FUSED SAND-RESISTANT AERONAUTICAL PART

Abstract

The invention relates to an aeronautical part, such as, for example, a turbine blade or a distributor vane, which is used in aeronautics, comprising at least one reactive layer adapted to react with at least one CMAS compound, the reactive layer at least partially covering the environmental barrier, characterized in that the material of the reactive layer comprises at least one oxide of the formula A′4-xA″xB′2-yB″yO11-δ, A′ being selected from a rare earth, yttrium and scandium, A″ being selected from a rare earth, yttrium, scandium and aluminum, B′ being selected from tantalum and niobium, B″ being selected from tantalum, niobium, titanium, zirconium, hafnium, aluminum and cesium, wherein x and y are real numbers between 0 and 2 and δ is a real number between −1 and 2 and preferably between −1 and 1.

Claims

1. An aeronautical part, comprising a substrate, an environmental barrier and at least one reactive layer, the environmental barrier comprising at least one layer selected from a thermally insulating layer, a sublayer suitable for promoting adhesion between the substrate and the thermally insulating layer and a protective layer suitable for protecting the substrate from oxidation and/or corrosion, the environmental barrier at least partially covering the substrate, the at least one reactive layer being suitable for reacting with at least one CMAS compound selected from a calcium oxide, a magnesium oxide, an aluminum oxide and a silicon oxide, the reactive layer at least partially covering the environmental barrier, wherein the material of the reactive layer comprises at least one oxide of formula A′.sub.4-xA″.sub.xB′.sub.2-yB″.sub.yO.sub.11-δ, A′ being selected from a rare earth, yttrium and scandium, A″ being selected from a rare earth, yttrium, scandium and aluminum, B′ being selected from tantalum and niobium, B″ being selected from tantalum, niobium, zirconium, hafnium, aluminum and cesium, x and y being real numbers between 0 and 2 and δ being a real number between −1 and 1.

2. The aeronautical part as claimed in claim 1, wherein the oxide predominantly has a cubic lattice in volume.

3. The aeronautical part as claimed in claim 1, wherein the oxide has a rare-earth atomic fraction of between 18% and 24%.

4. The aeronautical part as claimed in claim 1, wherein A′ and A″ are the same element, A′ and A″ being selected from a rare earth, scandium and yttrium.

5. The aeronautical part as claimed in claim 1, wherein B′ and B″ are the same element, B′ and B″ being selected from tantalum and niobium.

6. The aeronautical part as claimed in claim 1, wherein the reactive layer directly overlies a layer selected from the thermally insulating layer and the protective layer.

7. The aeronautical part as claimed in claim 1, wherein the reactive layer has a thickness of between 5 μm and 500 μm.

8. The part as claimed in claim 1, wherein the reactive layer comprises at least 50% by volume of said oxide.

9. The aeronautical part as claimed in claim 1, wherein the reactive layer also comprises at least one complementary oxide selected from yttriated zirconia, Al.sub.2O.sub.3, Y.sub.2O.sub.3—ZrO.sub.2—Ta.sub.2O.sub.5 and an oxide of formula C.sub.2D.sub.2O.sub.7, wherein C is selected from a rare earth and yttrium and D is selected from zirconia and silicon.

10. The aeronautical part as claimed in claim 1, wherein the average volume fraction of said oxide in the reactive layer varies with increasing distance from the substrate.

Description

DESCRIPTION OF THE FIGURES

[0038] Other features, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which should be read in conjunction with the appended drawings in which:

[0039] FIG. 1 schematically illustrates a cross-section of a turbine part, for example a turbine blade or a nozzle vane,

[0040] FIG. 2 is a microphotograph illustrating a cross-section of substrate covered with an environmental barrier,

[0041] FIG. 3 is a microphotograph illustrating the insertion of molten CMAS compounds into the environmental barrier,

[0042] FIG. 4 is a microphotograph illustrating the insertion of molten CMAS compounds into the environmental barrier,

[0043] FIG. 5 is a microphotograph illustrating the breakdown of an environmental barrier,

[0044] FIG. 6 is a microphotograph illustrating the breakdown of an environmental barrier,

[0045] FIG. 7 schematically illustrates a turbine part comprising a coating according to the invention,

[0046] FIG. 8 schematically illustrates a turbine part comprising a coating according to the invention, in contact with CMAS compounds,

[0047] FIG. 9 schematically illustrates a turbine part comprising a coating according to the invention.

[0048] Throughout the figures, similar elements have identical reference marks.

Definitions

[0049] The term “superalloy” refers an alloy that, at high temperature and high pressure, has very good resistance to oxidation, corrosion, creep and cyclic stresses (particularly mechanical or thermal stresses). Superalloys have a particular application in the manufacture of parts used in aeronautics, for example turbine blades, because they constitute a family of high-strength alloys that can work at temperatures relatively close to their melting points (typically 0.7 to 0.8 times their melting temperatures).

[0050] A superalloy may have a two-phase microstructure comprising a first phase (referred to as “γ phase”) forming a matrix, and a second phase (referred to as “γ′ phase”) forming precipitates hardening in the matrix. The coexistence of these two phases is referred to as γ-γ′ phase.

[0051] The “base” of the superalloy refers to the main metal component of the matrix. In most cases, superalloys comprise an iron, cobalt or nickel base, but sometimes also a titanium or aluminum base. The base of the superalloy is preferentially a nickel base.

[0052] “Nickel-base superalloys” have the advantage of offering a good compromise between oxidation resistance, high-temperature fracture resistance and weight, which justifies their use in the hottest parts of turbojet engines.

[0053] Nickel-base superalloys consist of a γ phase (or matrix) of the face-centered cubic austenitic γ-Ni type, optionally containing substitutional solid solution additives α (Co, Cr, W, Mo), and a γ′ phase (or precipitates) of the γ′-Ni.sub.3X type, with X=Al, Ti or Ta. The γ′ phase has an ordered L12 structure, derived from the face-centered cubic structure, consistent with the matrix, i.e., having an atomic lattice very close to it.

[0054] The term “volume fraction” refers to the ratio of the volume of an element or group of elements to the total volume.

[0055] “Space group” of a crystal refers to the set of symmetries of a crystal structure, i.e., the set of affine isometries leaving the structure invariant. It is a group in the mathematical sense of the term.

DETAILED DESCRIPTION OF THE INVENTION

[0056] With reference to FIG. 7, a part 1 comprises a substrate 2. The substrate 2 may preferentially be a superalloy substrate, and preferably a nickel-base superalloy as described above. The substrate 2 is at least in partially covered by an environmental barrier 3. The environmental barrier 3 may comprise, in a known manner, and as illustrated in FIG. 1, a sublayer 4 extending between the substrate 2 and the other layers of the environmental barrier 3, directly overlying the substrate 2, suitable for promoting adhesion between the substrate 2 and the other layers of the environmental barrier 3. The environmental barrier 3 may also comprise a protective layer 5, suitable for protecting the substrate 2 from oxidation and/or corrosion, and directly covering the sublayer 4. The protective layer 5 is for example formed by oxidation of the sublayer 4. It may for example be made of alumina. The environmental barrier 3 may also comprise a thermally insulating layer 7, directly covering the protective layer 5.

[0057] The part 1 also comprises a reactive layer 9 suitable for reacting with at least one CMAS compound 8. The CMAS compound 8 may be a calcium oxide, a magnesium oxide, an aluminum oxide and/or a silicon oxide. The reactive layer 9 at least partially covers the environmental barrier 3. It may directly cover at least one of the layers of the environmental barrier 3, selected from the protective layer 5 and the thermally insulating layer 7. Different reactive layers 9 may also cover different layers of the environmental barrier 3. The embodiment illustrated in FIG. 1 comprises at least one reactive layer 9 covering all of the layers of the environmental barrier 3. The reactive layer 9 may have a thickness between 5 μm and 500 μm, so as to allow the formation of an apatite phase upon contact with a CMAS compound 8.

[0058] The material of the reactive layer 9 comprises an oxide of formula A′.sub.4-xA″.sub.xB′.sub.2-yB″.sub.yO.sub.11-δ, A′ being selected from a rare earth and yttrium, A″ being selected from a rare earth, yttrium, aluminum and scandium, B′ being selected from tantalum and niobium, B″ being selected from tantalum, niobium, titanium, zirconium, hafnium, aluminum and cesium, x and y being real numbers between 0 and 2 and 6 being a real number between −1 and 2, and preferentially between −1 and 1. This formula allows the oxide of the reactive layer 9 (hereinafter “the oxide”) to predominantly have a cubic lattice in volume. Thus, the material of the reactive layer 9 comprises a volume fraction of rare earth and/or yttrium high enough to allow a rapid precipitation of the molten CMAS compound(s), and to avoid their introduction into interstices present in the environmental barrier 3. Concomitantly, the oxide, by virtue of its composition, predominantly has a cubic lattice in volume, which allows it to have a high atomic fraction of rare earths and/or yttrium. Table 1 comprises the various elements A′, A″, B′ and B″ which can be selected for the oxide.

TABLE-US-00001 TABLE 1 A′ A″ B′ B″ Sc, Y, La, Sc, Y, La, Ta, Nb, Ta, Nb Ce, Pr, Ce, Pr, Ti, Zr, Nd, Pm, Nd, Pm, Hf, Al, Ce Sm, Eu, Sm, Eu, Gd, Tb, Gd, Tb, Dy, Ho, Dy, Ho, Er, Tm, Er, Tm, Yb, Lu Yb, Lu, Al

[0059] Thus, the oxide material may have a rare earth and/or yttrium atomic fraction between 18% and 24%. This range of rare earth and/or yttrium atomic fraction, higher than that of Gd.sub.2Zr.sub.2O.sub.7 for example, allows the material of the reactive layer 9 to exhibit faster reaction kinetics with the CMAS compound(s) 8 than materials described in the prior art (for example Gd.sub.2Zr.sub.2O.sub.7). Thus, the molten CMAS compound(s) 8 in contact with the reactive layer 9 are immobilized more quickly, or slowed down by a production of an apatite phase, thickening and/or solidifying the reactive CMAS compound 8 at the interface with the environmental barrier 3, and avoiding contact between the CMAS compound(s) 8 and other parts of the environmental barrier 3.

[0060] Advantageously, the elements A′ and A″ may be different. Thus, the reactivity of the oxide with respect to the at least one CMAS 8 can be increased by the formation of different phases, including at least one apatite phase, for example of the general formula Ca.sub.2RE.sub.8(SiO.sub.4).sub.6O.sub.2, RE being a rare earth or yttrium. Y.sub.2Gd.sub.2Ta.sub.2O.sub.11 and Y.sub.2Yb.sub.2Ta.sub.2O.sub.11 are examples of compositions used for the oxide, wherein A′ and A″ are different elements.

[0061] Advantageously, the elements B′ and B″ can be different. Thus, the mechanical properties of the oxide can be adjusted. For example, the mechanical strength can be higher. Gd.sub.4Ta.sub.1.5Zr.sub.0.5O.sub.10.75, Gd.sub.4Nb.sub.1.5Zr.sub.0.5O.sub.10.75, La.sub.4Ta.sub.1.5Hf.sub.0.5O.sub.10.75 are examples of compositions used for the oxide, wherein B′ and B″ are different elements.

[0062] Advantageously, the elements A′, A″, B′ and B″ are selected so as to allow the formation of an apatite phase and an anorthite phase when the oxide and a CMAS compound 8 are in contact. The apatite phase and the anorthite phase are then blocking or sealing with respect to the CMAS compounds 8. In addition, the reactivity of the oxide with respect to the CMAS compounds 8 may be increased. Preferentially, A′ and/or B′ are aluminum. Due to the volume fraction of aluminum in the reactive layer 9, the CMAS compound 8 can be locally enriched in aluminum oxide and be more easily crystallizable. La.sub.3AlTaAlO.sub.10, Gd.sub.3.1Al.sub.0.9Ta.sub.1.7Ti.sub.0.3O.sub.10.85 are examples of compositions that can form both an apatite phase and an anorthite phase in contact with a CMAS compound 8.

[0063] Advantageously, the elements A′, A″, B′ and B″ are selected so as to allow the formation of a secondary oxide, resulting from the reaction between the oxide and the CMAS compound(s) 8. The secondary oxide formed is reactive with by-products of the reaction between the oxide and the CMAS compound(s) 8, such as Ta.sub.2O.sub.5 or Nb.sub.2O.sub.5, ZrO.sub.2, CaO, MgO, HfO.sub.2, CaTiO.sub.3 and MgTiO.sub.3, and suitable for forming an apatite phase upon reaction with these by-products. For example, an oxide of the general formula A.sub.4B.sub.2O.sub.11-δ (A being selected from Y, La and Lu, and B being selected from Ta and Nb) is suitable for forming a secondary oxide of the general formula A.sub.6B.sub.4O.sub.19. The atomic fraction of reactive cation (i.e., of compound A) in the secondary oxide is substantially equal to 20.69%.

[0064] The elements A′ and A″ may be the same element A: the oxide of the reactive layer 9 may be described by the formula A.sub.4 B′.sub.2-yB″.sub.yO.sub.11-δ. The elements of the oxide are selected from the elements described in Table 2.

TABLE-US-00002 TABLE 2 A B′ B″ Sc, Y, La, Ta, Nb Ta, Nb, Ce, Pr, Ti, Zr, Nd, Pm, Hf, Al, Ce Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu

[0065] Thus, the atomic fraction of rare earth and/or yttrium and/or scandium and/or aluminum can be increased compared with known oxides, due to the structure of the oxide.

[0066] The elements B′ and B″ may also be the same element B, selected from Ta and Nb. In this case, the general formula of the oxide is A′.sub.4-xA″.sub.xB.sub.2O.sub.11-δ.

[0067] Advantageously, and in order to simplify the manufacture of the reactive layer 9, the same elements can be selected on the one hand for A′ and A″ and on the other hand for B′ and B″. In this case, the oxide can be described by the formula A.sub.4B.sub.2O.sub.11.

[0068] The reactive layer 9 may also comprise at least one complementary oxide selected from yttriated zirconia, Al.sub.2O.sub.3, Y.sub.2O.sub.3—ZrO.sub.2—Ta.sub.2O.sub.5 and an oxide of formula C.sub.2D.sub.2O.sub.7, wherein C is selected from a rare earth and yttrium and D is selected from zirconia and silicon. The one or more complementary oxides are known to exhibit properties to increase the life of parts exposed to CMAS compounds. The complementary oxide(s) exhibit properties different from the oxide, such as the reaction kinetics with the CMAS compound and/or the reaction products with the CMAS compound. The properties of the oxide and the complementary oxide can thus be combined in the reactive layer 9.

[0069] The reactive layer 9 may also have an average volume fraction of oxide that varies with increasing distance from the substrate 2. Thus, the reactive layer 9 has a gradient of volume fraction of oxide. A reactive layer 9 having an oxide gradient may for example be manufactured by depositing a succession of reactive sublayers, each sublayer having a different volume fraction of oxide.

[0070] Another aspect of the invention is a process for protecting a part from molten sand(s). The process comprises a step of depositing the reactive layer 9 as described above, on a part 1. After deposition, the part 1 comprises the reactive layer 9. The reactive layer 9 may be deposited directly on the substrate 2 of the part 1, for example a superalloy substrate 2, or on one or more layers of an environmental barrier 3. The deposition of the reactive layer 9 may be performed on at least one of the layers forming the environmental barrier 3, and preferentially on the thermally insulating layer 7. Thus, and unlike known parts, the part 1 comprising the reactive layer 9 deposited on the thermally insulating layer 7 has sufficient reactivity with the CMAS compound(s) 8 to produce at least one apatite phase before the insertion of the molten CMAS compound(s) 8 into the interstices of the thermally insulating layer 7, and thus avoid or limit this insertion. In this way, it is more difficult for the CMAS compound(s) 8 to access the surface of the environmental barrier 3, and their effect on the breakdown of the environmental barrier 3 is limited.

EXAMPLES

Example 1: Reaction Between a Liquid CMAS and a Reactive Layer of Gd.SUB.4.Nb.SUB.1.5.Zr.SUB.0.5.O.SUB.10.75

[0071] With reference to FIG. 8, a reactive layer 9 comprising the oxide Gd.sub.4Nb.sub.1.5Zr.sub.0.5O.sub.10.75 is subjected to chemical attack by a molten CMAS 8. The reactive layer 9 is deposited by spark plasma sintering (SPS).

[0072] With reference to FIG. 9, after a reaction time for example greater than 5 min, preferentially greater than 1 minute, a part of the reactive layer 9 is dissolved by the CMAS compound 8, and an apatite phase Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2 impervious to the molten CMAS 8 is formed between the reactive layer 9 and the molten CMAS 8. The Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2 layer is also impermeable to other reaction products (by-products) between the reactive layer 9 and the CMAS compounds 8. The Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2 layer is also able to produce secondary phases, allowing the reactive layer 9 to be protected. The environmental barrier 3 does not have any cracks. Indeed, the reservoir of compound cations A, i.e., A′ and A″ when A′ and A″ are the same element, makes it possible to form a tight layer and thus to limit the penetration depth, compared with the use of a known reactive layer such as La.sub.2Zr.sub.2O.sub.7.

Example 2: Reaction Between a Liquid CMAS and a Reactive Layer of Y.SUB.2.Gd.SUB.2.Ta.SUB.2.O.SUB.11

[0073] With reference to FIG. 8, a reactive layer 9 comprising the oxide Y.sub.2Gd.sub.2Ta.sub.2O.sub.11 is subjected to chemical attack by a molten CMAS 8. The reactive layer 9 is deposited by suspension plasma spraying (SPS).

[0074] With reference to FIG. 8b, after a reaction time for example greater than 5 min, preferentially greater than 1 minute, part of the reactive layer 9 is dissolved by the CMAS compound 8, and two apatite phases Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2 and Ca.sub.2Y.sub.6(SiO.sub.4).sub.6O.sub.2 impervious to the molten CMAS 8 are formed between the reactive layer 9 and the molten CMAS 8. The environmental barrier 3 has no cracks. Indeed, the reservoir of Y and Gd cations makes it possible to form two tight layers in large quantity and thus to limit the penetration depth, compared with the use of a known reactive layer such as La.sub.2Zr.sub.2O.sub.7. Indeed, six Y.sup.3+ cations are sufficient to preferentially form the apatite Ca.sub.4Y.sub.6(SiO.sub.4).sub.6O whereas eight Gd.sup.3− cations are necessary to form the apatite of more complex crystallographic structure Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2. In addition, the formation of two different layers as a reaction product between the reactive layer 9 and the CMAS 8 increases the kinetics of this reaction.

Example 3: Reaction Between a Liquid CMAS and a Reactive Layer of Gd.SUB.3.1.Al.SUB.0.9.Ta.SUB.1.7.Ti.SUB.0.5.O.SUB.10.85

[0075] With reference to FIG. 9, a reactive layer 9 comprising the oxide Gd.sub.3.1Al.sub.0.9Ta.sub.1.7Ti.sub.0.5O.sub.10.85 is subjected to chemical attack by a molten CMAS 8. The reactive layer 9 is deposited by suspension plasma spraying (SPS).

[0076] With reference to FIG. 8b, after a reaction time for example greater than 5 min, preferentially greater than 1 min, a part of the reactive layer 9 is dissolved by the CMAS compound 8, and a phase 10 of apatite Ca.sub.2Gd.sub.8(SiO.sub.4).sub.6O.sub.2 impervious to the molten CMAS 8 is formed between the reactive layer 9 and the molten CMAS 8. In addition, an anorthite phase CaAl.sub.2Si.sub.2O.sub.8 was also produced. This phase is suspended in the molten CMAS 8. The environmental barrier 3 does not show any cracks. Indeed, the cation reservoir allows to form two tight layers in large quantity and thus to limit the penetration depth, compared with the use of a known reactive layer such as La.sub.2Zr.sub.2O.sub.7. The modification of the mobility of the CMAS 8 by producing the anorthite secondary phase and the apatite phase thus limits the possibility for the liquid to penetrate the still healthy Gd.sub.3.1Al.sub.0.9Ta.sub.1.7Ti.sub.0.5O.sub.10.85 layer.