METHOD FOR COATING A COMPONENT OF AN AIRCRAFT ENGINE WITH A WEAR-RESISTANT LAYER, AND COMPONENT FOR AN AIRCRAFT ENGINE WITH AT LEAST ONE WEAR-RESISTANT LAYER

Abstract

A method for coating a component of an aircraft engine with a wear-resistant layer, wherein the component is first coated at least regionally with a nickel- or cobalt-based alloy and subsequently aluminized. Also disclosed is a method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine.

Claims

1. A method for coating a component of an aircraft engine with a wear-resistant layer, wherein the method comprises (i) first coating the component at least regionally with a nickel- or cobalt-based alloy and subsequently aluminizing the thus coated component, or (ii) mixing a first powder of a nickel- or cobalt-based alloy with a second powder of aluminum and/or aluminum alloy, followed by thermally spraying the first and second powders at least onto a region of the component, in order to produce the wear-resistant layer, or (iii) producing a composite powder composed of a first powder consisting of a nickel- or cobalt-based alloy and of a second powder consisting of aluminum and/or an aluminum alloy, followed by thermally spraying the composite powder at least onto a region of the component, in order to produce the wear-resistant layer.

2. The method of claim 1, wherein in (i) the nickel- or cobalt-based alloy is aluminized by gas-phase aluminizing and/or by slip aluminizing and/or by powder pack aluminizing.

3. The method of claim 1, wherein in (i) the nickel- or cobalt-based alloy is aluminized by gas-phase aluminizing.

4. The method of claim 1, wherein in (i) the nickel- or cobalt-based alloy is aluminized by slip aluminizing.

5. The method of claim 1, wherein in (i) the nickel- or cobalt-based alloy is aluminized by powder pack aluminizing.

6. The method of claim 1, wherein in (i) the wear-resistant layer after aluminizing is subjected to a heat treatment.

7. The method of claim 6, wherein the heat treatment comprises diffusion annealing and/or is carried out at a reduced pressure relative to standard pressure and/or under a protective gas atmosphere.

8. The method of claim 1, wherein in (i) the nickel- or cobalt-based alloy, after application to the component and before aluminizing, is at least regionally nickel-plated.

9. The method of claim 1, wherein the nickel- or cobalt-based alloy is selected from CoMoCrSi alloys, NiMoCrSi alloys, and CoCrWNi alloys.

10. The method of claim 1, wherein the nickel- or cobalt-based alloy comprises a CoMoCrSi alloy, namely T800 having the following composition: TABLE-US-00001 Mo: 27-30 wt %, Cr: 16.5-18.5 wt % Si: 3-3.8 wt % balance Co and unavoidable impurities.

11. The method of claim 1, wherein the nickel- or cobalt-based alloy comprises a NiMoCrSi alloy, namely T700 having following composition: TABLE-US-00002 Mo: 31-34 wt %, Cr: 14.5-16.5 wt %, Si: 3-3.8 wt %, balance Ni and unavoidable impurities;

12. The method of claim 1, wherein the nickel- or cobalt-based alloy comprises a CoCrWNi alloy with following composition: TABLE-US-00003 Cr: 24.5-26.5 wt %, W:  6.5-8.0 wt %, Ni:  9.5-11.5 wt %, C: 0-0.6 wt %, in particular 0.42-0.55 wt %, balance Co and unavoidable impurities.

13. The method of claim 1, wherein the method comprises (i).

14. The method of claim 1, wherein the method comprises (ii).

15. The method of claim 1, wherein the method comprises (iii).

16. A method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine, wherein the method comprises admixing a nickel- or cobalt-based alloy with aluminum and/or an aluminum alloy, and jointly melting and/or atomizing a resultant mixture.

17. A component for an aircraft engine, wherein the component is provided at least regionally with a wear-resistant layer, the wear-resistant layer comprising an aluminized nickel- or cobalt-based alloy.

18. The component of claim 17, wherein the component has been produced by a method which comprises first coating the component at least regionally with a nickel- or cobalt-based alloy and subsequently aluminizing the thus coated component.

19. An aircraft engine which comprises at least one component according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0022] In the drawing,

[0023] the only FIGURE is a diagram showing the concentration of aluminum C in wear-resistant layer as a function of the distance A from an interface at different times t.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0024] In the FIGURE, the concentration of aluminum C is shown on the y-axis as a function of, on the x-axis, a distance A from an interface, marked with “0”, of a wear-resistant layer composed of a nickel- or cobalt-based alloy of a component of an aircraft engine, at three different times t.sub.1, t.sub.2, and t.sub.3. To the left of the interface of the original wear-resistant layer, marked with 0, is the aluminizing layer S generated in each case, while the wear-resistant layer extends to the right of the layer surface marked with 0.

[0025] According to the present state of the art, Ni- or Co-based wear-resistant layers cannot be used stably above 900° C. owing to their composition. The reason for this is the failure of the layer by oxidation at high temperatures. The present invention is based on the finding that aluminum as protection from temperature and oxidation can be introduced by diffusion into typical Ni- or Co-based wear-resistant layers, allowing the resultant aluminized wear-resistant layers to be operated reliably even above 900° C. It is intended preferably that the wear-resistant layers may be produced by thermal spraying.

[0026] The possibility of producing a high-temperature wear-resistant layer, by diffusion of aluminum as protection from oxidation into existing wear-resistant layers, was demonstrated in the following experiments. A total of three different wear-resistant layers, based on Co (for example, CoMoCrSi) or based on Ni (for example NiMoCrSi) were produced by thermal spraying on a component of an aircraft engine, and subsequently aluminized. In certain experiments, the aluminum was introduced into the respective wear-resistant layer by gas-phase aluminizing, and in other experiments via a slip route. Some of the coated components were subsequently heat-treated under reduced pressure.

[0027] The wear-resistant layers were each evaluated metallographically. Moreover, after the gas-phase aluminizing and also after the subsequent reduced-pressure heat treatment, elemental analysis (EDX) was carried out on a polished section in order to understand how far the aluminum is diffused into the wear-resistant layers.

[0028] 1. Gas-Phase Aluminizing

[0029] After the gas-phase aluminizing (CVD), aluminum incorporated by diffusion was detected both in the Ni-based wear-resistant layer and in the two Co-based wear-resistant layers. The Al content is highest at the layer surface and decreases with increasing distance A from the surface of the wear-resistant layer. This behavior is typical of diffusion layers. For this reason, subsequent to the gas-phase aluminizing, an additional diffusion anneal was carried out under reduced pressure, in order to achieve a more uniform distribution of the Al content over the layer thickness A of the wear-resistant layers. The evaluation of the elemental analysis (EDX) after the diffusion anneal is represented in the FIGURE. The aluminum content C of the layer surface of the aluminizing S drops after the heat treatment (dashed line t.sub.2); conversely, the aluminum is detectable at a greater distance from the layer surface in comparison to the wear-resistant layer after the aluminizing (dotted line t.sub.1). After this heat treatment as well, which was carried out at the same temperature as the aluminizing, there is still no homogeneous distribution of the aluminum over the layer thickness A. The temperature may be, for example, between 750° C. and 900° C. or more. By prolonging the heat treatment and/or by the temperatures during operation of the component in an aircraft engine, the aluminum diffuses further and is uniformly distributed in the wear-resistant layer, producing a uniform distribution of the Al concentration C over the thickness of the wear-resistant layer. This is represented schematically with the distribution curve t.sub.3.

[0030] 2. Slip Aluminizing

[0031] After the application of the Al-containing slip, it is diffusion-annealed by a heat treatment in protective gas. The temperature with this kind of aluminizing is lower by comparison with the gas-phase aluminizing. After the diffusion anneal, all of the wear-resistant layers exhibit a marked laminarity, consisting of a deposited layer, a diffusion zone, and a zone in which the lamellar thermal spray layer is still clearly apparent. The deposited layers produced differ significantly between the Co- and Ni-based layers. While in the case of Ni-based layer a dense deposited layer is formed, the layer in the case of the two Co-based layers is interdisposed with pores.

[0032] During the introduction of aluminum into the wear-resistant layer, care should be taken to ensure that the actual function of protection from wear is maintained. This means that, after the aluminizing of the layer, the hardness must be similar and the required wear resistance must be ensured. Too high or too low an Al content ought therefore to be generally avoided.

[0033] It has been shown that aluminum can be introduced into thermally sprayed wear-resistant layers by diffusion. Not only aluminized wear-resistant layers composed of Ni-based alloys but also those composed of Co-based alloys have been produced. In general it is possible for not only the Ni- or Co-based alloys stated above but instead all such alloys to be aluminized in the manner described.

[0034] Depending on the method, nature, and duration of a subsequent heat treatment, a high concentration of the aluminum is produced on the surface of the wear-resistant layer, the concentration decreasing to a greater or lesser extent with the distance A from the surface layer, depending on layer composition. It has been possible to show that the distribution of the aluminum can be adapted by subsequent heat treatment and hence by further diffusion of the aluminum. It may also be assumed that in the operation of the wear-resistant layer, at high temperatures and after a certain time, a homogeneous or at least quasi-homogeneous distribution of the aluminum comes about over time (t.sub.3).

[0035] Through the selection of the appropriate aluminizing method and through optimization of parameters, it is possible for each component to generate an optimal wear-resistant layer which exhibits an even or uneven profile in the aluminum concentration C, starting from the layer surface. The profile in the aluminum concentration C may even out after a certain time as a result of further diffusion in the operation of the component.

[0036] In order to achieve a homogeneous distribution of the aluminum over the layer thickness of the wear-resistant layer from the start, provision may be made to admix the Co- or Ni-based powder with aluminum powder before the thermal spraying. In the case of uniform mixing of the powder, the distribution of the aluminum in the layer assembly is consequently homogeneous or at least largely homogeneous directly after the thermal spraying. In the event of any difficulties caused by separation in the case of this technique, alternative provision may be made for the Co- or Ni-based powder to be adhered with Al powder. The composite powder produced in this way would likewise lead to homogeneous or at least largely homogeneous Al distribution in the resultant wear-resistant layer.

[0037] A further technique is that of admixing aluminum to the initial Ni- or Co-alloy from which the powder for the wear-resistant layer is produced. In this case, following atomization, the spray powder already has the desired Al content. With this variant, moreover, there is no likelihood of unwanted separation of the aluminum or powder separation.

[0038] The parameter values indicated in the documents for the definition of operating and measuring conditions for the characterization of specific properties of the subject matter of the invention are also deemed to be encompassed in the scope of the invention within the bounds of deviations—arising, for example, from measurement errors, systemic errors, weighing errors, DIN tolerances, and the like.

LIST OF REFERENCE SYMBOLS

[0039] C concentration of aluminum [0040] A distance from an interface of a wear-resistant layer [0041] 0 interface of the wear-resistant layer [0042] S aluminizing [0043] t.sub.1-t.sub.3 heat treatment timepoints