAYER BEING MERGED INTERALLY WITH SAID MOLYBDENUM-BASE SURFACE AND BEING CHARRACTERIZED BY A DIFFUSION BARRIER ZONE CONTAINING MOLYBDENUM, AND A SURFACE LAYER OF METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, SILICON, ALLUMINUM, ZIRCONIUM AND ALLOYS THEREOF COVERING SAID INTERMEDIATE LAYER AND MERGED THEREWITH, WHEREBY SAID BODY IMPROVED RESISTANCE TO OXIDATION AT ELEVATED TEMPERATURE OF ABOUT 1650* F. AND HIGHER.

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