TURBINE PART MADE OF SUPERALLOY COMPRISING RHENIUM AND/OR RUTHENIUM AND ASSOCIATED MANUFACTURING METHOD

Abstract

The present invention concerns a turbine part comprising a substrate made of nickel-based monocrystalline superalloy, comprising chromium and at least one element chosen among rhenium and ruthenium, the substrate having a γ-γ′ phase, an average mass fraction of rhenium and of ruthenium greater than or equal to 4% and an average mass fraction of chromium less than or equal to 5% and preferably less than or equal to 3%, a sub-layer covering at least a part of a surface of the substrate, characterised in that the sublayer has a γ-γ′ phase and an average atomic fraction of chromium greater than 5%, of aluminium between 10% and 20% and of platinum between 15% and 25%.

Claims

1. A turbine part, comprising a single-crystal nickel-base superalloy substrate and a sublayer, the single-crystal nickel-base superalloy substrate, comprising chromium and at least one element selected from rhenium and ruthenium, and having a γ-γ′ phase, an average mass fraction of rhenium and ruthenium greater than or equal to 4% and an average mass fraction of chromium less than or equal to 5%, the sublayer covering at least part of a surface of the substrate, wherein the sublayer has a γ-γ′ phase and an average atomic fraction: of chromium comprised between 5% and 10%, of aluminum comprised between 10% and 20%, and of platinum comprised between 15% and 25%.

2. The turbine part as claimed in claim 1, wherein the sublayer has exclusively a γ-γ′ phase.

3. The turbine part as claimed in claim 1, wherein the sublayer has an average atomic fraction of silicon less than 2%.

4. The turbine part as claimed in claim 1, wherein the sublayer has a thickness comprised between 5 μm and 50 μm.

5. The turbine part as claimed in claim 1, comprising a protective layer of aluminum oxide covering the sublayer.

6. The turbine part as claimed in claim 5, comprising a ceramic thermal insulation layer covering the protective layer of aluminum oxide.

7. A turbine blade, comprising the turbine part as claimed in claim 1.

8. A process for manufacturing a turbine part, comprising a single-crystal nickel-base superalloy substrate and a sublayer, the single-crystal nickel-base superalloy substrate, comprising chromium and at least one element selected from rhenium and ruthenium, having a γ-γ′ phase, an average mass fraction of rhenium and ruthenium greater than or equal to 4% and an average mass fraction of chromium less than or equal to 5%, the sublayer covering at least part of a surface of the substrate, the sublayer having a γ-γ′ phase and an average atomic fraction: of chromium comprised between 5% and 10%, of aluminum comprised between 10% and 20%, of platinum comprised between 15% and 25%, wherein the process comprises at least the steps of: a) depositing an enrichment layer on the substrate, the enrichment layer having at least an average atomic fraction of platinum greater 90% and an average atomic fraction of chromium comprised between 3% and 10%, b) heat treating the assembly formed by the substrate and the enrichment layer so that the enrichment layer diffuses at least partially into the substrate.

9. The process as claimed in claim 8, wherein, during step a) of depositing an enrichment layer, at least one chromium layer and one platinum layer are deposited separately, the chromium layer or layers having a total thickness comprised between 200 nm and 2 μm and the platinum layer or layers having a total thickness comprised between 3 μm and 10 μm.

10. The process as claimed in claim 8, wherein, during step a) of depositing an enrichment layer, chromium and platinum are deposited simultaneously.

11. The process as claimed in claim 8, wherein the assembly formed by the substrate and the enrichment layer is heat treated at a temperature above 1000° C. for more than one hour.

12. The process as claimed in claim 8, wherein the deposition of the enrichment layer is carried out by a method selected from physical vapor deposition, thermal spraying, electron beam evaporation, pulsed laser ablation and cathode sputtering.

13. The turbine part as claimed in claim 1, wherein the single-crystal nickel-base superalloy substrate has an average mass fraction of chromium less than or equal to 3%.

14. The turbine part as claimed in claim 1, wherein the sublayer has a thickness comprised between 5 μm and 15 μm.

15. The process as claimed in claim 8, wherein the single-crystal nickel-base superalloy substrate has an average mass fraction of chromium less than or equal to 3%.

16. The process as claimed in claim 8, wherein the assembly formed by the substrate and the enrichment layer is heat treated at a temperature above 1000° C. for more than 2 hours.

17. The turbine part as claimed in claim 2, wherein the sublayer has an average atomic fraction of silicon less than 2%.

18. The turbine part as claimed in claim 2, wherein the sublayer has a thickness comprised between 5 μm and 50 μm.

19. The turbine part as claimed in claim 2, comprising a protective layer of aluminum oxide covering the sublayer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0061] FIG. 4 illustrates a process for manufacturing a part 1, comprising a substrate 2 and a sublayer 4. The substrate 2 used is of the type CMSX-4 plus (registered trademark) and has the chemical composition, in average atomic fraction, described in Table 1.

TABLE-US-00001 TABLE 1 Cr Co Mo Ta W Cb Re Al Ti Hf Ni 3.5 10 0.6 8 6 0 4.8 5.7 0.85 0.1 Balance

[0062] In a first step 401 of the process, an enrichment layer 11 is deposited on the substrate 2. The enrichment layer 11 has at least an average atomic fraction of platinum greater than 90% and an average atomic fraction of chromium comprised between 3% and 10%. The enrichment layer 11 comprises at least chromium and platinum, and preferentially chromium, platinum, hafnium and silicon. Preferentially, the enrichment layer 11 does not include nickel. The individual elements of the enrichment layer 11 may be alloyed.

[0063] The different elements of the enrichment layer 11 may be deposited simultaneously. The enrichment layer 11 may also comprise several superimposed layers: each element may be deposited separately. In particular, at least one layer of platinum and at least one layer of chromium can be deposited separately. In this case, the chromium layer or layers have a total thickness comprised between 200 nm and 2 μm and the platinum layer or layers have a total thickness comprised between 3 μm and 10 μm. Thus, the quantity of metals diffused during the process in accordance with an embodiment of the invention is optimized.

[0064] The deposition of the layer or layers forming the enrichment layer 11 can be carried out under vacuum, for example by a physical vapor deposition (PVD) process. Various PVD methods can be used to produce the enrichment layer 11, such as cathode sputtering, electron beam evaporation, laser ablation and electron-beam physical vapor deposition. The enrichment layer 11 may also be deposited by thermal spraying.

[0065] In a second step 402 of the process, the assembly formed by the substrate 2 and the enrichment layer 11 is thermally treated so that the enrichment layer 11 diffuses at least partially into the substrate 2. Thus, a sublayer 4 is formed on the surface of the substrate 2. The heat treatment is preferentially carried out for more than one hour at a temperature comprised between 1000° C. and 1200° C., preferentially for more than two hours at a temperature comprised between 1000° C. and 1200° C., and even more preferentially substantially four hours at a temperature comprised between 1050° C. and 1150° C.

[0066] In general, a sufficient quantity of platinum and chromium is deposited during step 401 so that, after heat treatment step 402, the average atomic fraction of platinum in the sublayer 4 is comprised between 15% and 25%, and so that the average atomic fraction of chromium in the sublayer 4 is greater than 5% and preferentially comprised between 5% and 20%. The quantity of platinum and chromium deposited in the enrichment layer 11 is therefore all the higher as the chromium and platinum atomic mole fraction of the substrate 2 is lower, which is typically the case for a substrate 2 enriched in rhenium and/or ruthenium.

[0067] The thickness of the enrichment layer 11 is preferentially comprised between 100 nm and 20 μm.

[0068] FIG. 5 is a scanning electron microscopy photograph of the microstructure of a substrate 2 and a sublayer 4 of a part 1. The sublayer 4 is produced by the process shown in FIG. 4, in which an enrichment layer 11 comprising only chromium and platinum is deposited during step 401 of the process. The scale bar in FIG. 5 corresponds to a length equal to 20 μm. The sublayer 4 has, in general, a γ-γ′ phase and an average atomic fraction of chromium greater than 5%, preferentially comprised between 5% and 20%, of aluminum comprised between 10% and 20%, of platinum comprised between 15% and 25%. In particular, the sublayer 4 has an average atomic fraction of chromium substantially equal to 5.8%, an average atomic fraction of aluminum substantially equal to 11%, an average atomic fraction of platinum substantially equal to 21%, an average atomic fraction of hafnium less than 0.5% and an average atomic fraction of silicon less than 1%.

[0069] The sublayer 4 preferentially has exclusively a γ-γ′ phase. Indeed, the introduction of elements into the substrate 2 by the enrichment process described above make it possible not to cause a phase transition of the substrate 2, and thus to avoid mechanical stresses in the substrate 2 that could lead to the appearance of cracks 8. A substantially horizontal line divides the sublayer 4 into two superimposed parts: this line corresponds to the boundary between the substrate 2 and the enrichment layer 11, prior to the heat treatment step 402 during the manufacture of a part 1.

[0070] The thickness of the sublayer 4 is typically comprised between 1 μm and 100 μm, and preferentially between 5 μm and 50 μm.

[0071] In particular, the average atomic fraction of chromium in the sublayer 4 helps to promote the formation of α-Al.sub.2O.sub.3 when the part is used in working conditions.

[0072] With reference to FIG. 6, the sublayer 4 helps prevent cracking during extended heat treatment, representative of working conditions in a turbine. The scale bar corresponds to a length equal to 20 μm. FIG. 6 is a scanning electron microscopy photograph of a part 1 comprising the substrate 2 and the sublayer 4, after the extended heat treatment. During the extended heat treatment, the part 1 is placed under air for 100 hours at 1050° C. and then for 10 hours at 1150° C. No cracks 8 are detectable in the substrate 2 after the extended heat treatment.