US3499740A - Oxidation resistant coated article containing iridium,ruthenium,molybdenum or tungsten - Google Patents

Description

March 10, 1970 D. w. RHYS 3,499,740

OXIDATION RESISTANT COATED ARTICLE CONTAINING IRIDIUM, RUTHENIUM. MOLYBDENUM OR TUNGSTEN Filed 001;. 24, 1966 6 Sheets-Sheet 1 3%NMAAAA7QA m /.200. c. GOLQ A/E/GHT PERCENT March 10, 1970 D. w. RHYS 3, ANT CO OXIDATION RESIST ATED ARTICLE CONTAINING IRIDIUM, RUTHENIUM, MOLYBDENUM OR TUNGSTEN Filed Oct. 24, 1966 6 Sheets-Sheet 2 agio x T a a 4 v y"; QV/AVAYA'A 1200 c. 601.4 A//6//7' PERCENT f0 3O 40 6O .90 /50c. G049 1/5/6197 PEfiCEA/T March 10, 1970 D. .RHYS 3,

OXIDAT RESISTANT ATED ARTICLE CONTAINING IRID M, RUTHENIUM, MOLYBDENUM OR TUN EN Filed Oct. 24, 1966 Sheets-Sheet /70 A9 a0 av no so 90 A200 c. G040, A/E/Gf/T PERCENT.

a 60 AVAY/I 50 a @W /O 2 0 3O 40 -50 6 O /450 2*. 00/. a, A/ /cv/r PERCENT D. w. RHYS 3,499,740 OXIDATION RESISTANT COATED ARTICLE CONTAINING March 10, 1970 IRIDIUM, RUTHENIUM, MOLYBDENUM OR TUNGSTEN Filed Oct. 24, 1966 6 Sheets-Sheet 4 3O /Z00 c. GOL 0 A/E/Gf/T PERCENT 604 4/00/17 PERCENT March 10, M70 D. w. RHYS 3,499,740

OXIDATION RESISTANT COATED ARTICLE CONTAINING IRIDIUM, RUTHENIUM, MOLYBDENUM 0R TUNGSTEN Filed Oct. 24, 1966 6 Sheets-Sheet 5 /Z00 C' 6040 A/E/GHT PEFC'E/VT D. w. RHYS 3,499,740 OXIDATION RESISTANT COATED ARTICLE CONTAINING March 10, 1970 IRIDIUM, RUTHENIUM, MOLYBDENUM OR TUNGSTEN 6 Sheets-Sheet 6 Filed Oct. 24, 1966 m m M 9 @i/ N a w w 7 A; 5 w w/ Z w C Kw 4? 0 United States Patent Int. Cl. B231) 3/00, 3/20, 3/10 US. (:1. 29-198 17 Claims ABSTRACT or THE DISCLOSURE Coated metal article has body and coating of different compositions which are resistant to interdiffusion at elevated temperatures and which are single-phase conjugate compositions falling at opposite terminals of an alloy tie line on a ternary metallurgical system diagram having gold at one apex, palladium or platinum at a second apex and ruthenium, iridium, tungsten or molybdenum at the third apex.

The present invention relates to coated metal articles and, more particularly, to coated metal articles for use at elevated temperatures.

It is well known that the elements ruthenium, iridium, tungsten and molybdenum are strong but readily oxidized at elevated temperatures and this behaviour is also generally characteristic of alloys rich in these elements. In particular when surfaces of articles that are made of or coated with these metals, i.e. elemental metals or alloy metals, are heated to elevated temperatures such as 900 C. and higher, volatile oxides readily form from the metals and the surfaces thereof lose weight at high rates which vary with the rate of air flow over the surfaces. The poor oxidation resistance of ruthenium, iridium, tungsten and molybdenum metals seriously limits the utility thereof. For instance, ruthenium and iridium have high strength above 900 C. and would be especially useful in the glass industry, particularly since ruthenium and iridium are not attacked by some reactive glasses that present serious corrosion problems.

It would be desirable to provide ruthenium, iridium, tungsten or molybdenum metals with thin oxidation-resistant coatings in order to be able to obtain more benefit from the strength and other desirable properties of these metals at elevated temperatures. However, heretofore, difficulties have arisen when attempts were made to protect a body of such metal by providing it with a coating of an oxidation-resistant metal, e.g. commercially pure platinum, due to diffusion of the body metal and the coating metal and the accompanying unsatisfactory result of rapid loss of oxidation resistance.

Although many attempts were made to overcome the foregoing difficulties and other difliculties and disadvantages, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that oxidation-resistant coated metal bodies that are also resistant to interdiffusion of the coating and body can be made of new combinations of metals.

It is an object of the present invention to provide an oxidation-resistant coated metal body that is resistant to interdiffusion of the coating metal and body metal at elevated temperatures.

Another object of the invention is to provide a method for providing a coated metal body having an oxidation resistant coating on a body of readily oxidizable metal.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which FIGURES 1 through 7 illustrate phase boundaries and tie lines in ternary metallurgical equilibrium systems as follows:

FIGURE 1 pertains to the ruthenium-palladium-gold system at 1200" C.;

FIGURE 2 comprises FIG. 2a and FIG. 2b which pertain to iridium-palladium-gold systems at equilibrium temperatures of 1200 C. and 1450" C. respectively;

FIGURE 3 comprises FIG. 3a and FIG. 3b which pertain to molybdenum-palladium-gold systems at equilibrium temperatures of 1200 C. and 1450 C. respectively;

FIGURE 4 comprises FIG. 4a and FIG. 4b which pertain to tungsten-palladium-gold systems at equilibrium temperatures of 1200 C. and 1450 C. respectively;

FIGURE 5 pertains to the ruthenium-platinum-gold system at 1100" C.;

FIGURE 6 pertains to the iridium-platinumgold system at 1200 C.; and

FIGURE 7 pertains to the tungsten-platinum-gold system at 1100 C.

Generally speaking, the present invention contemplates a coated metallic body comprising a metallic body which is readily oxidizable and a metallic coating of an oxidation resistant alloy wherein the metals and alloys are single-phase conjugate compositions at opposite ends of a tie line through a two-phase area of a ternary metallurgical system in equilibrium at an elevated temperature, the metals and the alloys each having a solidus temperature above the said elevated temperature, and are thus characterized by negligible or no solubility or difiusibility in each other at the said elevated temperature.

The alloys from which the body can be formed according to the invention are those of ruthenium with platinum or palladium, which can contain as little as about 5% ruthenium or any greater amount; those of iridium with platinum or palladium which can contain as little as about 5% iridium or any greater amount; and those of either tungsten or molybdenum with a small amount of palladium, say up to about 5%. All of these alloys which contain platinum may contain small additions of gold.

The alloys which can be used to coat the body consist of gold with either platinum or palladium and normally a third element, which is the strong but readily oxidizable element of the body and advantageously comprises at least 50% of the body.

While the terminal compositions for the metallic body and coating are variously referred to herein as essentially ternary alloys or as alloys containing specified amounts of one or two elements in a ternary system and the balance essentially the third element, it is to be understood that this does not exclude presence of small, non-detrimental amounts of other elements in the terminal alloys, in which instances the relative weight proportions of the terminal alloy elements are retained. (All alloy compositional percentages set forth herein are by weight.) For example, small additions of zirconium in the range 0.1% to 0.5% zirconium can be introduced in alloys of the iridium systems and small additions of rhenium in the range 0.1% to 2.0% rhenium can be made to alloys of the ruthenium systems referred to herein. Such additions will in many cases make the alloy a quarternary alloy.

In the ternary diagrams of the elements for the coated body, a line can be drawn as the boundary between single phase and two-phase alloys. The position of this line de pends upon the temperature, and in the present invention an important temperature is 1200 C., being that reached by articles in contact with molten glass.

In each of the ternary diagrams shown by FIGS. 1 through 7 the hatched area is that in which the alloys are single-phase and the plain area is that which includes twophase alloys. Some of the alloys to which the figures relate are three-phase, but the three-phase areas are not delineated in these figures inasmuch as they do not form part of the invention.

In each of FIGS. 1 through 7 a line shows the boundary between the single-phase and two-phase alloys, and on this line the compositions are those of the terminal solid solutions. It will be seen that in 'FIG. 1 the boundary line D is curved over part of its length and practically merges into the ruthenium and palladium axes of the diagram at about 22% ruthenium and about 50% palladium, respectively. In FIG. 2a, the boundary line B merges into the palladium axis at about 40% palladium and into the iridium axis at about 60% iridium, and in FIG. 2b the boundary line F merges into the palladium aXiS at about 30% palladium and into the iridium axis at about 70% iridium. In FIG. 3a the boundary line G practically merges into the palladium axis at about 8% palladium and into the molybdenum axis at about 31% molybdenum, and in FIG. 3b the boundary line H practically merges into the palladium axis at about 40% palladium and into the molybdenum axis at about 32% molybdenum. In FIG. 4a the boundary line I merges into the palladium axis at about palladium and into the tungsten axis at about 30% tungsten and in FIG. 4b the boundary line K practically merges into the palladium axis at about 40% palladium and into the tungsten axis at about 32% tungsten. In FIG. 5 the boundary line L practically merges into the platinum axis at about 70% platinum and into the ruthenium axis at about 35% ruthenium. In FIG. 6 the boundary line M practically merges into the platium axis at about 55% platinum and into the iridium axis at about 50% iridium. In FIG. 7 the bounudary line N practically merges into the platinum axis at about 70% platinum and into the tungsten axis at about 60% tungsten. It is to be understood that limited single-phase compositional areas are existent near ruthenium, iridium, tungsten, molybdenum and gold apexes of the ternary systems in the drawing, even though single-phase areas are not delineated by boundary curves at such places on the drawings due to the very small size of such solid solution areas. Thus, it is understood that both terminals of each tie line are at single-phase compositions.

Although ascertaining the exact shape of boundary curves in ternary systems involves considerable work, methods for ascertaining such curves are well known to those skilled in the metallurgical art. The boundary curves shown in FIGS. 1 through 7 are shown to illustrate the principles of the invention. Boundary curves for other systems in accordance with the invention can be determined by those skilled in the art.

A tie line, as used in this disclosure, means a line joining points on the curve or curves that represent the boundary line betwaeen a single phase and a two phase alloy region at the equilibrium temperature; the said two points represent compositions of two terminal solid solutions which will exist together in a two phase alloy and will not diffuse into one another at the equilibrium temperature.

In the invention, the body is made of a metal or an alloy of composition at or close to one end of the lie line and the coating is made of an alloy of composition at or close to the other end. In all the ternary alloy systems for the invention in question, the composition at one end of each tie line will be that of a relatively readily oxidizable metal or alloy and this is used for the body, the composition at the other end, i.e. the conjugate composition, will be that of an oxidation-resistant alloy for the coating.

To find an appropriate metal and alloy pair or pair of alloys for any given purpose is a fairly simple matter, even in the absence of a ternary diagram showing the boundary line containing the various terminal solid solutions at the temperature in question. In any two-phase alloy it is possible by inter ulia an electron probe microanalyser to determine the compositions of the two phases in it, and these will be the compositions of two alloys which will not interdiffuse. Thus, considering FIG. 1, an alloy containing for example 20% ruthenium, 60% palladium and 20% gold and therefore at the point A (where the 20% ruthenium, 60% palladium and 20% gold lines intersect) is found by the electron probe to contain two phases, one being of the composition 99% ruthenium and 1% palladium and the second being of the composition 73% palladium, 25% gold and 2% ruthenium. An alloy of the composition 99% ruthenium and 1% palladium lies on the practically merged line D at the point B, and an alloy of the composition 73% palladium, 25% gold and 2% ruthenium lies on the line D at the point C. The line Z joining the points A, B and C is the tie line of the phases and the compositions at B and C are conjugate compositions.

In carrying the invention into practice, it is advantageous that the metallic body and coating consist essentially of metals and alloys in one of the systems rutheniurn-palladium-gold, iridium-palladium-gold, tungsten-palladium-gold or molybdenum-palladium-gold. In advantageous metallic embodiments made according to data in these systems the coating alloy is a palladium-gold alloy and the body is of a ruthenium-rich, iridium-rich, tungsten-rich or molybdenum-rich tie line terminal composition in one of these systems. It will be noted that in the ternary diagrams provided herein for metallurgical systems with palladium and gold, the alloy tie lines generally fan out from the apexes at ruthenium, iridium, tungsten and molybdenum. Thus, these palladium-gold systems have tie line terminal compositions which are especially advantageous for protecting alloys which are rich in one of the readily oxidizable elements ruthenium, iridium, tungsten and molybdenum. Accordingly, palladium-gold tie line terminal composition coatings are especially useful for obtaining benefits of the high elevated temperature strength of the readily oxidizable elements, especially the high strength of iridium, tungsten and molybdenum. Where an alloy is referred to herein as being rich in a given element or as having a base of a given element, the alloy contains at least 50% of the given element.

The tie lines in the platinum-gold ternary systems illustrated by FIGS. 5, 6 and 7 generally fan out from the high gold apex of the diagrams and are thus in marked contradistinction to the alloy tie lines in the palladiumgold ternary systems illustrated herein. Since the platinumgold ternary alloy tie lines tend to converge near high gold alloys, and high gold alloys have low melting points, in many instances less than 1200 C. the platinum-gold systems are not advantageous for protecting bodies which are rich in the highly oxidizable elements and are needed for use at temperatures of 1200 C. and higher. It is to be appreciated that compositions at the ends of tie lines in the platinum-gold ternary systems can be used to protect platinum-rich alloys, particularly at temperatures up to 1100 C.

Inasmuch as it is well known that gold has a relatively low melting point, it will be understood that compositions of palladium-gold or platinum-gold alloys (including ternary alloys containing these elements) will be chosen so that the solidus temperature of the alloy is above the temperature of intended use. For instance, palladiumgold alloys for coatings on bodies for use at 1200 C. and higher will usually contain not more than about 40% gold.

For the purpose of giving those skilled in the art a better understanding of the invention and/ora better appreciation of the advantages of the invention the following illustrative examples are given.

An iridium-rich alloy of an iridium-palladium tie line terminal composition containing 1% palladium and balance essentially iridium was prepared by argon arc melting iridium powder and palladium sponge. After solidification, the iridium-palladium alloy was edge forged at 1500 0, hot rolled and cold rolled to sheet. A palladium-rich gold tie line terminal alloy containing 15% gold and balance essentially palladium was prepared by melting palladium sponge and gold grain in an induction furnace under argon. The solidified palladium-gold alloy was forged at 1000 C. and cold rolled to sheet. The iridium-palladium alloy, which was to be clad with the palladium-gold alloy was wrapped in an envelope with the cladding alloy and the edges were sealed-off by argon arc welding while evacuating the air from within the cladding. The enveloped alloy was rolled at 1200 C. and then at room temperature to produce the coated body comprising the iridium-palladium core and the palladiumgold cladding. Oxidation resistance of the thus produced coated body was tested by heating at 1200 C. for 100 hours in air. Loss in weight of the coated body during the test was very satisfactorily low and was only about 16.5% of the weight loss experienced by an uncoated strip of the iridium alloy containing 1% palladium when subjected to the same test.

In view of the teachings herein, many different useful combinations of conjugate tie line compositions for coated bodies of the invention can be obtained by selection from the ternary alloy systems referred to herein. In selecting the conjugate compositions, a tie line should be chosen in a system where the equilibrium temperature is near the temperature of intended use, e.g. within 100 C., or advantageously within 50 C., of the temperature of intended use. Conjugate compositions for the invention are obtainable from the illustrative diagrams of the drawing and also by metallurgically determining tie line terminal compositions in palladium-gold and platinum-gold ternary systems with ruthenium, iridium, tungsten or molybdenum at equilibrium temperatures of intended use, which in the present invention include temperatures from 700 C. and upwards to 1450 C. and higher. It is not in fact absolutely necessary to determine the composition of more than one phase in the tw-phase alloy in order to draw any tie line, since a straight line will invariably pass through the points representing the alloy itself and both phases. If one phase is ascertained, the second phase will therefore be of the composition at the point where the tie line intersects the boundary line.

Naturally, substantial valuable protection can be obtained by the use of metallic pairs that are not exactly on the ends of the tie lines. In general, a tolerance is permissible. Broadly, any metallic body of composition such that it lies within a circle or part of a circle struck at a radius of by Weight from the point denoting a metal or alloy of terminal composition can be used with any metallic coating of composition such that it lies within a similar circle or part of a circle round the point denoting the corresponding terminal alloy at the other end of the tie line, provided the alloys have solidus temperatures above that of the elevated temperature of the intended use. Such part-circles are shown by lines B and C around points B and C in FIG. 1. Also, and with regard to other figures of the drawing, circles of 5 weight percent around terminal compositions sometimes include both two-phase and single-phase alloys, it being understood that the single-phase compositions are advantageous for the invention.

The coatings of the protecting alloys can be thin, for example 0.001" or more.

In FIG. 1, the tie line Z shows that a body, e.g. a core, base, etc., made of an alloy containing 99% ruthenium and 1% palladium can be protected by a coating, e.g. sheath, cladding, plating, etc., made of an alloy of 73% palladium, 25% gold and 2% ruthenium. Similarly, tie lines in other figures of the drawing illustrate conjugate tie line compositions, which are substantially at tie line terminals, for combinations of body metals and coating metals of illustrative examples of the invention, as set forth in the following table.

TABLE Fig. Body Composition Coating Composition 1 Substantially 100% Ru 62% Pd, 37% Au, 1% Ru 1 99% R11, 1 U Pd 73% Pd, 25% A11,2% Ru 2a. Substantially 100% Ir Pd, 16% Au, 5% I1 2a 88 0 Ir, 12% Pd. 79% Pd, 6% Au, 15% Ir 2b 93% Ir, 7% Pd 63.5% Pd, 36% Au, 0.5% Ir 2b-- 91% Ir, 9% P 71% Pd, 27% Au, 2% 3a Substantially 100% Mo. 44% Pd, 54% Au, 2% Mo 99% Mo, 1% P 55% Pd, 42.5% Au,2 5%Mo 98% Mo, 2% Pd 66% Pd, 30.5% An, 3.5% M0 99% W, 1% P subsitantially 100% W o 7 .II. 7 Pt, 1% Au, 30% w 7 74% Pt, 1% Au, 15% W 13% Pt, 87% Au For producing coated bodies in accordance with the invention, the alloy used for the body can be prepared by conventional melting or powder metallurgical techniques. The alloy for the coating usually should be prepared by vacuum melting or by powder metallurgy since it has been found that in air-melting gas is entrapped within the alloy. Having gas trapped in the body metal can detrimentally result in buildingup excessive gas pressures within the coated body when heated to elevated temperatures. Where the coating is to be applied as cladding or the like, the alloys can be worked to tube or sheet. The coating can be applied by a variety of techniques depending on the form of the article to be coated, For instance, the application of the coating to the body can be accomplished by one or more of the following methods according to the particular needs for given articles. When the body is a sheet, the coating can be applied in sheet form by rolling. Thus, techniques where the body is encased in the manner of a picture frame and the interior of the coating is evacuated and sealed can be employed satisfactorily. Coated 'wire in accordance with the invention can be prepared by techniques wherein the body is a core and the coating alloy is in the form of a tube or sheath which is placed over the core. The ends of the core and sheath are evacuated and sealed and the compound body is then swaged and hot drawn to coated wire.

When the body is of complex shape the coating can be applied by electrodeposition methods in which the required metals for the coating are applied independently and then fused to produce the required conjugate alloy composition. In some instances, direct electrodeposition of the coating can be performed. Also, the coating can be applied by hot dipping the body into the molten coating alloy or by metal spraying or plasma-arc spraying. Furthermore, the process described in United Kingdom patent specification No. 952,493, whereby a dispersion of a flake powder of a platinum group metal is applied, volatilized or decomposed, and sintered is also suitable for applying metal coatings in accordance with the invention. In the light of the teachings herein, additional methods for combining the coating in the body to produce useful articles will be apparent to those skilled in the art.

It is to be made clear to those skilled in the art that the special diffusion resistant combinations of metals for the bodies of the invention do not form diffusion bonds with each other at the temperature of intended use but a bond can readily be effected at a different temperature.

The present invention is particularly applicable in the production of coated metallic bodies for use where oxidation resistance at elevated temperatures of 700 C. and higher, e.g. 1450 C., is required. As indicated hereinbefore, the invention is especially applicable to production of high strength oxidation resistant coated bodies wherein the metallic body is readily oxidizable and has high strength at elevated temperature, that is bodies of ruthenium-rich, iridium-rich, tungsten-rich and molybd num-rich metals with or without palladium. It will be understood that for obtaining very high strength the body can be of very high amounts, e.g. 90% or more, of the high strength readily oxidizable elements referred to herein. Coated bodies of the invention include oxidation resistant coated sheet, strip, plate, tubing, wire, rod, bar and like products which also have corrosion-resistant advantages especially Where one member of the metallic body is ruthenium-rich or iridium-rich. Further, the invention contemplates coated bodies of iridium for use as spinners in the production of glass fiber where the use can be at 1200 C. Also, the invention contemplates turbine blades made of molybdenum or tungsten metals with oxidation resistant coatings in accordance with the invention for use at temperatures of 1200 C. and higher. Moreover, although it has been generally implied herein that the coating metal is usually an exterior surface component which protects the body against exposure to a detrimental environment, it will also be understood that where the need arises, e.g. where corrosion resistant advantages of iridium and/or ruthenium are needed, the body metal can be a protection for the coating metal.

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.

I claim:

1. A coated metallic article for use at temperatures of 700 C. and higher comprising a body component and a coating component with the compositions of said two components being different compositions characterized by solidus temperatures higher than the temperature of intended use, 'with at least one of said components being an alloy containing gold and a metal from the group palladium and platinum and with the two components being substantially of the compositions at the opposite terminals of an alloy tie line having the terminals thereof at single-phase terminal solid solution compositions on the boundary line between single-phase alloys and twophase alloys on a ternary metallurgical equilibrium diagram for said temperature of use having gold at one apex, a metal from the group palladium and platinum at a second apex and a metal from the group ruthenium, iridium, tungsten and molybdenum at a third apex, said alloy tie line passing through a point representing on said equilibrium diagram the composition of an alloy characterized at said temperature by a two-phase microstructure wherein one of the phases is of the terminal solid solution composition at one terminal of the tie line and the other phase is of the terminal solid solution composi tion at the other terminal of said tie line.

2. A coated article in accordance with claim 1 wherein the body contains at least 50% of one metal from the group consisting of ruthenium, iridium, tungsten and molybdenum.

3. A coated article in accordance with claim 1 wherein the body contains at least 50% of one metal from the group consisting of ruthenium, iridium, tungsten and molybdenum and wherein the coating is a palladium-gold alloy containing up to about 40% gold characterized by a solidus temperature greater than 1200 C.

4. A coated article in accordance with claim 1 for use at temperatures of 1200 C. and higher wherein the body contains at least of one metal from the group consisting of ruthenium, iridium, tungsten and molybdenum and the coating is a palladium-gold alloy containing up to about 40% gold characterized by a solidus temperature of at least about 1200 C.

5. A coated metal article for use at temperatures of 700 C. and higher comprising a metallic body and a metallic coating wherein the body and the coating are different metal compositions, wherein at least one of said different compositions is an alloy containing gold and one metal from the group consisting of palladium and platinum and wherein the compositions of said body and said coating are mutually correlated in accordance with a tie line terminal relationship such that, in relation to the terminals of an alloy tie line on a ternary metallurgical equilibrium diagram for one of the ternary isothermal equilibrium systems ruthenium-palladium-gold, iridium-palladium-gold, tungsten-palladium-gold, molybdenum-palladium-gold, ruthenium-platinum-gold, iridium-platinum-gold, tungsten-platinum-gold and moly-bdenum-platinum-gold in equilibrium at the temperature of intended use, said alloy tie line having opposite terminals at single-phase terminal solid solution compositions on the boundary line between single-phase alloys and twophase alloys on said diagram and said tie line passing through a point representing on said equilibrium diagram the composition of an alloy characterized at said temperature by a two-phase microstructure wherein one of the phases is of the terminal solid solution composition at one terminal of the tie line and the other phase is of the terminal solid solution composition at the other terminal of said tie line, the body composition is Within 5 Weight percent of the composition at one terminal of said tie line and the coating composition is within 5 weight percent of the composition at the other terminal of said tie line, said coated article being characterized by resistance to interdiffusion of said body and said coating when at said temperature of intended use.

6. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the ruthenium-palladiumgold metallurgical system.

7. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the iridium-palladium-gold metallurgical system.

8. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the tungsten-pal ladium-gold metallurgical system.

9. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the molybdenum-palladium-gold metallurgical system.

10. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the rutheniumplatinum-gold metallurgical systems.

11. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the iridiumplatinum-gold metallurgical system.

12. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the tungstenplatinum-gold metallurgical system.

13. A coated metal article as set forth in claim 5 wherein the compositions of the body component and the coating component are compositions in the molybdenum-platinum-gold metallurgical system.

14. A coated article in accordance with claim 5 for use at elevated temperatures of 1200 C. and high r wherein the body composition contains at least 50% of metal from the group consisting of ruthenium, iridium, tungsten and molybdenum.

15. A coated article in accordance with claim 5 for use at elevated temperatures of 1200 C. and higher wherein the body composition contains at least 50% of one metal from the group consisting of ruthenium, iridium, tungsten and molybdenum and wherein the coating composition is a palladium-gold alloy containing up to about 40% gold.

16. A coated article in accordance with claim 5 for use at temperatures of 1200 C. and higher wherein the body contains at least 90% of one metal from the group consisting of ruthenium, iridium, tungsten and molybdenum and wherein the coating composition is a palladium-gold alloy containing up to about 40% gold.

17 A coated article in accordance with claim 5 wherein the body composition is one metal selected from the group consisting of tungsten, tungsten-palladium alloys containing up to about 5% palladium, molybdenum, and molybdenum-palladium alloys containing up to about 5% palladium and wherein the coating composition is a palladium-gold alloy containing up to about 40% gold characterized by a solidus temperature greater than 1200 C.

References Cited UNITED STATES PATENTS HYLAND BIZOT, Primary Examiner US. Cl. X.R.

g gg UNITED sums PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. Dated March 97 Inventor 9 DAVID WADE RHYS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

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