ABRADABLE PART FOR AN AIRCRAFT TURBOMACHINE

Abstract

Abradable part (10) for an aircraft turbomachine, this part (10) comprising a support (12) and an abradable coating (14) located on the support, characterized in that the abradable coating (14) comprises at least one fabric (16) made from strand(s) (20) of ceramic fibers (22). Figure for the abstract: Figure 1

Description

Title of the invention: ABRADABLE PART FOR AN AIRCRAFT TURBO-MACHINE Technical field of the invention

[0001] The present invention relates in particular to an abradable part for an aircraft turbomachine and its manufacturing method. Technical background

[0002] Abradable parts are currently used in many parts of gas turbines to minimize as much as possible the functional clearance between the rotating parts and the fixed parts, i.e. between the rotors and the stators.

[0003] In the context of an application in a high pressure or low pressure turbine for example, abradable coatings are deposited on sectors of rings fixed to a stator casing. During rotor / stator contact (i.e. between turbine blades and an abradable part), the abradable coating present on the stator must wear preferentially, which makes it possible to maintain, on the one hand, the aerodynamic performance of the engine, and on the other hand, the integrity of the turbine blades themselves made from expensive materials (for example a monocrystalline nickel-based superalloy).

[0004] However, the extreme physicochemical conditions require the metal support to be protected from high temperatures (up to 1600°C) as well as from oxidation and corrosion. A ceramic or refractory metal-based coating is therefore often sprayed onto the static parts, which are the ring sectors, to form a thermal barrier type protective coating. To date, engine manufacturers favor coatings on the ring sectors that are highly resistant to erosion to the detriment of abradable behavior.

[0005] Feedback from fleets shows significant wear of the blade tips leading to a loss of sealing of the part, but also complex and costly repairs.

[0006] Thermal barrier coatings are primarily designed to protect the support from both the chemical environment (oxidation, corrosion), temperature and mechanical damage (delamination, erosion). They are commonly composed of yttria-containing zirconia produced by plasma spraying (for fixed parts) or by EB-PVD (electron beam physical vapor deposition - for moving parts). Indeed, yttria-containing zirconia has both suitable thermal properties: high chemical stability at temperature, high melting temperature, low thermal conduction for its thermal barrier aspect and coefficient high expansion for a ceramic to avoid delamination problems, but also high mechanical properties (notably toughness). These thermomechanical properties allow it to have good resistance under the conditions of use, for example, good resistance to erosion.

[0007] In the case of coatings on the ring sector of high pressure / low pressure turbines, these thermal barriers must be abradable. Many solutions are proposed today, they concern both the formulation, the structuring and the coating deposition processes.

[0008] Whether on a metallic or CMC (ceramic matrix composite) type support, numerous materials have recently been proposed in the literature for the production of high-temperature ceramic abradables such as materials based on Ln2B2O7 with pyrochlore structures (US-A1-2017 / 0167279A1 - EP-A1-1 367 148), tungsten bronze type (US-A1-2009 / 0258247A1), based on phosphates (EP-A2-0 751 104; EP-B1-0 751 104; US-B1-6,197,474; US-A1-2010 / 0069226; US-A1-2010 / 0151183) or based on rare earth aluminosilicates. (US-A1-2019 / 0093497).

[0009] These matrices, having a lower hardness than the materials currently used to produce the upper layer ("Top-coat"), actually have better abradability properties. However, this lower hardness results in a loss of resistance to erosion. In addition, the addition of lubricating and / or dislocating fillers in different ceramic matrices is also widely proposed. Compounds such as solid lubricants like fluorides (CaF2, MgF2), nitrides (h-BN, TaN, TaN2), borides (HfB2, ZrB2, TaB2, TiB2), carbides (ZrC, Ta2C, NbC) as well as other compounds (MoS2, BC13) have been suggested (US-A-5,434,210; US-A-5,530,050; US-A1-2017 / 0342844; US-A1-2019 / 0093497) as filler in different ceramic matrices applied to thermal or environmental barriers. Nevertheless, the compromises obtained remain insufficient at present.

[0010] One of the key parameters for ensuring both good erosion resistance and good abradability is the control of the microstructure of the coating. Once again, many solutions are proposed, in particular by controlling both the rate, the geometry, the distribution of porosity, or even by managing interparticle bonds.

[0011] For example, yttria zirconia systems with bimodal particle size distribution (micron and submicron) have been proposed (US-A 1-2015 / 0329954; US-A1-2008 / 0167173). The macroscopic porosity ensures abradability while the nanoporous zones ensure erosion resistance.

[0012] A solution based on the management of macroscopic and nanometric porosities by the form factor of the particles has been described by the Applicant in document WO- A1-2020 / 002799.

[0013] Finally, in order to obtain thermal barriers with controlled microstructures, several production processes are proposed in the literature. Conventionally, EB-PVD and plasma spraying processes are mainly used. However, other sintering processes have also been proposed, such as flash sintering (SPS), which firstly allows the production in a single step of multi-layer systems (FR-A1-3 044 945) with a porosity gradient in the abradable layer. However, despite good results, this solution requires special preparation.

[0014] Other solutions consist of starting from a powder with a high form factor, and using partial sintering to obtain a microscopic and micrometric bi-modal porosity ensuring both abradability for the first, and acceptable erosion resistance for the second (WO-A1-2020 / 002799).

[0015] More recently, a hybrid derivative of cold sintering and flash sintering (CSP and SPS), called “Low Temperature Spark Plasma Sintering”, BT-SPS has been proposed, allowing the production of ceramic coatings with an improved erosion resistance / abradability compromise.

[0016] The invention provides an improvement to existing technologies, which is simple, effective and economical. Summary of the invention

[0017] The invention relates to an abradable part for an aircraft turbomachine, this part comprising a support and an abradable coating located on the support, characterized in that the abradable coating comprises at least one fabric made from strand(s) of ceramic fibers.

[0018] The invention thus proposes to use one or more fiber web(s) in the abradable coating, this web or these webs therefore forming part of the abradable coating and therefore being capable of wearing by friction during operation.

[0019] The invention allows the improvement of the erosion resistance / abradability compromise by the presence of one or more fabrics.

[0020] In the case where the fabric(s) are used in combination with one or more other layers of the abradable coating, the or each fabric also makes it possible to improve the adhesion of these layers and therefore the cohesion of the layers between them and of the coating as a whole. In this case, the fabric or one of the fabrics may cover a layer and define a free abradable surface of the coating. The fabric or one of the fabrics may be located inside the coating, for example between two layers or between a layer and the support of the part.

[0021] The device according to the invention may comprise one or more of the characteristics following, taken individually or in combination with each other: • the canvas is a fabric or knit made by weaving the strand(s) of ceramic fibers, or is a non-woven felt composed of the strand(s) of ceramic fibers; • the or each canvas has a thickness between 100 and 900qm; • the or each strand has a diameter between 100 and 600qm; • the fibers which make up the or each strand each have a length of several hundred microns and a diameter of between 50nm and 50qm; • the support is made of metal or ceramic matrix composite; • the fibers are made from a material chosen from yttria-containing zirconia, ytterbium disilicate, yttrium disilicate, and mixtures thereof; • the abradable coating comprises at least one layer of sintered ceramic particles, which covers the fabric or which is covered by the fabric; • the part comprises a layer of particles between two fiber webs, a fiber web between two layers of particles, or a superposition by alternating layers of particles and webs.

[0022] The present invention also relates to an aircraft turbomachine, comprising an abradable part as described above, this part being a casing, a ring or a ring sector, in particular a turbine.

[0023] The present invention also relates to a method of manufacturing an abradable part as described above, characterized in that it comprises the following steps: a. compression of the abradable coating, and b. fixing the abradable coating to the support, step b) occurring during or after step a).

[0024] The method according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:

[0025] - the method comprises, before step a), a step i) of processing the or each canvas, the treatment being chosen from a heat treatment of the or each canvas at a first predetermined temperature, and an impregnation treatment of the or each canvas with a solution comprising ceramic particles or precursors;

[0026] - the abradable part being as defined above, the method comprises, between the steps a) and b), a step ii) of sintering the abradable coating at a second predetermined temperature and under load; and

[0027] - the second temperature is higher than the first temperature. Brief description of the figures

[0028] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0029] [Fig-1] [Fig.l] is a schematic perspective view of an abradable part for an aircraft turbomachine,

[0030] [Fig.2] [Fig.2] is a very schematic of an abradable coating of the part of [Fig.l], according to a first embodiment of the invention,

[0031] [Fig.3] [Fig.3] is seen similar to [Fig.2] and which represents a variant of rea lization of the invention,

[0032] [Fig.4] [Fig.4] is seen similar to [Fig.2] and which represents a variant of rea lization of the invention,

[0033] [Fig.5] [Fig.5] is seen similar to [Fig.2] and which represents another variant of realization of the invention,

[0034] [Fig.6] [Fig.6] is seen similar to [Fig.2] and which represents another variant of realization of the invention,

[0035] [Fig.7] [Fig.7] is seen similar to [Fig.2] and which represents another variant of realization of the invention,

[0036] [Fig.8] [Fig.8] includes microscopic images of ceramic fiber webs of different types,

[0037] [Fig.9] [Fig.9] is a microscopic image of a ceramic fiber,

[0038] [Fig. 10] [Fig. 10] is a very schematic view of a compression machine for sintering an abradable coating,

[0039] [Fig. 11] [Fig. 11] is a microscopic image of an abradable coating and shows the interface between a fabric and a layer of ceramic particles,

[0040] [Fig.l2a-12b] Figures 12a and 12b are graphs showing the evolution of the tem heating temperature of an abradable coating as a function of the penetration depth of an element in this coating, during an experimental test, figure 12a representing the results for an abradable coating without fabric, and figure 12b representing the results for a coating with fabric,

[0041] [Fig.l3a-13b] Figures 13a and 13b are graphs showing the ranges of values of the erosion coefficient of an abradable coating and the maximum wear of an element used for an experimental penetration test in this coating, Figure 13a representing the results for an abradable coating without fabric, and Figure 13b representing the results for a coating with fabric,

[0042] [Fig.l4a-14b] Figures 14a and 14b are graphs showing the evolution of the temperature heating temperature of an abradable coating as a function of the depth of penetration of an element into this coating, during an experimental test, figure 14a representing the results for an abradable coating with several fabrics but without heat treatment, and figure 14b representing the results for a coating with several fabrics and with heat treatment. Detailed description of the invention

[0043] [Fig.l] shows an abradable part 10 for an aircraft turbomachine.

[0044] [Fig. 1] illustrates a non-limiting example of such a part which is here a sector of a turbine ring. In a turbomachine turbine, a wheel comprising blades at its periphery rotates inside a casing which supports bladed turbine distributors arranged respectively upstream and downstream of the wheel with reference to the flow of the gas stream flowing in the turbine.

[0045] The casing further supports a ring which surrounds the wheel and which is sectorized, that is to say formed by several angular sectors arranged end to end. [Fig.l] illustrates one of these sectors.

[0046] The sector or part 10 comprises a support 12 and an abradable coating 14.

[0047] For example, the support 12 is made of metal or ceramic matrix composite.

[0048] In the present application, the term abradable coating 14 means a sacrificial coating capable of wearing easily by friction with an element, without generating wear or damage on the element during friction. In the aforementioned case, the wheel comprises at its periphery at least one annular lip which is capable of coming into contact with the abradable coating 14 and of wearing it by friction by creating for example a groove in this coating.

[0049] A coating 14 has a predetermined thickness E and comprises a surface 14a for connection to the support 12 and an opposite surface 14b which is free and on which the element is likely to rub.

[0050] The invention proposes an improvement to this type of covering, the particularity of which is to have at least one fabric 16 made from strand(s) of ceramic fibers.

[0051] In the present application, the term “strand” means an assembly of several fibers.

[0052] [Fig.2] represents an abradable coating 14 for a part 10 according to the invention. This covering 14 exclusively comprises one or more fabrics 16. The covering 14 therefore comprises a single fabric 16 whose two surfaces respectively define the surfaces 14a, 14b, or else a superposition of two or more fabrics 16, this stack of fabrics comprising a surface forming the connecting surface 14a and another opposite surface forming the abradable surface 14b.

[0053] [Fig. 3] represents an alternative embodiment in which a canvas 16 made from from strand(s) of ceramic fibers, is associated with a layer 18 of sintered ceramic particles.

[0054] The fabric 16 is here interposed between the support 12 and the layer 18. This means that the fabric 16 defines the connecting surface 14a, and the layer 18 defines the abradable surface 14b.

[0055] [Fig.4] represents another variant in which a fabric 16 made from strand(s) of ceramic fibers is associated with a layer 18 of sintered ceramic particles.

[0056] The layer 18 is here interposed between the support 12 and the fabric 16. This means that the layer 18 defines the connecting surface 14a, and the fabric 16 defines the abradable surface 14b.

[0057] [Fig. 5] represents another variant in which a fabric 16 made from strand(s) of ceramic fibers is associated with two layers 18 of sintered ceramic particles.

[0058] The fabric 16 is here interposed between the two layers 18 which respectively define the connecting surface 14a and the abradable surface 14b.

[0059] [Fig.6] represents another variant in which a layer 18 of sintered ceramic particles is associated with two fabrics 16 made from strand(s) of ceramic fibers.

[0060] The layer 18 is here interposed between the two fabrics 18 which respectively define the connecting surface 14a and the abradable surface 14b.

[0061] [Fig.7] represents another variant in which the coating comprises a multitude of layers formed by an alternation of layers 18 of sintered ceramic particles, and of fabrics 16 made from strand(s) of ceramic fibers.

[0062] The connecting surface 14a is defined by one of the strata, therefore by one of the fabrics 16 or one of the layers 18, and the abradable surface 14b is defined by one of the strata, therefore by one of the fabrics 16 or one of the layers 18.

[0063] [Fig.8] shows different types of canvases which can be used in the context of the present invention.

[0064] The fabric 16 may be a woven or knitted fabric made by weaving or knitting the strand(s) of ceramic fibers, or a non-woven felt composed of the strand(s) of ceramic fibers. It is therefore understood that the fabric may be woven, knitted or non-woven, and that in the case of a woven or knitted fabric, several types of weaving or knitting are possible.

[0065] [Fig.8] shows in a) a jersey weave knit for example, which is made by knitting a single strand 20 of ceramic fibers 22.

[0066] [Fig.8] shows in b) and c) fabrics which are made by weaving two strands 20 of ceramic fibers 22. In case b), the fabric has a satin weave whereas in case case c), the fabric has a plain weave.

[0067] [Fig.9] shows a ceramic fiber 22 which is used in the context of the invention.

[0068] The or each canvas 16 preferably has a thickness of between 100 and 900 sqm. The or each strand 20 preferably has a diameter of between 100 and 600 μm. The fibers 22 which make up the or each strand 20 preferably each have a length of several hundred microns and a diameter of between 50 nm and 50 μm.

[0069] The fibers 22 are preferably made of a material chosen from a yttria-containing zirconia, an ytterbium disilicate, an yttrium disilicate, and mixtures thereof.

[0070] Among the possible materials of the particles and fibers, we can cite for example: alumina, mullite, alumina / mullite, silicon or boron nitrides, silicon / boron / or titanium carbides, titanium or nickel aluminides, molybdenum disilicide, lanthanide zirconates of type (Ln2Zr2O7) with fluorite structure Dy2Zr2O7, Er2Zr2O7, Yb2Zr2O7 or pyrochlore Gd2Zr2O7, Sm2Zr2O7, Nd2Zr2O7, La2Zr2O7, etc.

[0071] The present invention also relates to a method for manufacturing an abradable part 10 according to the invention, comprising the following steps: a. compression of the abradable coating 14, and b. fixing the abradable coating 14 to the support 12, step b) occurring during or after step a).

[0072] This method is similar to that described in document WO-A1-2020 / 002799.

[0073] [Fig. 10] schematically illustrates a compression machine 24 for sintering a coating 14 according to the invention. This machine 24 is capable of subjecting the coating 14 to a compression force between two pistons 26 and of heating the coating to a predetermined temperature.

[0074] In practice, the sintering can be of the flash or SPS or BT-SPS type.

[0075] For example, during sintering, the pressure is between 10 and 600 MPa, and is maintained throughout the handling. The temperature is for example between 100 and 2000 °C and the temperature increase ramps are between 10 and 100 °C / min. The duration of the thermal stages can be between 1 and 30 minutes and the temperature of the stage can be lower, equal to or higher than the sintering temperature of the fabrics / knits and / or the powder mixture if present.

[0076] [Fig. 11] is a microscopic image of a sintered coating and shows the interface and cohesion between layer 18 and fabric 16.

[0077] This [Fig.l 1] shows the result of sintering the coating at a temperature of 250°C for 10 minutes under 400 MPa using the BT-SPS process. The pressure applied generates a partial rupture of the fibers that make up the strands. The cohesion between the two layers can be mechanical and / or chemical.

[0078] The method may comprise, before step a), a step i) of treating the or each fabric 16, the treatment being chosen from a heat treatment of the or each fabric 16 at a first predetermined temperature, and an impregnation treatment of the or each fabric 16 with a solution comprising ceramic particles or precursors.

[0079] The impregnation solution may be a slip or a sol loaded with or without inorganic precursors, ideally ceramic particles or precursors, for example yttria-containing zirconia particles or precursors.

[0080] In the case where the abradable part 10 comprises ceramic particles, the method may comprise, between steps a) and b), a step ii) of sintering the abradable coating 14 at a second predetermined temperature and under load. The second temperature is preferably higher than the aforementioned first temperature.

[0081] Figures 12a and 12b are graphs showing the evolution of the heating temperature of an abradable coating as a function of the penetration depth of an element in this coating, during an experimental test. Figure 12a represents the results for an abradable coating without fabric, and Figure 12b represents the results for a coating with fabric.

[0082] Thanks to the presence of a fabric in the coating, on the one hand, a delay in heating is observed and on the other hand, the reduction of the maximum heating temperature. The inventors have also noted that the presence of the fabric in the coating makes it possible to improve the abradable character (absence of bursting of the trace and significantly reduced wear of the blades) while the resistance to erosion remains identical to an architecture without fabric. The compromise between resistance to erosion and abradability is then improved.

[0083] Figures 13a and 13b are graphs showing ranges of values ​​of the erosion coefficient XI of an abradable coating and of the maximum wear X2 of an element used for an experimental test of penetration in this coating. Figure 13a represents the results for an abradable coating without fabric, and Figure 13b represents the results for a coating with fabric,

[0084] It is noted that the erosion coefficient XI is more homogeneous and that the maximum wear X2 of the blade is lower with a coating comprising a fabric.

[0085] Figures 14a and 14b are graphs showing the evolution of the heating temperature of an abradable coating as a function of the penetration depth of an element in this coating, during an experimental test. Figure 14a represents the results for an abradable coating with several fabrics but without heat treatment, and Figure 14b represents the results for a coating with several fabrics and heat treatment.

[0086] It is noted that the heat treatment of the canvases makes it possible to obtain a temperature relatively constant heating regardless of penetration depth during a test.

Claims

Claims

1. Abradable part (10) for an aircraft turbomachine, this part (10) comprising a support (12) and an abradable coating (14) located on the support, characterized in that the abradable coating (14) comprises at least one fabric (16) made from strand(s) (20) of ceramic fibers (22).

2. Abradable part (10) according to claim 1, in which the fabric (16) is a fabric or a knit made by weaving the strand(s) (20) of ceramic fibers (22), or is a non-woven felt composed of the strand(s) (20) of ceramic fibers (22).

3. Abradable part (10) according to one of the preceding claims, in which the or each fabric (16) has a thickness of between 100 and 900 sqm.

4. Abradable part (10) according to one of the preceding claims, in which the or each strand (20) has a diameter of between 100 and 600 sqm.

5. Abradable part (10) according to one of the preceding claims, in which the fibers (22) which make up the or each strand (20) each have a length of several hundred microns and a diameter of between 50nm and 50qm.

6. Abradable part (10) according to one of the preceding claims, in which the support (12) is made of metal or ceramic matrix composite.

7. Abradable part according to one of the preceding claims, in which the fibers (22) are made of a material chosen from a yttria-containing zirconia, an ytterbium disilicate, an yttrium disilicate, and mixtures thereof.

8. Abradable part (10) according to one of the preceding claims, in which the abradable coating (14) comprises at least one layer of sintered ceramic particles (18), which covers the fabric (16) or which is covered by the fabric (16).

9. Abradable part (10) according to claim 8, in which it comprises a layer of particles (18) between two webs (16) of fibers, a web (16) of fibers between two layers of particles (18), or a superposition by alternating layers of particles (18) and webs (16).

10. Aircraft turbomachine, comprising an abradable part (10) according to one of the preceding claims, this part (10) being a casing, a ring or a particular ring sector of turbine.

11. Method for manufacturing an abradable part (10) according to one of the preceding claims, characterized in that it comprises the following steps: a. compression of the abradable coating (14), and b. fixing the abradable coating (14) to the support (12), step b) occurring during or after step a).

12. Method according to claim 11, in which it comprises, before step a), a step i) of treating the or each canvas (16), the treatment being chosen from a heat treatment of the or each canvas (16) at a first predetermined temperature, and an impregnation treatment of the or each canvas (16) with a solution comprising ceramic particles or precursors.

13. Method according to claim 11 or 12, in which, the abradable part (10) being as defined in claim 8 or 9, it comprises, between steps a) and b), a step ii) of sintering the abradable coating (14) at a second predetermined temperature and under load.

14. A method according to any of claims 12 and 13, wherein the second temperature is higher than the first temperature.

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