Patent Application
20230127445
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 102021127344.7, filed Oct. 21, 2021, the entire disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for coating a component of an aircraft engine with a wear-resistant layer, to a method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine, to a method for producing a wear-resistant layer on a component of an aircraft engine, to a component for an aircraft engine that is provided at least regionally with a wear-resistant layer, and to an aircraft engine which comprises at least one such component.
Vibration and friction at contact points between components in aircraft engines cause wear. To protect the base material of the individual components from this wear, thermally sprayed wear-resistant layers are frequently applied. An example of a typical wear-resistant layer is a thermally sprayed Tribaloy T800 layer. This layer, which can be used at up to 900° C., comprises a cobalt-based powder which is applied typically by high-velocity flame spraying (HVOF). It is likewise known practice to use nickel-based powders in order to produce such wear layers.
The service temperatures of wear-resistant layers are limited due to oxidation at high temperatures. Where the layers are employed above the stated temperature of around 900° C., they suffer severe oxidation and protection from wear is no longer provided for the base material of the component. An attack on the base material leads subsequently to premature repair or to a need for the component to be replaced. Future engine programs are aiming at ever higher temperatures in order to achieve the required efficiency. As a result of this, wear-resistant layers are needed which can be employed reliably even at temperatures above 900° C.
In view of the foregoing, it would be advantageous to be able to provide a method for coating a component of an aircraft engine with a wear-resistant layer, a method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine, a method for producing a wear-resistant layer on a component of an aircraft engine, a component for an aircraft engine that is provided at least regionally with a wear-resistant layer, and an aircraft engine which comprises at least one such component, where the respective wear-resistant layers can be employed reliably even at temperatures above 900° C.
The present invention provides a method for coating a component of an aircraft engine with a wear-resistant layer, a method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine, a method for producing a wear-resistant layer on a component of an aircraft engine, a method for producing a wear-resistant layer on a component of an aircraft engine, a component which is provided at least regionally with a wear-resistant layer, and an aircraft engine which comprises one such component, each as set forth in the independent claims. Advantageous embodiments with useful developments of the invention are specified in the respective dependent claims; advantageous embodiments of each aspect of the invention are deemed to be advantageous embodiments of the other aspects of the invention.
A first aspect of the invention relates to 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. In other words, in the invention, aluminum or an aluminum alloy is introduced subsequently into the wear-resistant layer, and protects the wear-resistant layer from oxidation by means of aluminum incorporated by diffusion. In the context of the present disclosure, the term “aluminum” shall always be deemed to encompass “aluminum alloys” as well. Aluminizing in the context of the present disclosure refers to the accumulation of aluminum in the wear-resistant layer, which thereafter is better protected from high-temperature oxidation and also against attack by other elements and can therefore be operated reliably even at temperatures above 900° C. The accumulation of the aluminum may be only superficial or may penetrate more deeply into the wear-resistant layer. At the extreme, the aluminum is present at least in substantially uniform distribution in the wear-resistant layer. In general “a/an” in the context of this disclosure should be read as indefinite articles, i.e., always also as “at least one” unless expressly indicated otherwise. Conversely, “a/an” may also be understood as “only one”.
In one advantageous embodiment, the nickel- or cobalt-based alloy is aluminized by gas-phase aluminizing and/or by slip aluminizing and/or powder pack aluminizing. In other words, the aluminum may be introduced into the wear-resistant layer by way of a gas-phase operation, such as chemical vapor deposition (CVD), and/or by way of a slip process. As a result, the wear-resistant layer can be aluminized optimally as a function of the geometry and base material of the component.
In a further advantageous embodiment of the method of the invention, the wear-resistant layer after the aluminizing is subjected to heat treatment. This allows the distribution of the aluminum within the wear-resistant layer to be adjusted in a targeted way, since the aluminum diffuses into the interior of the wear-resistant layer as a result of the heat treatment. It may further be assumed that in the operation of the wear-resistant layer, at high temperatures in an aircraft engine, a relatively homogeneous distribution of the aluminum is established over time after a certain time. As a result of a targeted heat treatment, this condition can be produced from the outset, so that the properties of the wear-resistant layer in later operation are no longer subject, at least substantially, to any change, even if at high temperatures there is interdiffusion with the base material, which may have a different chemical composition than the wear-resistant layer. The heat treatment may additionally cause alteration to the structure and the microstructure of the wear-resistant layer. A heat treatment in the context of the present disclosure refers to a method for treating the component provided with the wear-resistant layer, wherein at least the wear-resistant layer or the entire component is subjected to controlled heating and cooling again.
In a further advantageous embodiment of the invention, the heat treatment comprises diffusion annealing, which is especially suitable for reducing microstructural inhomogeneities. Alternatively or additionally it is provided that the heat treatment is carried out at pressure reduced relative to standard pressure and/or under protective gas atmosphere. In this way it is possible in particular to control the oxygen content and to prevent unwanted oxidation.
Further advantages arise when the nickel- or cobalt-based alloy, after application to the component and before the aluminizing, is at least regionally nickel-plated. By means of preferably electrochemical nickel-plating of the wear-resistant layer, the diffusion of the aluminum into the layer can be promoted. In the case of nickel-based alloys, this step is frequently not necessary, but is nevertheless useful in certain cases.
In a further advantageous embodiment of the invention, the nickel- or cobalt-based alloy is selected from CoMoCrSi alloys, more particularly T800, NiMoCrSi alloys, and CoCrWNi alloys. This allows the advantages of the wear-resistant layer produced in accordance with the invention to be realized for alloys that are commonplace and established in engine construction.
In one embodiment of the invention the nickel- or cobalt-based alloy is CoMoCrSi alloy, namely T800, with 27-30 wt % Mo, 16.5-18.5 wt % Cr, 3-3.8 wt % Si, and the balance Co and unavoidable impurities. These unavoidable impurities may comprise up to 1.7 wt % per constituent, up to 3.5 wt % in total, and/or may comprise the constituents Fe, Ni, O, C, P, and S. The Mo constituent in this case may introduce hardness and tribooxides for advantageous wear protection.
In one embodiment of the invention the nickel- or cobalt-based alloy is a NiMoCrSi alloy, namely T700, with 31-34 wt % Mo, 14.5-16.5 wt % Cr, 3-3.8 wt % Si, and the balance Ni and unavoidable impurities. These unavoidable impurities may comprise up to 3.2 wt % per constituent, up to 4.1 wt % in total, and/or may comprise the constituents Fe, Co, O, C, P, and S. The Mo constituent in this case may introduce hardness and tribooxide for advantageous wear protection.
In one embodiment of the invention the nickel- or cobalt-based alloy is a CoCrWNi alloy, with 24.5-26.5 wt % Cr, 6.5-8.0 wt % W, 9.5-11.5 wt % Ni, 0-0.6 wt % C, more particularly 0.42-0.55 wt % C, and the balance Co and unavoidable impurities. These unavoidable impurities may comprise up to 2.2 wt % per constituent, up to 4.5 wt % in total, and/or may comprise the constituents Fe, Mn, Si, P, and S. The W constituent in this case may introduce hardness for advantageous wear protection.
A second aspect of the invention relates to a method for producing spray powder for producing a wear-resistant layer of a component of an aircraft engine, wherein a nickel- or cobalt alloy is provided, admixed with aluminum and/or an aluminum alloy, and jointly melted and/or atomized. This represents an advantageous possibility for providing a spray powder which is suitable for producing a temperature-stable and oxidation-resistant wear-resistant layer comprising an aluminum-containing or aluminized nickel- or cobalt-based alloy. The joint atomization and/or melting ensures that the aluminum is present in relatively uniform distribution in the powder from the outset, meaning that a wear-resistant layer produced using the spray powder likewise has a relatively uniform distribution of aluminum from the outset. Further features and their advantages are apparent from the descriptions of the first aspect of the invention.
A third aspect of the invention relates to a method for producing a wear-resistant layer on a component of an aircraft engine, wherein a first powder composed of a nickel- or cobalt-based alloy is mixed with a second powder composed of aluminum and/or aluminum alloy, after which the first and second powders are thermally sprayed at least onto a region of the component, in order to produce the wear-resistant layer. This represents a further advantageous alternative for the production of a temperature-stable and oxidation-resistant wear-resistant layer composed of an aluminum-containing or aluminized nickel- or cobalt-based alloy. The first and second powders are preferably sprayed simultaneously if homogeneous mixing is desired. Alternatively the first and second powders may be sprayed successively or in temporally varying proportions in order to achieve a defined aluminum distribution in the wear-resistant layer. Further features and their advantages are apparent from the descriptions of the preceding aspects of the invention.
A fourth aspect of the invention relates to a method for producing a wear-resistant layer on a component of an aircraft engine, wherein a composite powder composed of a first powder which consists of a nickel- or cobalt-based alloy and of a second powder which consists of aluminum and/or aluminum alloy is produced, after which the composite powder is thermally sprayed at least onto a region of the component, in order to produce the wear-resistant layer. This represents a further advantageous alternative for producing a temperature-stable and oxidation-resistant wear-resistant layer composed of an aluminum-containing or aluminized nickel- or cobalt-based alloy. The composite powder may consist generally of loose and/or mutually adhered powder particles. Rather than the use of two different powders, a composite powder is used which is sprayed as one component, in order to produce the aluminized wear-resistant layer. In this way, particularly uniform distribution of the aluminum in the wear-resistant layer can be ensured. Further features and their advantages are apparent from the descriptions of the preceding aspects of the invention.
A fifth aspect of the invention relates to a component for an aircraft engine, provided at least regionally with a wear-resistant layer. In accordance with the invention the wear-resistant layer consists of an aluminized nickel- or cobalt-based alloy. The wear-resistant layer allows the component to be used reliably in an aircraft engine even at temperatures above 900° C. Further features and their advantages are apparent from the descriptions of the preceding aspects of the invention.
A sixth aspect of the invention relates to an aircraft engine which comprises at least one component according to the fifth aspect of the invention and/or which comprises at least one component that has a wear-resistant layer which is produced in accordance with the first aspect of the invention and/or which is generated from a spray powder produced in accordance with the second aspect of the invention and/or which is produced by means of a method according to the third or fourth aspects of the invention. This allows the component to be used reliably in the aircraft engine even at temperatures above 900° C., endowing the aircraft engine with enhanced efficiency. Further features and their advantages are apparent from the descriptions of the preceding aspects of the invention.
Further features of the invention are apparent from the claims, the FIGURES, and the description of the figures. The features and feature combinations stated above in the description, and also the features and feature combinations stated hereinafter in the description of the FIGURES, and/or shown alone in the FIGURE, can be used not only in the particular combination indicated, but also in other combinations, without departing the scope of the invention. It is therefore the case that the invention is also deemed to encompass and disclose embodiments which are not explicitly shown and elucidated in the FIGURE, are nevertheless consequent upon and can be generated by separate feature combinations from the embodiments elucidated. Also considered to be disclosed are embodiments and feature combinations which, accordingly, do not have all of the features of an originally formulated independent claim. The disclosure is additionally deemed to encompass embodiments and feature combinations, especially by virtue of the embodiments set out above, which go beyond or deviate from the feature combinations set out in the dependency references of the claims. The single FIGURE shows a diagram of the distribution of aluminum in a wear-resistant layer of a component of an aircraft engine as a result of diffusion at different times.
In the drawing,
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.
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 t1, t2, and t3. 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.
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.
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.
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.
1. Gas-Phase Aluminizing
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 t2); 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 t1). 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 t3.
2. Slip Aluminizing
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.
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.
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.
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 (t3).
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021127344.7 | Oct 2021 | DE | national |
