Turbine part made of superalloy comprising rhenium and/or ruthenium and associated manufacturing method

Abstract

A turbine part, such as a turbine blade or a distributor fin, for example, including a substrate made of superalloy based on monocrystalline nickel, including rhenium and/or ruthenium, and having a γ′-NisAI phase that is predominant by volume and a γ-Ni phase, the part also including a sublayer made of metal superalloy based on nickel covering the substrate, wherein the sublayer has a γ′-NisAI phase that is predominant by volume and wherein the sublayer has an average atomic fraction of aluminium of between 0.15 and 0.25, of chromium of between 0.03 and 0.08, of platinum of between 0.01 and 0.05, of hafnium of less than 0.01 and of silicon of less than 0.01. A process for manufacturing a turbine part including a step of vacuum deposition of a sublayer made of a superalloy based on nickel having predominantly by volume a γ′-NisAI phase, on a substrate made of superalloy based on nickel including rhenium and/or ruthenium.

Claims

1. A turbine part comprising: a substrate made of a single-crystal nickel-base superalloy, comprising at least one of rhenium or ruthenium, and having a γ′-Ni.sub.3Al phase which is predominant in volume and a γ-Ni phase, and a bond coat made of a nickel-based metal superalloy covering the substrate, wherein the bond coat has a γ′-Ni.sub.3Al phase of majority volume, wherein the bond coat has an average atomic fraction: of aluminum between 0.15 and 0.25; of chromium between 0.03 and 0.08; of platinum between 0.01 and 0.05; of hafnium less than 0.01 and of silicon less than 0.01, and wherein the part comprises a protective layer of aluminum oxide covering the bond coat.

2. The part as claimed in claim 1, wherein the bond coat has the γ′-Ni.sub.3Al phase greater than 95% by volume.

3. The part as claimed in claim 1, wherein the bond coat has the γ′-Ni.sub.3Al phase and a β-NiAlPt phase.

4. The part as claimed in claim 1, wherein the bond coat has the γ′-Ni.sub.3Al phase and a γ-Ni phase.

5. The part as claimed in claim 1, wherein the rhenium mass fraction of the substrate is greater than or equal to 0.04.

6. The part as claimed in claim 1, wherein the bond coat further comprises at least one element selected from cobalt, molybdenum, tungsten, titanium, and tantalum.

7. The part as claimed in claim 1, further comprising a thermally insulating ceramic layer covering the protective layer.

8. The part as claimed in claim 1, wherein a thickness of the bond coat is between 5 μm and 50 μm.

9. A turbine blade comprising: a turbine part comprising a substrate made of a single-crystal nickel-base superalloy, comprising at least one of rhenium or ruthenium, and having a γ′-Ni.sub.3Al phase which is predominant in volume and a γ-Ni phase, and a bond coat made of a nickel-based metal superalloy covering the substrate, wherein the bond coat has a γ′-Ni.sub.3Al phase of majority volume, wherein the bond coat has an average atomic fraction: of aluminum between 0.15 and 0.25; of chromium between 0.03 and 0.08; of platinum between 0.01 and 0.05; of hafnium less than 0.01 and of silicon less than 0.01, and wherein the part comprises a protective layer of aluminum oxide covering the bond coat.

10. A gas turbine engine comprising a turbine comprising the turbine blade as claimed in claim 9.

11. A process for manufacturing a turbine part comprising: a step of vacuum deposition of a bond coat of a nickel-based superalloy having a γ′-Ni.sub.3Al phase predominantly in volume, on a substrate made of a nickel-based superalloy comprising at least one of rhenium or ruthenium, the bond coat having an average atomic fraction: of aluminum between 0.15 and 0.25; of chromium between 0.03 and 0.08; of platinum between 0.01 and 0.05; of hafnium less than 0.01 and of silicon less than 0.01; and a step of formation of a protective layer of aluminum oxide covering the bond coat.

12. The process as claimed in claim 11, wherein the deposition is carried out by a method selected from physical vapor deposition, thermal spraying, Joule evaporation, pulsed laser ablation and sputtering.

13. The process as claimed in claim 11, wherein the bond coat is deposited by at least one of co-spraying or co-evaporating metal targets.

Description

PRESENTATION OF THE DRAWINGS

(1) Other features and advantages will be further highlighted in the following description, which is purely illustrative and non-limiting, and should be read in conjunction with the appended figures, among which:

(2) FIG. 1 shows a schematic diagram of the cross-section of a turbine part, for example a turbine blade or a nozzle vane;

(3) FIG. 2 is a microphotograph of the section of a bond coat covering the substrate;

(4) FIG. 3 is a microphotograph of the section of a bond coat covering the substrate;

(5) FIG. 4 schematically illustrates the section of a thermal barrier covering the substrate of a turbine part according to an embodiment of the invention;

(6) FIG. 5 is a microphotograph of the section of a bond coat covering a substrate after heat treatment;

(7) FIG. 6 is a microphotograph of the section of a bond coat covering the substrate after heat treatment.

DEFINITIONS

(8) The term “superalloy” refers to a complex alloy with very good resistance to oxidation, corrosion, creep and cyclic (especially mechanical or thermal) stress at high temperature and pressure. Superalloys have a particular application in the manufacture of parts used in aeronautics, for example turbine or gas turbine engine blades, as 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).

(9) A superalloy may have a two-phase microstructure comprising a first phase (called “γ phase”) forming a matrix, and a second phase (called “γ′ phase”) forming precipitates hardening in the matrix.

(10) The “base” of the superalloy is the main metal component of the matrix. In the majority of cases, superalloys include an iron, cobalt, or nickel base, but sometimes also a titanium or aluminum base.

(11) “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.

(12) Nickel-base superalloys consist of a γ phase (or matrix) of the face-centered austenitic cubic γ-Ni type, optionally containing additives in solid solution of α substitution (Co, Cr, W, Mo), and a γ′ phase (or precipitates) of type γ′-Ni.sub.3X, with X═Al, Ti or Ta. The γ′ phase has an ordered L.sub.12 structure, derived from the face-centered cubic structure, coherent with the matrix, i.e. having an atomic lattice very close thereto.

(13) Due to its orderly character, the γ′ phase has the remarkable property of having a mechanical resistance that increases with temperature up to about 800′C. The coherence between the γ and γ′ phases confers a very high hot mechanical strength of nickel-based superalloys, which itself depends on the ratio γ/γ′ and the size of the hardening precipitates.

(14) A superalloy is, in all the embodiments of the invention, rich in rhenium and/or ruthenium i.e. the average atomic fraction of rhenium and/or ruthenium in the superalloy is greater than or equal to 0.04. The presence of rhenium increases the creep resistance of the superalloy parts compared to the rhenium-free superalloy parts without ruthenium. In addition, the presence of ruthenium improves the distribution of refractory chemical elements in the γ and γ′ phases.

(15) Nickel-based superalloys thus generally have a high mechanical strength up to 700° C., then a mechanical strength that decreases sharply above 800° C.

(16) The term “atomic fraction” refers to the concentration.

DETAILED DESCRIPTION OF THE INVENTION

(17) FIG. 4 schematically illustrates a section of thermal barrier 10 covering the substrate 2 of a turbine part 1.

(18) The components shown in FIG. 4 may be independently representative of the components of a turbine blade 6, a nozzle vane, or any other component, part or piece of a turbine.

(19) The substrate 2 is formed from a nickel-based superalloy comprising rhenium and/or ruthenium. The average mass fraction of the rhenium and/or ruthenium substrate 2 is greater than or equal to 0.04 and preferentially between 0.045 and 0.055.

(20) The thermal barrier consists of a metal bond coat 3b, a protective layer 4 and a thermal insulating layer 9.

(21) The substrate 2 is covered by the metallic bond coat 3b. The metal layer 3b is covered by the protective layer 4. The protective layer 4 is covered by the thermally insulating layer 9.

(22) The composition of the deposited metallic bond coat 3b has an average atomic fraction of aluminum between 0.15 and 0.25, preferentially between 0.19 and 0.23, of chromium between 0.03 and 0.08, preferentially between 0.03 and 0.06, of platinum between 0.01 and 0.05, of hafnium less than 0.01, preferentially less than 0.008, and of silicon less than 0.01, preferentially less than 0.008. The preferential composition is described in Table 1 below, the average atomic fraction being given in percent.

(23) TABLE-US-00001 TABLE 1 Ni (% At) Al (% At) Cr (% At) Pt (% At) Hf (% At) If (% At) base 19-23 3-6 1-5 0-0.8 0-0.8

(24) The metallic bond coat 3b has a γ′-Ni.sub.3Al phase 12 majority by volume. Thus, the allotropic structure of the bond coat 3b is close to the structure of the substrate 2, preventing the formation of secondary reaction zones during the use of the turbine part 1 at temperatures above 900° C., and preferentially above 1100′C. Advantageously, the γ′-Ni.sub.3Al phase is greater than 95% by volume in the metal bond coat. Apart from the γ′-Ni.sub.3Al phase, the metal bond coat 3b may have a ß-NiAlPt phase or a γ-Ni phase.

(25) The chemical composition and the allotropic structure of the bond coat 3b were determined by analyzing the chemical composition and structure of a bond coat 3b, initially of type ß-NiAlPt, directly after a martensitic transformation phase during a treatment of the bond coat 3b simulating the thermal conditions of use of the part 1.

(26) FIG. 5 is a microphotograph of the section of a bond coat 3a, different from a bond coat of the invention, covering a substrate after heat treatment. The substrate covered by the bond coat 3a is a substrate made of a nickel-based superalloy of the AM1 type, comprising neither rhenium nor ruthenium. The part comprising the bond coat 3a has been treated by a series of 250 thermal cycles, each cycle corresponding to a thermal treatment of the part comprising the bond coat 3a at a temperature of 1100° C. for 60 minutes. The majority of the volume of the bond coat 3a is a ß-NiAlPt phase 11 and the minority is a γ′-Ni.sub.3Al phase 12. The bond coat 3a is covered by a protective layer 4. The interface between the bond coat 3a and the protective layer 4 is very irregular: it has a roughness high enough to cause the protective layer 4 to flake (or rumple) when the part is used. This roughness is caused during heat treatment by martensitic transformations of the ß-NiAlPt phases 11 in the bond coat 3a.

(27) FIG. 6 is a microphotograph of the section of a bond coat 3b, in accordance with an embodiment of the invention, covering a substrate 2 made of a single-crystal nickel-based superalloy comprising rhenium and/or ruthenium, after a heat treatment. The part comprising the bond coat 3b has been treated by a series of 500 thermal cycles, each cycle corresponding to a heat treatment of the part 1 comprising the bond coat 3b at a temperature of 1100° C. for 60 minutes. The majority of the volume of the bond coat 3b is a γ′-Ni.sub.3Al phase 12 and the minority is a ß-NiAlPt phase 11. The bond coat 3a is covered by a protective layer 4. The interface between the bond coat 3b and the protective layer 4 has a lower roughness than the roughness between the bond coat 3a and the protective layer 4 shown in FIG. 5, despite a heat treatment of the system comprising the bond coat 3b that is longer than the heat treatment described with reference to FIG. 5. This difference in roughness is associated with a faster martensitic transformation of the ß-NiAlPt phases 11 of the bond coat 3b than that of the ß-NiAlPt phases 11 of the bond coat 3a. In addition, the bond coat 3b illustrated in FIG. 6 presents mainly by volume a γ′-Ni.sub.3Al phase 12 and less by volume a ß-NiAlPt phase 11.

(28) The allotropic structure and the chemical composition of the bond coat 3b after 500 thermal cycles were analyzed and selected. This structure and composition correspond to the structure and compositions described above, particularly in Table 1.

(29) Thus, due to a γ′-Ni.sub.3Al phase 12 majority in volume and due to the composition described in Table 1, the bond coat 3b is subject little if at all to the martensitic transformations leading to the rumpling phenomenon, while presenting a composition that increases the time, under working conditions, during which the protective bond coat 4 can be formed.

(30) The bond coat 3b can be deposited under vacuum, for example by means of physical vapor deposition (PVD). Different PVD methods can be used for the manufacture of the bond coat 3b, such as sputtering, Joule evaporation, laser ablation and electron beam assisted physical vapor deposition. The bond coat 3b can also be deposited by thermal spraying.

(31) Thus, the bond coat 3b can be deposited on the substrate 2 by presenting, before any heat treatment, a chemical composition and an allotropic structure adapted to avoid the rumpling phenomenon.

(32) These deposition methods also simplify the formation of the bond coat 3b on the substrate 2 as well as better control of the chemical composition of the bond coat 3b.

(33) Finally, these deposition methods allow precise control of the thickness of the bond coat 3b, unlike the methods of metal bond coat formation by chemical element diffusion. Advantageously, the thickness of the bond coat 3b is between 5 μm and 50 μm.

(34) Several targets of different metallic materials can be used in parallel, simultaneously, when depositing a bond coat 3b. This type of deposition can be carried out by co-evaporation or by co-sputtering: the rate, respectively of evaporation or sputtering imposed on each target during the deposition of the bond coat 3b then determines the stoichiometry of said layer.