COMPONENT OF A MOLYBDENUM ALLOY AND METHOD FOR FORMING AN OXIDATION PROTECTION LAYER THEREFOR

Abstract

Disclosed is a method for improving the high-temperature stability of a component, in particular a blade of a turbomachine, formed at least partially from a molybdenum alloy that, besides molybdenum, silicon, boron and titanium, comprises iron and/or yttrium. The method comprises depositing a diffusion barrier layer formed from technically pure molybdenum or tungsten or being an alloy based on molybdenum and/or tungsten at least on an outer surface, which comprises the molybdenum alloy, of the component, and depositing silicon on the diffusion barrier layer to form molybdenum silicides and/or tungsten silicides.

Claims

1. A method for improving the high-temperature stability of a component which is formed at least partially from a molybdenum alloy that, besides molybdenum, silicon, boron and titanium, comprises iron and/or yttrium, wherein the method comprises depositing at least on an outer surface, which comprises the molybdenum alloy, of the component a diffusion barrier layer formed from technically pure molybdenum or tungsten or being an alloy based on molybdenum and/or tungsten, and depositing silicon on the diffusion barrier layer after deposition of the diffusion barrier layer to form molybdenum silicides and/or tungsten silicides.

2. The method of claim 1, wherein the component is a blade of a turbomachine.

3. The method of claim 1, wherein the alloy based on molybdenum and/or tungsten comprises niobium and/or tantalum.

4. The method of claim 1, wherein boron is deposited with the silicon in order to form molybdenum boride and/or tungsten boride and/or molybdenum borosilicides and/or tungsten borosilicides.

5. The method of claim 3, wherein boron is deposited with the silicon to form molybdenum boride and/or tungsten boride and/or molybdenum borosilicides and/or tungsten borosilicides.

6. The method of claim 1, wherein the deposition of the diffusion barrier layer is carried out by physical vapor deposition.

7. The method of claim 7, wherein the deposition of the diffusion barrier layer is carried out by sputtering.

8. The method of claim 1, wherein the deposition of the silicon is carried out by chemical vapor deposition.

9. The method of claim 1, wherein the method further comprises carrying out a heat treatment to form the molybdenum silicides and/or tungsten silicides after deposition of the silicon.

10. The method of claim 1, wherein the method further comprises carrying out a heat treatment in an atmosphere containing oxygen after formation of the molybdenum silicides and/or tungsten silicides, to form an oxide layer.

11. The method of claim 9, wherein the method further comprises carrying out a heat treatment in an atmosphere containing oxygen after formation of the molybdenum silicides and/or tungsten silicides, to form an oxide layer.

12. The method of claim 1, wherein the diffusion barrier layer comprises at least 90 wt % of molybdenum.

13. The method of claim 1, wherein the diffusion barrier layer comprises no tungsten.

14. The method of claim 1, wherein the diffusion barrier layer comprises no molybdenum.

15. The method of claim 1, wherein the diffusion barrier layer comprises both molybdenum and tungsten.

16. The method of claim 1, wherein the diffusion barrier layer is formed from technically pure molybdenum or tungsten

17. A component for high-temperature applications, wherein the component is formed at least partially from a molybdenum alloy that, besides molybdenum, silicon, boron and titanium, comprises iron and/or yttrium, wherein a diffusion barrier layer formed from technically pure molybdenum or tungsten or being an alloy based on molybdenum and/or tungsten is arranged at least on a region, which comprises the molybdenum alloy, of the component, and wherein a layer which comprises molybdenum silicides and/or tungsten silicides is arranged on the diffusion barrier layer.

18. The component of claim 17, wherein an oxide layer is arranged on the layer comprising molybdenum silicides and/or tungsten silicides.

19. The component of claim 17, wherein the component is a component of a turbomachine.

20. The component of claim 17, wherein the component is a guide vane or rotor blade of a turbomachine.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0028] The appended drawing (FIGURE) purely schematically an in a non-limiting manner shows the method sequence during the coating of a substrate made of an Mo—Si—B—Ti—Fe alloy.

DETAILED DESCRIPTION OF EMBODIMENT OF THE INVENTION

[0029] 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 drawing making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

[0030] The appended FIGURE shows in the subfigures a) to e) the method steps during the application of an oxidation protection layer according to the invention onto a substrate of a highly alloyed Mo—Si—B—Ti—Fe alloy comprising molybdenum, silicon, boron, Ti and iron as alloy constituents, the proportion of the alloy elements decreasing in the order of the list. As a molybdenum alloy, the main constituent molybdenum is present in the greatest proportion.

[0031] In substep a), a substrate 1 which is formed from an Mo—Si—B—Ti—Fe alloy is provided. A diffusion barrier layer 2 is deposited by means of sputtering on a surface of the substrate 1, the diffusion barrier layer 2 being formed from a molybdenum alloy which has small amounts of tantalum and/or niobium alloyed with it so as to match the thermal expansion coefficient to that of the substrate. In particular, the molybdenum alloy for the diffusion barrier layer may be an alloy in which the proportion of molybdenum is ≧90 wt %. The molybdenum may also be fully or partially replaced with tungsten.

[0032] After the deposition of the diffusion barrier layer 2 in substep b), silicon with a small proportion of boron is deposited by means of chemical vapor deposition in substep c) so that a silicon layer 3 with boron doping is formed on the diffusion barrier layer 2. At the same time, diffusion of silicon into the diffusion barrier layer 2 or diffusion of molybdenum out into the applied silicon layer 3 may occur by the effect of temperature during the chemical vapor deposition, so that a silicide layer 4 is formed. This is reinforced in process step d) by carrying out a heat treatment of the substrate with the layers 2, 3 applied thereon, so that all of the applied silicon with the corresponding proportion of boron is contained in the silicide layer 4, which comprises molybdenum silicides, molybdenum borides and molybdenum borosilicides, for example MoSi.sub.2, MoB, Mo.sub.5SiB.sub.2. By the effective temperature during the heat treatment, a diffusion zone 5 is furthermore formed between the substrate 1 and the diffusion barrier layer 2, but without diffusion of elements from the substrate 1 into the outer region of the coating having taken place.

[0033] The correspondingly produced component may already be used after process step d), since in a high-temperature application in an atmosphere containing oxygen the silicide layer 4 provides silicon for the formation of a silicon oxide layer 6. By the formation of an oxide layer 6 from slowly growing silicon dioxide, an oxidation protection effect is provided for the correspondingly coated component. Because of the boron in the form of borides or borosilicides contained in the silicide layer 4, there may also be boron oxides or silicon borosilicate in the oxide layer 6.

[0034] Although the invention has been described clearly with the aid of the exemplary embodiment, it is clear to the person skilled in the art that the invention is not restricted to this exemplary embodiment but rather that variants are possible in that individual features may be omitted or other types of combinations of features may be implemented, so long as the protective scope of the appended claims is not departed from.

LIST OF REFERENCE NUMERALS

[0035] 1 substrate [0036] 2 diffusion barrier layer of Mo and/or W, or molybdenum-rich and/or tungsten-rich alloys [0037] 3 silicon layer [0038] 4 silicide layer [0039] 5 diffusion zone [0040] 6 oxide layer