Patent Application
20210148238
The present invention relates to the general field of protective coatings used to thermally insulate parts in high-temperature environments such as parts used in hot parts of aeronautical or land gas turbine engines.
In order to improve the efficiency of gas turbine engines, in particular high-pressure turbines (HPT) for stationary land-based systems or for aeronautical propulsion, increasingly higher temperatures are being considered. Under these conditions, the materials used, such as metallic alloys or ceramic matrix composites (CMC), require protection, mainly to maintain a sufficiently low surface temperature to ensure their functional integrity and limit their oxidation/corrosion by the surrounding atmosphere.
“Thermal barrier” (TB) or “environmental barrier coating” (EBC) protections are complex multilayer stacks generally consisting of a bond coat allowing protection against oxidation/corrosion deposited on the surface of the base material (metal alloys or composite material) of the substrate, itself topped by a ceramic coating whose primary function is to limit the surface temperature of the coated components. In order to ensure its protection function against oxidation/corrosion and to promote the adhesion of the ceramic coating, the bond coat is preoxidized to form a dense alumina layer on its surface called “thermally grown oxide” (TGO) in the case of thermal barriers. Such protection systems are described in particular in documents D. R. Clarke, M. Oechsner, N. P. Padture, “Thermal-barrier coatings for more efficient gas-turbine engines”, MRS Bulletin, 37, 2012, pp 892-898 and D. Zhu, R. A. Miller, “Thermal and Environmental Barrier Coatings for Advanced Propulsion Engine Systems”, NASA Technical Memorandum, 213129, 2004.
The service life of these systems (TB and EBC) depends on the resistance of the stack to thermal cycling, on the one hand, and on the resistance of the outer layer to environmental stresses (erosion by solid particles, chemical resistance, corrosion, etc.), on the other hand.
In particular, these systems degrade very quickly when exposed to a medium rich in sand or volcanic ash particles (rich in inorganic silica type compounds) commonly known by the generic name CMAS (for oxides of Calcium, Magnesium, Aluminium and Silicon). The infiltration of molten CMAS into a thermal or environmental barrier generally results in degradation by:
To overcome this problem, so-called “anti-CMAS” compositions have been developed, which allow the formation of a waterproof barrier layer by chemical reaction with CMAS as described in document C. G. Levi, J. W. Hutchinson, M. -H. Vidal-Sétif, C. A. Johnson, “Environmental degradation of thermal barrier coatings by molten deposits”, MRS Bulletin, 37, 2012, pp 932-941. The anti-CMAS compositions used will be dissolved in CMAS to form a dense protective phase with a higher melting point than CMAS. In the case of the family of rare-earth zirconates, very promising anti-CMAS materials, this dissolution allows the formation of an apatite phase of type Ca2RE8(SiO4)6O2 (RE=rare earth) which will be blocking but also “parasitic” or secondary phases of the partially stabilized zirconia type (mainly in fluorite form), spinels, or even rare-earth silicates as described in the documents S. Kramer, J. Yang, C. G. Levi, “Infiltration-inhibiting reaction of gadolinium zirconate thermal barrier coatings with CMAS melts”, Journal of the American Ceramic Society, 91, 2008, pp 576-583 and H. Wang, “Reaction mechanism of CaO—MgO—Al2O3—SiO2 (CMAS) on lanthanide zirconia thermal barrier coatings”, PHD Thesis, Auburn University, USA, 2016. However, these secondary phases have volumes and/or thermomechanical or mechanical properties that may reduce the beneficial effect of the anti-CMAS coating.
There is therefore a need for a gas turbine engine part with a CMAS protection layer that confines the CMAS reaction zone to the vicinity of the surface of the protective layer and limits the formation of secondary phases.
The principal aim of the present invention is therefore to increase the reaction capacity or kinetics of a CMAS protection layer to form a layer or phase blocking liquid contaminants in order to limit their deep penetration into the coating by providing a coated gas turbine engine part comprising a substrate and at least one calcium-magnesium-alumino-silicate CMAS protection layer present on said substrate, the layer comprising a first phase of a calcium-magnesium-alumino-silicate CMAS protection material capable of forming an apatite or anorthite phase in the presence of calcium-magnesium-alumino-silicates CMAS and a second phase comprising particles of at least one rare-earth REa silicate dispersed in the first phase.
The addition of a rare-earth silicate phase in divided form in the first phase or matrix phase of the CMAS protection layer increases the reactivity of the latter in order to limit the capillary penetration depth of liquid CMAS within the porosity and/or vertical cracking network present in the layer. Indeed, rare-earth silicates are precursors of the protective apatite phase. The second phase is therefore an “activating” phase of the protective apatite phase. Consequently, the service life of the CMAS protection layer thus obtained is increased compared to that expected for the same protection layer without adding this second phase. In addition, the inclusion of particles of a rare-earth silicate in the base material of the CMAS protection layer allows, during the formation of the blocking phase, to limit the formation of secondary phases with mechanical properties that limit the protective effects of the layer.
According to a particular aspect of the invention, the rare-earth silicate used for the second phase of the protective layer is a rare-earth monosilicate REa2SiO5 or a rare-earth disilicate REa2Si2O7, where REa is selected from: Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutecium).
According to another particular aspect of the invention, the rare-earth REa silicate particles dispersed in the CMAS protection layer have an average size between 5 nm and 50 μm, more preferentially between 5 nm and 1 μm.
According to another particular aspect of the invention, the CMAS protection layer has a volume content of particles of rare-earth silicate of between 1% and 80%.
According to another particular aspect of the invention, the volume percentage of rare-earth REa silicate ceramic particles present in the CMAS protection layer varies in the direction of the thickness of the protective layer, the volume percentage of rare-earth REa silicate ceramic particles gradually increasing between a first zone of said adjacent layer of the substrate and a second zone of said layer remote from the first zone.
According to another particular aspect of the invention, the CMAS protection layer has a thickness between 1 μm and 1000 μm.
According to another particular aspect of the invention, the calcium-magnesium-alumino-silicate CMAS protection material of the first phase capable of forming apatite or anorthite phases corresponds to one of the following materials or a mixture of several of the following materials: rare-earth zirconates REb2Zr2O7, where REb=Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutecium), fully stabilized zirconia, delta phases A4B3O12, where A=Y >Lu and B=Zr, Hf, composites Y2O3 with ZrO2, yttrium and aluminium garnets (YAG), composites YSZ-Al2O3 or YSZ-Al2O3TiO2.
According to another particular aspect of the invention, a thermal barrier layer is interposed between the substrate and the calcium-magnesium-alumino-silicate CMAS protection layer.
According to another particular aspect of the invention, the substrate is made of nickel or cobalt-based superalloy and has an alumino-forming bond layer on its surface.
The invention also relates to a process for manufacturing a gas turbine engine part according to the invention, comprising at least one step of forming a calcium-magnesium-alumino-silicate CMAS protection layer directly on the substrate or on a thermal barrier layer present on the substrate, the forming step being performed with one of the following processes:
Other features and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments without any restrictive character. On the figures:
The invention applies generally to any gas turbine engine part coated with a protective layer comprising a phase of a calcium-magnesium-alumino-silicate CMAS protection material. “CMAS protection material” means all materials which prevent or reduce the infiltration of molten CMAS into the protective layer, in particular by the formation of at least one apatite or anorthite phase.
By way of non-limiting examples, the calcium-magnesium-alumino-silicate CMAS protection material likely to form apatite or anorthite phases corresponds to one of the following materials or a mixture of several of the following materials:
The invention applies more particularly to rare-earth zirconates REb2Zr2O7, where REb=Y, La, Nd, Sm, Gd, Dy, Yb, delta phases with A=Y, Dy or Yb and composite Y2O3ZrO2.
In accordance with the invention, to this first phase, which constitutes the matrix of the CMAS protection layer, is added a second phase in the form of particles of at least one rare-earth RE silicate dispersed in the protective layer whose matrix is formed by the first phase.
The inventors found that rare-earth monosilicates or disilicates are capable of reacting in the presence of CMAS to form an apatite phase, a blocking phase that limits the infiltration depth of liquid CMAS into the protective layer, without being dissolved in the liquid glass. The inventors have therefore determined that the addition in the form of a rare-earth monosilicate and/or disilicate filler dispersed in a CMAS protection material constitutes an “activating” phase for the formation of apatite phases. By thus exacerbating the reactivity of the CMAS protection material with fillers distributed in the CMAS protection material, it is possible to form blocking phases for liquid CMAS by using different reaction mechanisms, the formation of the blocking phases being generated independently between the CMAS protection material of the first phase and the rare-earth silicate particles of the second phase. This limits the infiltration of liquid CMAS into the volume of the material. Therefore, by limiting the depth of CMAS infiltration into the protective layer, changes in thermomechanical properties or volumes resulting from the formation of blocking phases, as well as secondary phases resulting from the dissolution of the CMAS protection material, are limited. The mechanical stresses at the core of the protective layer are also reduced, which increases the service life of the protection under operating conditions.
The particles dispersed in the matrix or first phase of the CMAS protection layer may consist of a REa2SiO5 rare-earth monosilicate or a REa2Si2O7 rare-earth disilicate, where REa is selected from: Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutecium). More preferably, the rare earth REa of the rare-earth monosilicate REa2SiO5 or of the rare-earth disilicate REa2Si2O7, is chosen from: La, Gd, Dy, Yb, Y, Sm, Nd.
The second “activating” phase for the formation of apatite phases present as particles dispersed in the CMAS protection layer can be obtained from powders, suspensions, precursors in solution or a combination of these different forms.
The rare-earth REa silicate particles dispersed in the first phase preferably have an average size between 5 nm and 50 μm and preferentially between 5 nm and 1 μm. In the present disclosure, the terms “between . . . and . . . ” are to be understood as including the boundaries.
The protective layer has a volume content of rare-earth silicate particles which can be between 1% and 80%, preferentially between 1% and 30%.
The protective layer may have a composition gradient wherein the volume percentage of the first phase of the anti-CMAS material and the second phase of rare-earth silicate particles changes with the thickness of the protective layer. More precisely, the volume percentage of rare-earth REa silicate ceramic particles present in the CMAS protection layer can vary with the thickness of the protective layer, the volume percentage of rare-earth REa silicate ceramic particles gradually increasing between a first zone of said layer adjacent to the substrate and a second zone of said layer remote from the first zone. By introducing such a gradient in the content of rare-earth REa silicate particles into the protective layer, the reactivity and the CMAS-resistance effect is favoured in the vicinity of the upper surface of the protective layer by a high concentration of rare-earth silicate at this location of said protection layer while preserving the thermomechanical resistance of the system by a lower concentration of rare-earth silicate in the protective layer near the substrate. Rare-earth silicate has a low coefficient of thermal expansion that can reduce the strength of the protective layer in the vicinity of the substrate, as the differences in coefficient of expansion between the rare-earth silicate and the substrate material are significant.
The protective layer preferably has a porous structure, which allows it to have good thermal insulation properties. The protective layer may also have vertical cracks, initially present in the layer or formed during use, which give the layer a higher deformation capacity and therefore a longer service life. The porous and cracked microstructure (initially or in use) of the protective layer is mainly obtained by controlling the forming (deposition) process of the layer as well known per se.
Thanks to the presence of a second “activating” phase in the protective layer allowing the formation of blocking phases for liquid CMAS in the vicinity of the layer surface, these porosities and cracks no longer constitute favoured paths for the infiltration of molten CMAS as in the prior art. The effectiveness of the CMAS protection material used in the first phase is thus preserved.
In the case of a protective layer according to the prior art as shown in
In a different way, in the case of a protective layer according to the invention as shown in
The calcium-magnesium-alumino-silicates CMAS protection layer according to the invention has a thickness between 1 μm and 1000 μm and preferentially between 5 μm and 200 μm.
The substrate of the gas turbine engine part that is the subject matter of the invention can be made of a nickel or cobalt-based superalloy. In this case, the substrate may also have an alumino-forming bond coat on its surface. For example, the alumino-forming bond coat may include MCrAlY alloys (where M=Ni, Co, Ni and Co), nickel aluminides type β-NiAl (optionally modified by Pt, Hf, Zr, Y, Si or combinations of these elements), aluminides of alloys γ-Ni-γ′Ni3Al (optionally modified by Pt, Cr, Hf, Zr, Y, Si or combinations of these elements), MAX phases (Mnn+1AXn (n=1,2,3) where M=Sc, Y, La, Mn, Re, W, Hf, Zr, Ti; A=groups IIIA, IVA, VA, VIA; X=C,N), or any other suitable bond coat, as well as mixtures thereof. The substrate can also consist of superalloys AM1, MC-NG, CMSX4 and derivatives, or René and derivatives.
Bond layers can be formed and deposited by physical vapour deposition (PVD), APS, HVOF, low-pressure plasma spraying (LPPS) or derivatives, inert plasma spraying (IPS), chemical vapour deposition (CVD), Snecma vapour-phase aluminizing (SVPA), spark plasma sintering, electrolytic deposition, as well as any other suitable deposition and forming process.
The substrate used in the invention has a shape corresponding to that of the gas turbine engine part to be made. Turbomachine parts including the protective layer according to the invention may be, but not exclusively, blades, nozzle vanes, high-pressure turbine rings and combustion chamber walls.
The composite calcium-magnesium-alumino-silicate protection layer, i.e. comprising the first and second phases as defined above, can be applied directly to the substrate of the gas turbine engine part. The protective layer of the invention constitutes in this case a thermal barrier for the substrate.
According to a variant embodiment, a thermal barrier layer may be interposed between the substrate and the composite protection layer of the invention, or between an alumino-forming bond coat and the composite protection layer of the invention, the latter being used in this case as a functionalization layer on the surface of the thermal barrier layer which may or may not provide protection against high-temperature liquid calcium-magnesium-alumino-silicate CMAS contaminants. By way of non-limiting example, the thermal barrier layer can be made of yttriated zirconia with a Y2O3 mass content of between 7% and 8%. The thermal barrier layer, on which the composite protection layer of the invention is made, may have a microstructure, homogeneous, homogeneous and porous, vertically microcracked, vertically microcracked and porous, columnar, columnar and porous, as well as architectures including these different microstructures.
The thermal barrier layer can be formed and deposited by electron beam-physical vapour deposition (EBPVD), APS, HVOF, solgel, SPS, solution precursor plasma spraying (SPPS), HVSFS or any other suitable process.
The composite protection layer of the invention may be formed and deposited by one of the following processes:
As shown in
In this example, a solution 40 containing a powder of the anti-CMAS material in suspension 42, here Gd2Zr2O7, and liquid precursors of the activating phase 41, here Y2Si2O7, in volume proportions adapted for the realization of the protective layer 32 is used. The solution 40 is injected through the same suspension injector 42 into a plasma jet 44 generated by a plasma torch 43, allowing the thermokinetic treatment of the solution 40. In this example, the precursors of phase Y2Si2O7 may be yttrium nitrate Y(NO3)3 and tetraethyl orthosilicate Si(OC2H5)4 dissolved in ethanol. This results in a protective layer 32 comprising a first phase of Gd2Zr2O7 as anti-CMAS material and forming the matrix of the layer 32 and a second phase of Y2Si2O7 as activator of protective apatite phases in the form of particles finely dispersed in the matrix of the layer 32.
The example does not exclude the possibility of using other anti-CMAS materials or other silicate materials. The example also does not exclude the use of a precursor solution for the anti-CMAS phase and/or suspended powders for the silicate phase. It is also possible to produce the composite coating by using not a plasma torch but an HVOF device.
As shown in
In this example, a first solution 61 containing a powder of the anti-CMAS material in suspension 610, here Gd2Zr2O7, and a second solution 62 containing liquid precursors of the activating phase 620, here Y2Si2O7, in volume proportions adapted for the realization of the protective layer 52 are used. The two solutions 61 and 62 are injected through the same suspension injector 63 into a plasma jet 64 generated by a plasma torch 65, allowing the thermokinetic treatment of the solutions 61 and 62. In this example, the precursors of phase Y2Si2O7 may be yttrium nitrate Y(NO3)3 and tetraethyl orthosilicate Si(OC2H5)4 dissolved in ethanol. The example does not exclude the possibility of using other anti-CMAS materials or other silicate materials. This results in a protective layer 32 comprising a first phase of Gd2Zr2O7 as anti-CMAS material and forming the matrix of the layer 32 and a second phase of Y2Si2O7 as activator of protective apatite phases in the form of particles finely dispersed in the matrix of the layer 32.
The example also does not exclude the use of a precursor solution for the anti-CMAS phase and/or suspended powders for the silicate phase. It is also possible to produce the composite coating by using not a plasma torch but an HVOF device.
As shown in
In this example, a first solution 81 containing a powder of the anti-CMAS material in suspension 810, here Gd2Zr2O7, and a second solution 82 containing liquid precursors of the activating phase 820, here Y2Si2O7, in volume proportions adapted for the realization of the protective layer 72 are used. The solutions 81 and 82 are injected respectively through a first and a second specific suspension injectors 83 and 84 into the core of a plasma jet 85 generated by a plasma torch 86, allowing the thermokinetic treatment of the solutions 81 and 82. In this example, the precursors of phase Y2Si2O7 may be yttrium nitrate Y(NO3)3 and tetraethyl orthosilicate Si(OC2H5)4 dissolved in ethanol. This results in a protective layer 32 comprising a first phase of Gd2Zr2O7 as anti-CMAS material and forming the matrix of the layer 32 and a second phase of Y2Si2O7 as activator of protective apatite phases in the form of particles finely dispersed in the matrix of the layer 32.
The example does not exclude the possibility of using other anti-CMAS materials or other silicate materials. The example also does not exclude the use of a precursor solution for the anti-CMAS phase and/or suspended powders for the silicate phase. It is also possible to produce the composite coating by using not a plasma torch but an HVOF device.
As shown in
In this example, a powder 110 composed of particles 111 of the anti-CMAS material, here Gd2Zr2O7, and a solution 120 containing liquid precursors of the activating phase 121, here Y2Si2O7, in volume proportions adapted for the realization of the protective layer 92 are used. For the powder 110, the APS process is used, whereby the powder 110 is injected through a first specific injector 101 into the core of a plasma jet 103 generated by a plasma torch 104, allowing the thermokinetic treatment of the powder 110. For the solution 120, the SPS process is used wherein the solution 120 is injected through a second specific suspension injector 102 into the core of the plasma jet 103 generated by a plasma torch 104, allowing the thermokinetic treatment of phase 121. In this example, the precursors of phase Y2Si2O7 may be yttrium nitrate Y(NO3)3 and tetraethyl orthosilicate Si(OC2H5)4 dissolved in ethanol. This results in a protective layer 32 comprising a first phase of Gd2Zr2O7 as anti-CMAS material and forming the matrix of the layer 32 and a second phase of Y2Si2O7 as activator of protective apatite phases in the form of particles finely dispersed in the matrix of the layer 32.
The example does not exclude the possibility of using other anti-CMAS materials or other silicate materials. The example also does not exclude the use of a precursor solution for the anti-CMAS phase and/or suspended powders for the silicate phase. It is also possible to produce the composite coating by using not a plasma torch but an HVOF device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1755211 | Jun 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/051349 | 6/11/2018 | WO | 00 |
