METHOD OF MANUFACTURING AN OXIDATION-RESISTANT COMPONENT OF A MOLYBDENUM BASE ALLOY

Abstract

The present invention relates to a method of producing a component of an Mo base alloy which is protected against high-temperature oxidation, and a correspondingly produced component.

The method comprises: provision of a semifinished part composed of a Mo base alloy, provision of an Si-containing slip or of a Si-containing powder, application of the slip to the semifinished part and diffusion annealing of the semifinished part together with the applied slip to form a Si-containing outer layer or transfer of at least part of the silicon present in the powder via the gas phase to the semifinished part by means of a diffusion heat treatment of the semifinished part together with the Si-containing powder which is arranged at a distance from the semifinished part.

Claims

1.-13. (canceled)

14. A method of producing a component of a Mo base alloy which is protected against high-temperature oxidation, wherein the method comprises: provision of a semifinished part composed of a Mo base alloy, provision of a Si-containing slip which comprises powder of at least one of Mo, W, B, Ta, Cr, Fe, Ti and alloys thereof or of a Si-containing powder which comprises a mixture of Si and Al.sub.2O.sub.3 powders, (a) application of the slip to the semifinished part and diffusion annealing of the semifinished part together with the applied slip to form a Si-containing outer layer or (b) transfer of at least part of the silicon present in the powder via a gas phase to the semifinished part by a diffusion heat treatment of the semifinished part together with the Si-containing powder which is arranged at a distance from the semifinished part but in a vicinity of the semifinished part.

15. The method of claim 14, wherein a molybdenum silicide or molybdenum disilicide layer is formed on at least part of the surface of the component as a result of the diffusion annealing or the diffusion heat treatment.

16. The method of claim 14, wherein after the diffusion annealing or the diffusion heat treatment conditioning of the component by a high-temperature oxidation at a temperature above 900 C. is carried out.

17. The method of claim 16, wherein the conditioning is carried out at a temperature of from 1000 C. to 1400 C. for from 2 hours to 100 hours.

18. The method of claim 14, alternative (b), wherein the powder for transferring the silicon via the gas phase comprises one or more halogens.

19. The method of claim 18, wherein the powder comprises one or more of NH.sub.4F, NH.sub.4Cl, and NaF.

20. The method of claim 14, alternative (b), wherein the powder for transferring the silicon via the gas phase is arranged in a vessel underneath the semifinished part.

21. The method of claim 14, alternative (b), wherein the diffusion heat treatment is carried out at a temperature above 900 C.

22. The method of claim 21, wherein the diffusion heat treatment is carried out at a temperature of from 1000 C. to 1300 C., with a hold time at the temperature of from 0.5 to 5 hours.

23. The method of claim 21, wherein the diffusion heat treatment is carried out under a protective gas atmosphere.

24. The method of claim 14, alternative (a), wherein the slip comprises Si powder or Si-containing powder, a solvent and a binder.

25. The method of claim 24, wherein the binder comprises a polyvinyl alcohol and/or a resin.

26. The method of claim 14, alternative (a), wherein the slip comprises powder of at least one of aluminum oxide, zirconium oxide, yttrium oxide, hafnium oxide, neodymium oxide, silicon carbide, silicon nitride.

27. The method of claim 14, alternative (a), wherein the slip comprises powder particles having an average or maximum particle size of from 0.5 to 100 m.

28. The method of claim 14, alternative (a), wherein the slip is applied by dipping the semifinished part into the slip, spraying the slip onto the semifinished part or printing the slip onto the semifinished part.

29. The method of claim 14, alternative (a), wherein the slip is applied by onto the semifinished part by screen printing or template printing.

30. The method of claim 14, alternative (a), wherein the diffusion annealing is carried out at a temperature above 900 C.

31. The method of claim 30, wherein the diffusion annealing is carried out at a temperature of from 1000 C. and 1400 C., with a hold time at the temperature of from 1 minute to 3 hours.

32. A component of a Mo base alloy which is protected against high-temperature oxidation, wherein the component is produced by the method of claim 14.

33. The component of claim 32, wherein the component is a component of a turbomachine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings schematically show in

[0028] FIG. 1 a depiction of an arrangement for producing an Si-containing outer layer via the gas phase,

[0029] FIG. 2 in subfigures a) and b), a depiction of the application of a slip to a semifinished part,

[0030] FIG. 3 a depiction of a cross section through the outer region of a semifinished part which has been treated as shown in FIG. 1 or FIG. 2, and in

[0031] FIG. 4 a depiction of a cross section through the outer region of the semifinished part of FIG. 2 after conditioning.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0032] 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.

[0033] In various working examples, technical-grade molybdenum, a molybdenum alloy comprising 9 at. % of silicon and 8 at. % of boron with molybdenum as balance and also a molybdenum alloy comprising 27 at. % of titanium, 13.5 at. % of silicon, 5.5 at. % of boron and 1 at. % of iron with molybdenum as balance have been used as materials of the treated semifinished parts. In the case of Mo base alloys, oxides such as La.sub.2O.sub.3 can additionally be added to the material. An overview of alloys from which the semifinished part can be made is given in the following table:

TABLE-US-00001 Proportion in at. % alloy No. Mo Si Ti B Fe Nb Hf Al Cr W V 1 Balance 9 8 2 Balance 13.5 27 5.5 1 3 Balance 9 8 2.7

[0034] FIG. 1 shows an example of an arrangement for producing an Si-containing outer layer in a semifinished part 4 via the gas phase. For this purpose, a vessel 1, for example made of aluminum oxide, which has a lid 2 and in which a silicon powder containing NH.sub.4F is present is provided. The semifinished part 4 to be treated is located above the silicon powder so that when the vessel 1 is heated to a temperature of about 1190 C. in an argon atmosphere for a time of 2 hours, silicon can diffuse into the outer layer of the semifinished part 4.

[0035] The diffusion heat treatment results in formation of an outer region of the semifinished part 4 as is shown in cross section in FIG. 3. A silicide layer 6 has been formed on top of the base material 5 by inward diffusion of silicon.

[0036] After the formation of the silicide layer 6 by means of the heat treatment under an argon atmosphere, as has been shown schematically in FIG. 1, the semifinished part 4 is aged in air at a temperature of about 1400 C. for 8 hours so that a silicate layer 8 is formed on top of the silicide layer 6 by oxidation of the silicon, while an interdiffusion layer 7 which serves as silicon reservoir is formed between the silicide layer 6 and the base material. This structure of the outer region is shown in FIG. 4.

[0037] FIG. 2 shows, in the subfigures a) and b), an alternative working example in which the silicide layer 6 is formed by a slip 12, which is present in a vessel 10, being applied by means of a brush 11 to the semifinished part 4 and drying at about 50 C. subsequently being carried out. A heat treatment under reduced pressure at 1400 C. for 1 hour is subsequently carried out so that silicon can once again penetrate into the base material 5 of the semifinished part 4 and a silicide layer 6, as depicted in FIG. 3, is formed. The semifinished part 4 which has been enriched with silicon is appropriately conditioned so that formation of the outer region as depicted in FIG. 4 and as has been described above occurs.

[0038] The enrichment with silicon by means of the slip process can of course be applied to all molybdenum-containing materials in the same way as the silicon gas-phase coating procedure.

[0039] In one working example, the slip is formed by a silicon powder having a particle size of 45 m in an aqueous solution, with additional components, for example boron powder having a particle size of 35 m or the like, being able to be added to the slip solution.

[0040] Although the present invention has been described in detail with the aid of the working examples, it will be self-evident to a person skilled in the art that the invention is not restricted to these working examples but instead that modifications made by omitting individual features or different combinations of features may be made without going outside the scope of protection of the accompanying claims. In particular, the present disclosure includes all combinations of the individual features indicated in the various working examples, so that individual features which have been described only in connection with one working example can also be used in other working examples or combinations of individual features which are not explicitly presented.