METHOD OF PROVIDING A METALLIC SURFACE WITH A PROTECTIVE CHROMIUM DIFFUSION LAYER

Abstract

The invention relates to a method of providing a metallic surface with a protective diffusion layer, wherein a chromium-containing slip is applied to the surface and is then subjected to a heat treatment in order to produce the protective diffusion layer. In addition to the chromium powder, the slip contains silicon powder in order to shorten the hold time required in the heat treatment.

Claims

1.-15. (canceled)

16. A method of providing a metallic substrate with a protective diffusion layer, wherein the method comprises applying a slip comprising chromium powder and silicon powder in one or more layers to the substrate, drying the slip and then subjecting the substrate to a heat treatment to form the protective diffusion layer.

17. The method of claim 16, wherein the metallic substrate is a component of a turbomachine.

18. The method of claim 16, wherein the metallic substrate comprises an alloy based on nickel and/or cobalt.

19. The method of claim 16, wherein a weight ratio of chromium powder to silicon powder in the slip ranges from 5:1 to 100:1.

20. The method of claim 19, wherein the weight ratio ranges from 7:1 to 50:1.

21. The method of claim 19, wherein the weight ratio ranges from 8:1 to 30:1.

22. The method of claim 16, wherein the chromium powder has a maximum particle size and/or an average particle size of less than or equal to 20 m.

23. The method of claim 16, wherein the silicon powder has a maximum particle size and/or an average particle size of less than or equal to 20 m.

24. The method of claim 22, wherein the silicon powder has a maximum particle size and/or an average particle size of less than or equal to 20 m.

25. The method of claim 16, wherein the slip comprises water and/or at least one liquid organic compound.

26. The method of claim 25, wherein the slip comprises screen printing oil.

27. The method of claim 16, wherein the slip is applied in a thickness of from 40 m to 10 mm.

28. The method of claim 16, wherein the slip is applied in a thickness of from 60 m to 2 mm.

29. The method of claim 16, wherein the heat treatment for forming the diffusion layer is carried out at a temperature ranging from 800 C. to 1250 C. with a hold time of from 1 hour to 24 hours.

30. The method of claim 16, wherein the heat treatment for forming the protective diffusion layer is carried out in an atmosphere containing one or more chromium halides.

31. The method of claim 16, wherein forming the protective diffusion layer is followed by alitizing the layer.

32. The method of claim 31, wherein the alitizing of the layer is carried out as gas-phase alitizing.

33. A slip for carrying out the method of claim 16, wherein the slip comprises chromium powder and silicon powder in a weight ratio of from 5:1 to 100:1.

34. The slip of claim 33, wherein the slip comprises the chromium powder and/or the silicon powder in a maximum particle size and/or an average particle size of less than or equal to 20 m.

35. A coated metallic substrate obtained by the method of claim 16.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings show in

[0022] FIG. 1 a polished section of a metallic surface with protective diffusion layer produced by the method of the invention;

[0023] FIG. 2 a polished section of the metallic surface shown in FIG. 1 after subsequent alitizing.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0024] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description in combination with the drawings making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

[0025] Production of a Protective Chromium Diffusion Layer.

[0026] A component made of the alloy PW 1484, which contained about 5% by weight of chromium, about 2% by weight of molybdenum, about 6% of tungsten, about 3% by weight of rhenium, about 9% by weight of tantalum, about 5% by weight of aluminum, about 10% by weight of cobalt, unavoidable impurities and minor amounts of further alloy constituents plus nickel as balance, was coated with a slip containing chromium powder and silicon powder in a ratio of 9.5:1. The slip additionally contained a small amount of CrCl.sub.3.

[0027] The slip was applied by spraying to the component to be coated. After application, the slip was dried at 50 C. under reduced pressure and subsequently at 100 C. in air for half an hour. The thickness of the slip which had been dried in this way was 150 m. The component was then subjected in a furnace to a heat treatment at a temperature of 1080 C. in an argon atmosphere containing a small amount of CrCl.sub.2 for 4 hours.

[0028] FIG. 1 shows a polished section (after molybdic acid etching) of a coated surface produced in this way (enlargement 1000:1).

[0029] As can be seen from FIG. 1, the protective diffusion layer 2 produced on the component 1 had a thickness of about 20 m. Analysis of the surface of the component showed the concentrations indicated in the table below of the elements present therein (in % by weight) as a function of the distance from the outer surface of the protective diffusion layer 2.

TABLE-US-00001 Distance from the surface in m Al Si Cr Fe Co Ni Mo Ta W Re 1 4.9 4.5 61.5 1.6 5.5 18.0 1.6 0.0 2.5 0.0 3 11.9 1.9 63.6 0.8 2.6 12.6 1.3 0.0 3.9 1.4 5 3.3 3.2 57.0 1.2 4.5 19.1 1.9 2.9 5.2 1.8 7 3.9 3.2 53.5 1.5 5.8 21.0 1.9 0.0 5.6 3.6 9 2.3 3.3 53.6 1.7 6.2 22.1 2.0 0.0 5.7 3.0 11 0.3 3.7 49.2 1.5 5.5 23.0 2.8 4.6 6.7 2.7 13 1.0 4.3 36.6 1.1 4.8 32.7 2.4 9.6 6.0 1.6 15 2.6 2.0 27.7 1.7 6.6 52.0 0.0 2.8 2.9 1.7 17 2.5 1.7 26.5 1.6 6.8 51.1 1.0 3.0 4.3 1.6 19 3.8 1.7 18.8 0.9 6.9 54.1 1.0 7.5 3.8 1.4 21 5.5 1.4 10.3 0.5 7.2 56.6 1.1 10.2 4.9 2.3 23 6.3 0.0 7.3 0.0 8.8 57.8 1.9 9.6 6.1 2.3 25 6.5 0.7 6.1 0.0 9.5 58.5 2.0 9.1 5.6 2.1 27 6.3 0.0 5.7 0.0 9.6 58.0 2.3 9.2 7.1 2.0 29 5.9 0.0 5.6 0.0 9.7 58.0 2.4 9.5 6.7 2.4

[0030] As can be seen from the table above, both chromium and silicon had diffused into the component 1 to a distance of about 20 m from the surface.

[0031] Alitizing of the Protective Diffusion Layer

[0032] The coated component was subsequently subjected to gas-phase alitizing in which the aluminum-containing donor material was deposited by means of the activator AlF.sub.3 on the component. Alitizing was carried out at a temperature of about 1100 C. for 6 hours in an argon/hydrogen atmosphere.

[0033] FIG. 2 shows a polished section (after molybdic acid etching) of the alitized coated surface (enlargement 500:1). As can be seen from FIG. 2, an about 60 m thick alitizing layer 3 which consisted predominantly of aluminum was formed on the about 20 m thick protective chromium diffusion layer 2, which is shown in FIG. 1, by means of the alitizing.

[0034] Although the present invention has been described in detail with the aid of the working examples above, it will be obvious to a person skilled in the art that the invention is not restricted to these working examples but that instead modifications involving leaving out individual features or realizing other combinations of the features are possible, as long as these modifications do not go outside the scope of protection of the accompanying claims.

LIST OF REFERENCE NUMERALS

[0035] 1 Component [0036] 2 Protective diffusion layer [0037] 3 Alitizing layer