Oxidation-resistant layer for TiAl materials and method for the production thereof

Abstract

The present invention relates to a protective layer for TiAl materials for affording protection against oxidation, said protective layer having a layer sequence which, proceeding from the inner side facing toward the TiAl material (1), has an inner aluminum oxide layer (5), a first gradient layer (6) comprising aluminum and a base metal with a base metal content increasing outward toward the surface side, a base metal layer (7), a second gradient layer (8) comprising aluminum and a base metal with an aluminum content increasing outward toward the surface side, and an outer aluminum oxide layer (9), and also to a method for the production thereof.

Claims

1. A protective layer for protecting a TiAl material against oxidation, wherein the protective layer has a layer sequence which, proceeding from an inner side facing toward the TiAl material, comprises an inner aluminum oxide layer, a first gradient layer comprising aluminum and a base metal with a base metal content increasing outward toward a surface side, a base metal layer, a second gradient layer comprising aluminum and a base metal with an aluminum content increasing outward toward the surface side, and an outer aluminum oxide layer.

2. The protective layer of claim 1, wherein a transition from the inner aluminum oxide layer to the first gradient layer is continuous, with an aluminum oxide content which decreases outward from the inner side and an aluminum content which increases outward from the inner side, and/or wherein a transition from the second gradient layer to the outer aluminum oxide layer is continuous, with an aluminum oxide content which increases outward from the inner side and an aluminum content which decreases outward from the inner side.

3. The protective layer of claim 1, wherein the base metal of the first and second gradient layers and the base metal of the base metal layer are selected from metals which are oxidation-resistant at temperatures of up to 900 C.

4. The protective layer of claim 1, wherein the base metal of the first and second gradient layers and the base metal of the base metal layer comprise one or more elements selected from iron, cobalt, nickel, chromium, gold, platinum, iridium, palladium, osmium, silver, rhodium, ruthenium.

5. The protective layer of claim 1, wherein the protective layer further comprises a thermal barrier layer and/or an abrasion-resistant layer at the surface.

6. The protective layer of claim 5, wherein the thermal barrier layer or the abrasion-resistant layer comprise zirconium oxide or zirconium oxide partially stabilized with yttrium oxide.

7. The protective layer of claim 5, wherein the abrasion-resistant layer has a thickness of from 5 m to 50 m.

8. The protective layer of claim 5, wherein the thermal barrier layer has a thickness of greater than or equal to about 150 m.

9. The protective layer of claim 1, wherein the protective layer further comprises a diffusion barrier layer with respect to the base metal or other constituents of the layer arranged between the TiAl material and the inner aluminum oxide layer.

10. The protective layer of claim 9, wherein the diffusion barrier layer is formed from coarse-grained aluminum oxide, a grain size of the aluminum oxide being ranging from 10 nm to 1 m.

11. The protective layer of claim 1, wherein the protective layer further comprises an adhesion promoter layer arranged between the TiAl material and the inner aluminum oxide layer.

12. The protective layer of claim 11, wherein the adhesion promoter layer is formed from initially amorphous aluminum oxide which crystallizes during a subsequent heat treatment and/or at elevated temperatures of more than 400 C. during use.

13. The protective layer of claim 11, wherein the adhesion promoter layer is arranged on the inside, facing toward the TiAl material, and a diffusion barrier layer is arranged between the adhesion promoter layer and the inner aluminum oxide layer.

14. The protective layer of claim 13, wherein the adhesion promoter layer and the diffusion barrier layer are formed as a graduated layer with a proportion of crystalline aluminum oxide which increases from the inside outward.

15. A TiAl material, wherein the material comprises the protective layer of claim 1.

16. The material of claim 15, wherein the material is a component of a stationary gas turbine or an aero engine.

17. The material of claim 15, wherein the material is a component of a turbomachine.

18. A method for producing a protective layer on a TiAl material, wherein the method comprises applying by physical vapor deposition (PVD) or chemical vapor deposition (CVD) and proceeding from an inner side facing toward the TiAl material, an inner aluminum oxide layer, a first gradient layer comprising aluminum and a base metal with a base metal content increasing outward toward the surface side, a base metal layer, a second gradient layer comprising aluminum and a base metal with an aluminum content increasing outward toward the surface side, and an outer aluminum oxide layer.

19. The method of claim 18, wherein additionally an outer thermal barrier layer or an abrasion-resistant layer is deposited by electron beam evaporation or by being sprayed on and/or an inner diffusion barrier layer and/or adhesion promoter layer are deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD).

20. The method of claim 18, wherein a pre-oxidation layer is applied to the TiAl material by targeted oxidation at a temperature of less than 600 C. and for a period of time of less than 15 minutes, or is formed by an electrolytic process in a thickness of less than 500 nm.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the appended drawing

(2) The FIGURE shows, in a purely schematic fashion, an illustration of the structure of a layer according to the invention in cross section.

DETAILED DESCRIPTION OF EMBODIMENTS

(3) 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.

Exemplary Embodiment

(4) The FIGURE shows an exemplary embodiment of the present invention, the invention not being limited to this exemplary embodiment.

(5) The FIGURE shows a cross section through an exemplary embodiment of a protective layer according to the present invention, wherein, proceeding from the TiAl material 1, a pre-oxidation layer 2, an adhesion promoter layer 3, a diffusion barrier layer 4, an inner aluminum oxide layer 5, a first, inner gradient layer 6, a base metal layer 7, a second, outer gradient layer 8, an outer aluminum oxide layer 9 and a thermal barrier layer 10 are shown.

(6) The TiAl material 1 may be any desired metal alloy whose main constituents are titanium and aluminum, i.e. whose quantitatively greatest proportions in percent by weight are titanium and aluminum, for example intermetallic titanium aluminide alloys.

(7) The pre-oxidation layer 2, which has a thickness of approximately up to 200 nm in the present exemplary embodiment, may be formed on the TiAl material 1 by, for example, an electrolytic process at low temperatures in the range of from about 10 C. to at most about 500 C.

(8) According to the exemplary embodiment, an adhesion promoter layer formed from amorphous aluminum oxide (Al.sub.2O.sub.3) is applied to the pre-oxidation layer 2 by physical vapor deposition or chemical vapor deposition.

(9) After the adhesion promoter layer 3, provision is made of a diffusion barrier layer 4, the latter serving as a diffusion barrier for the constituents provided in the subsequent layer structure, in particular a base metal. The diffusion barrier layer 4 is formed from crystalline aluminum oxide (Al.sub.2O.sub.3), which has a coarse-grained form with grain sizes in the range of from about 10 nm to about 1 m.

(10) In the exemplary embodiment shown, the adhesion promoter layer 3 and the diffusion barrier layer 4 are formed as a graduated layer having, together, a layer thickness of approximately 2 m, with a gradient being formed over the layer thickness, along which the proportion of the amorphous aluminum oxide decreases outward in favor of the crystalline aluminum oxide.

(11) In the same way, the inner aluminum oxide layer 5 is applied in such a way that there is a continuous transition to the inner, first gradient layer 6 in terms of the aluminum oxide/aluminum ratio. Correspondingly, the aluminum oxide proportion decreases in favor of an increasing aluminum proportion at the transition from the inner aluminum oxide layer 5 to the first gradient layer 6 formed from aluminum and platinum, until predominantly aluminum is present in the inner region of the gradient layer 6, the aluminum proportion of the first gradient layer 6 decreasing outward again within the first gradient layer in favor of an increasing platinum proportion. In the first, inner gradient layer 6, the layer is therefore depleted of aluminum, and enriched with platinum, from the inside outward, such that predominantly platinum is present at the base metal layer 7, which is formed as a pure platinum layer in the present exemplary embodiment, or the inner gradient layer 6 merges continuously into the base metal layer 7.

(12) In the subsequent second, outer gradient layer 8, the proportion of platinum is reduced again in favor of aluminum, such that, at its outer edge, the second gradient layer 8 comprising platinum and aluminum has a predominant proportion of aluminum, which in turn merges continuously with an increasing aluminum oxide proportion into the outer aluminum oxide layer 9, such that the aluminum is gradually reduced in favor of the aluminum oxide, until a pure aluminum oxide layer 9 is present.

(13) The layer thickness of the inner aluminum oxide layer 5 and of the first gradient layer together is approximately 3 m, while the platinum layer 7 has a thickness of approximately 1 m and the second, outer gradient layer 8 and the outer aluminum oxide layer 9 together have a thickness of approximately 7 m.

(14) The outwardly final thermal barrier layer 10 of the present embodiment is formed from zirconium oxide partially stabilized with yttrium oxide and has a thickness of 150 m. The thermal barrier layer 10 can be applied by, for example, electron beam evaporation or plasma spraying.

(15) In another embodiment, provision can be made not of a thermal barrier layer but of an abrasion-resistant layer 10, which can likewise be formed from zirconium oxide partially stabilized with yttrium oxide; however, the layer thickness is smaller and can vary, for example, in the region of approximately 10 m.

(16) The described layer structure provides an oxidation-resistant layer for TiAl materials which, even at high temperatures of above 750 C., not only prevents progressive oxidation, but also avoids a situation in which the TiAl base material experiences phase transformations and therefore embrittlement of the base material during application of the protective layer or as a result of thermal loading during operation. It can thereby be ensured that the base material neither undergoes excessive oxidation nor becomes embrittled in the marginal region, which could have a negative influence on the mechanical properties of the component.

(17) Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

LIST OF REFERENCE NUMBERS

(18) 1 TiAl base material

(19) 2 Pre-oxidation layer

(20) 3 Adhesion promoter layer

(21) 4 Diffusion barrier layer

(22) 5 Inner aluminum oxide layer

(23) 6 First, inner gradient layer

(24) 7 Base metal layer

(25) 8 Second, outer gradient layer

(26) 9 Outer aluminum oxide layer

(27) 10 Thermal barrier layer

(28) 10 Abrasion-resistant layer