RU2777682C2 - Turbine part of superalloy with rhenium and/or ruthenium content and its manufacturing method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to a turbine part, such as a turbine blade or, for example, a nozzle device blade, containing substrate made of a monocrystal superalloy based on nickel, containing rhenium and/or ruthenium, as well as γ’-Ni₃Al phase prevailing in volume, and γ-Ni phase, while the part also contains a sublayer of a metal superalloy based on nickel, covering substrate. According to the invention, the sublayer contains γ’-Ni₃Al phase prevailing in volume, while the sublayer contains an average atomic fraction of aluminum in the amount from 0.15 to 0.25, chromium in the amount from 0.03 to 0.08, platinum in the amount from 0.01 to 0.05, hafnium in the amount of less than 0.01, and silicon in the amount of less than 0.01. A method for the manufacture of a turbine part includes a stage of vacuum application of the sublayer of the superalloy based on nickel, containing γ’-Ni₃Al phase prevailing in volume, to substrate of the superalloy based on nickel with a rhenium and/or ruthenium content, while the sublayer contains an average atomic fraction of aluminum in the amount from 0.15 to 0.25, chromium in the amount from 0.03 to 0.08, platinum in the amount from 0.01 to 0.05, hafnium in the amount of less than 0.01, and silicon in the amount of less than 0.01.

EFFECT: protection from oxidation and corrosion of a turbine part of superalloy, and increase in its service life during the operation compared to known parts, as well as prevention or limitation of the formation of secondary reaction zones in substrate and exfoliation of a protective layer of aluminum oxide.

13 cl, 6 dwg

Description

The technical field to which the invention belongs

The invention relates to a turbine component, such as a turbine blade or a nozzle blade, used in the aircraft industry.

State of the art

In a turbojet engine, the combustion gases leaving the combustion chamber can reach high temperatures in excess of 1200°C, even 1600°C. Parts of a turbojet engine that come into contact with these combustion gases, such as turbine blades, must therefore be able to maintain their mechanical properties at these high temperatures.

To do this, as you know, some parts of the turbojet engine are made of "superalloy". Nickel-based superalloys generally form a group of high tensile metal alloys capable of operating at temperatures relatively close to their melting point (typically a factor of 0.7 to 0.8 of their melting point).

To improve the thermal stability of such superalloys and protect them from oxidation and corrosion, it is customary to apply a coating on them, which plays the role of a thermal barrier.

In FIG. 1 shows a schematic cross-section of a turbine part 1, for example a turbine blade 6 or a nozzle blade. Part 1 contains a substrate 2 of a single-crystal metal superalloy coated with a thermal barrier 10.

The thermal barrier typically comprises a metal sublayer, a protective layer, and a heat insulating layer. The metal sublayer covers the metal superalloy substrate. The metal sublayer itself is covered with a protective layer formed as a result of the oxidation of the metal sublayer. The protective layer protects the superalloy substrate from corrosion and/or oxidation. The heat-insulating layer covers the protective layer. The thermally insulating layer may be ceramic, for example, from yttrium-containing zirconia.

The underlayer may be plain nickel aluminide β-NiAl or platinum-modified nickel aluminide β-NiAlPt. The average aluminide atomic fraction (0.35 - 0.45) of the sublayer is sufficient to completely form a protective layer of aluminum oxide (Al ₂ O ₃ ) that protects the superalloy substrate from oxidation and corrosion.

However, when the workpiece is exposed to high temperatures, the difference in the concentrations of nickel and mainly aluminum in the superalloy substrate and the metal sublayer causes diffusion of different elements, in particular, the nickel contained in the substrate towards the metal sublayer, and also the aluminum contained in the metal sublayer towards the superalloy. This phenomenon is called "mutual diffusion".

Mutual diffusion can lead to the formation of primary and secondary reaction zones (SRZ = Secondary Reaction Zone) in that part of the substrate that is in contact with the sublayer.

In FIG. 2 shows a micrograph of a section of the sublayer 3a covering the substrate 2. The photomicrograph was taken before the part was subjected to a series of heat treatment cycles to simulate the temperature conditions that part 1 experiences during its operation. The substrate 2 is rich in rhenium, i.e. the average mass fraction of rhenium is greater than or equal to 0.04. Rhenium is known to be used in superalloys to increase the creep resistance of superalloy parts. Typically, the substrate 2 contains a γ-Ni phase. Sublayer 3a is of the β-NiAlPt type. The substrate contains a primary interdiffusion zone 5 located in that part of the substrate which is directly covered by the sublayer 3a. The substrate 2 also contains a secondary interdiffusion zone 6 which is directly covered by a primary interdiffusion zone 5 . The thickness of the secondary, shown in Fig. 2 zone 6 mutual diffusion is essentially 35 microns.

In FIG. 3 shows a micrograph of a cross-section of sublayer 3a covering substrate 2. The micrograph shows sublayer 3a and substrate 2 after they have been subjected to the series of heat treatment cycles described above. The sublayer 3a covers the substrate 2. The substrate 2 comprises a primary interdiffusion zone 5 and a secondary interdiffusion zone 6. Locally, the thickness of the secondary interdiffusion zone 6 can reach 150 µm, as shown in FIG. 3 with a white segment.

Interdiffusion phenomena entail a premature depletion of the sublayer in aluminum, which promotes phase transformations in the sublayer (β-NiAl → γ'-Ni ₃ Al: martensitic transformation). Such transformations change the allotropic modification of the sublayer 3a and cause the formation of cracks 8 in it, which contribute to the peeling (rumpling) of the protective layer of aluminum oxide.

Thus, interdiffusion phenomena between the superalloy substrate and the underlayer can have negative consequences for the durability of the superalloy part.

Implementation of the invention

One of the technical objectives of the invention is to provide a solution for effective protection against oxidation and corrosion of a superalloy turbine part and increase its service life during operation compared to known parts.

Another technical challenge is to develop a solution to prevent or limit the formation of secondary reaction zones in the substrate and peeling of the protective layer of aluminum oxide.

The above technical problem is solved in a turbine part containing a substrate made of a nickel-based single-crystal superalloy containing rhenium and/or ruthenium, and having a γ'-Ni ₃ Al phase, which is predominant in the volume, as well as a γ-Ni phase, and covering sublayer of a nickel-based metal superalloy, wherein, according to the invention, the sublayer contains the γ'-Ni ₃ Al phase in the predominant volume, and the sublayer has an average atomic fraction of aluminum, which is from 0.15 to 0.25, chromium from 0, 03 to 0.08, platinum from 0.01 to 0.05, hafnium less than 0.01 and silicon less than 0.01.

Since the metal sublayer has an allotropic modification close to that of the substrate, an obstacle and/or limitation is created for the formation of secondary reaction zones.

In addition, since the composition of the metal sublayer corresponds to the composition of the sublayer under operating conditions at the time point following the martensitic transformation, the allotropic modification of the sublayer limits or prevents the formation of secondary reaction zones, maintaining a chemical composition that provides an increase in the time under operating conditions during which protective underlayer.

A turbine part may also have the following features:

- the sublayer contains the γ'-Ni ₃ Al phase in an amount of more than 95% by volume.

- the sublayer contains the γ'-Ni ₃ Al phase and the ß-NiAlPt phase,

the sublayer contains a γ'-Ni ₃ Al phase and a γ-Ni phase,

- the mass fraction of rhenium in the substrate is greater than or equal to 0.04,

- additionally, the sublayer contains at least one element selected from cobalt, molybdenum, tungsten, titanium and tantalum,

- a protective layer of aluminum oxide covers the sublayer,

- a ceramic heat-insulating layer covers the protective layer,

- the thickness of the sublayer is from 5 to 50 microns.

The invention also relates to a turbine blade containing the part described above.

The invention also relates to a gas turbine engine comprising a turbine equipped with a turbine blade as described above.

The invention also relates to a method for manufacturing a turbine part, which includes the step of applying in vacuum a sublayer of a nickel-based superalloy containing a γ'-Ni ₃ Al phase in a predominant volume onto a nickel-based superalloy substrate containing rhenium and/or ruthenium, with this sublayer contains the average atomic fraction:

- aluminum in an amount of 0.15 to 0.25,

- chromium in an amount of 0.03 to 0.08,

- platinum in an amount from 0.01 to 0.05,

- hafnium in an amount less than 0.01 and

- silicon in an amount less than 0.01.

The coating can be applied by a method selected from: physical vapor deposition, thermal deposition, Joule heat evaporation, laser pulsed ablation, and cathode deposition.

The sublayer can be deposited by simultaneous sputtering and/or simultaneous evaporation of metal targets.

Brief description of the drawings

Other features and advantages of the invention are given in the following description, which is purely illustrative, non-limiting and explained by the attached figures, in which:

in fig. 1 schematically shows a detail of a turbine, such as a turbine blade or a nozzle blade, in cross section;

in fig. 2 shows a micrograph of a substrate-covering sublayer, in sectional view;

in fig. 3 shows a micrograph of the sublayer covering the substrate, in sectional view;

in fig. 4 schematically shows a thermal barrier covering a substrate of a turbine part, according to an embodiment of the invention, in cross section;

in fig. 5 shows a micrograph of the sublayer covering the substrate after heat treatment, a cross-sectional view;

in fig. 6 shows a micrograph of the sublayer covering the substrate after heat treatment, a cross-sectional view.

Definition of concepts

The term "superalloy" refers to a complex alloy characterized at high temperature and high pressure by very good resistance to oxidation, corrosion, creep and cyclic stress (in particular mechanical or thermal). Superalloys are of particular use in the production of parts used in aircraft construction, such as turbine blades or gas turbine engines, as they form a group of alloys with high tensile strength, capable of operating at temperatures relatively close to their melting point (typically at a factor of 0.7 - 0, 8 from their melting point).

The superalloy may have a two-phase microstructure containing a first matrix-forming phase (referred to as the "γ phase") and a second phase (referred to as the "γ' phase"), which forms reinforcing particulate precipitates in the matrix.

The "base" of a superalloy means the main metal component of the matrix. In most cases, superalloys are based on iron, cobalt or nickel, but sometimes also titanium or aluminum.

"Nickel based superalloys" have the advantage of providing a good compromise between oxidation resistance, high temperature fracture resistance and weight, which makes them suitable for use in the hottest areas of turbojets.

Nickel-based superalloys are formed by the γ phase (or matrix) of the austenitic cubic face-centered type γ-Ni, containing, if necessary, additives in the form of a substituting solid solution α (Co, Cr, W, Mo), and the γ' phase (or precipitates) of the γ' type -Ni ₃ X, where: X is Al, Ti or Ta. The γ' phase has an ordered structure L ₁₂ derived from a cubic face-centered structure coherent with the matrix, i.e. containing an atomic lattice very close to the matrix.

According to its ordered nature, the γ' phase has the remarkable property that the mechanical strength increases with increasing temperature up to about 800ºС. The bonding between the γ and γ' phases gives nickel-based superalloys very high hot strength, which in turn depends on the γ/γ' ratio and on the size of the hardening particulate precipitates.

The superalloy, according to the totality of embodiments of the invention, is rich in rhenium and/or ruthenium, ie, the average atomic fraction of rhenium and/or ruthenium in the superalloy is greater than or equal to 0.04. The presence of rhenium makes it possible to increase the creep resistance of superalloy parts compared to superalloy parts without rhenium and ruthenium. In addition, the presence of ruthenium makes it possible to improve the distribution of high-temperature chemical elements in the γ and γ' phases.

Consequently, nickel-based superalloys have, as a rule, high mechanical strength at temperatures up to 700 ⁰ C, which decreases strongly at temperatures above 800 ⁰ C.

The term "atomic fraction" means concentration.

Implementation of the invention

In FIG. 4 schematically shows a section made along a thermal barrier 10 deposited on the substrate 2 of the turbine part 1.

The elements depicted in this figure may be completely typical elements of a turbine blade 6, a nozzle blade or any other element, part or part of a turbine.

The substrate 2 is made of a nickel-based superalloy containing rhenium and/or ruthenium. The average mass fraction of rhenium and/or ruthenium in the substrate 2 may be greater than or equal to 0.04, preferably between 0.045 and 0.055.

The thermal barrier comprises a metal sublayer 3b, a protective layer 4 and a heat insulating layer 9.

The substrate 2 is covered with a metal underlayer 3b. The metal underlayer 3b is covered with a protective layer 4. The protective layer 4 is covered with a heat-insulating layer 9.

The composition of the applied metal sublayer 3b contains an average atomic fraction of aluminum in an amount of from 0.15 to 0.25, preferably from 0.19 to 0.23, chromium in an amount of from 0.03 to 0.08, preferably from 0.03 to 0.06, platinum in an amount of 0.01 to 0.05, hafnium in an amount of less than 0.01, preferably less than 0.008, and silicon in an amount of less than 0.01, preferably less than 0.008. Table 1 below shows the preferred composition, with the average atomic fraction given as a percentage.

Table 1

Ni, at. % Al, at. % Cr, at. % Pt, at. % Hf, at. % Si, at. % The foundation 19 – 23 3 - 6 fifteen 0 - 0.8 0 - 0.8

The metal sublayer 3b contains the 12 γ'-Ni ₃ Al phase, which predominates in the volume. Therefore, the allotropic modification of the sublayer 3b is close to the modification of the substrate 2, which makes it possible to prevent the formation of secondary reaction zones during the use of turbine part 1 at temperatures above 900 ⁰ C, preferably above 1100 ⁰ C. Preferably, the γ'-Ni ₃ Al phase is contained in the metal sublayer in more than 95% by volume. In addition to the γ'-Ni ₃ Al phase, the metal sublayer 3b may also contain a β-NiAlPt phase or a γ-Ni phase.

The chemical composition and allotropic modification of sublayer 3b is determined by analyzing the chemical composition and modification of sublayer 3b, initially of the β-NiAlPt type, immediately after the martensitic transformation phase during processing of sublayer 3b while simulating the thermal conditions of use of part 1.

In FIG. 5 shows a micrograph of a section of a sublayer 3a, different from the sublayer according to the invention and covering the substrate after heat treatment. The substrate with sublayer 3a deposited on it is made of an AM1 type nickel-based superalloy without rhenium or ruthenium content. The part with sublayer 3a was subjected to a series of 250 heat treatment cycles, with each cycle corresponding to heat treatment of the part with sublayer 3a at a temperature of 1100 ⁰ C for 60 minutes. Underlayer 3a contained the 11 β-NiAlPt phase, which dominated in volume, and the 12 γ'-Ni ₃ Al phase, which was smaller in volume. The underlayer 3a was covered with the protective layer 4. The interface between the underlayer 3a and the protective layer 4 was very uneven: it had a rather pronounced bumpiness, causing the protective layer to peel off (rumping in English) when using the part. Such a lumpiness is formed during heat treatment due to martensitic transformations of the 11 β-NiAlPt phases in sublayer 3a.

In FIG. 6 is a micrograph of a cross-sectional view of an underlayer 3b according to an embodiment of the invention covering a substrate 2 of nickel-based single crystal superalloy containing rhenium and/or ruthenium after heat treatment. The part with sublayer 3b was processed in the form of a series of 500 heat treatment cycles, and each such cycle corresponded to the heat treatment of part 1 with sublayer 3b at a temperature of 1100 ⁰ C for 60 minutes. Underlayer 3b contained the 12 γ'-Ni ₃ Al phase, which dominated in volume, and the 11 β-NiAlPt phase, which was smaller in volume. The underlayer 3a was covered with the protective layer 4. The interface between the underlayer 3b and the protective layer 4 contained less pronounced roughness than the roughness between the underlayer 3a and the protective layer 4 in FIG. 5, despite the fact that the heat treatment of the system containing the sublayer 3b was longer than that described with reference to FIG. 5 heat treatment. This difference in lumpiness is explained by the martensitic transformation of the 11 β-NiAlPt phases of sublayer 3b, which occurred faster than the same transformation of the 11 β-NiAlPt phases in sublayer 3a. In addition, shown in Fig. 6, sublayer 3b contained the 12 γ'-Ni ₃ Al phase in a larger volume and the 11 β-NiAlPt phase in a smaller volume.

After 500 cycles of heat treatment, the allotropic modification and the chemical composition of the sublayer 3b were analyzed and selected. Such modification and composition correspond to the modification and compositions given above, in particular, in table 1.

Thus, due to the 12 γ'-Ni ₃ Al phase predominating in the volume and the composition shown in Table 1, sublayer 3b was little or not at all prone to martensitic transformations, causing a peeling effect, in the presence of a composition that increases the time for the formation of a protective sublayer of layer 4 in working conditions.

Underlayer 3b can be applied in a vacuum, for example, by physical vapor deposition (PVD = Physical Vapor Deposition). Various PVD physical vapor deposition methods can be used to deposit the underlayer 3b, such as cathode sputtering, Joule heat evaporation, laser irradiation ablation, and electron beam physical vapor deposition. Underlayer 3b can also be applied by thermal spraying.

In this way, the underlayer 3b can be applied to the substrate 2, which, prior to any heat treatment, has a chemical composition and allotropic modification that eliminates the peeling effect.

These coating methods also make it possible to simplify the formation of the sublayer 3b on the substrate 2 and to improve the control of its chemical composition.

Finally, these coating methods allow precise control of the thickness of the 3b sublayer, as opposed to the methods of forming a metal sublayer by diffusion of a chemical element. Preferably, the thickness of the underlayer 3b is between 5 and 50 µm.

When applying the underlayer 3b, several targets from different metallic materials can be used in parallel and simultaneously. This type of coating can be obtained by co-evaporation or co-sputtering: respectively, the rate of evaporation or sputtering when using each target during the deposition of the 3b sublayer determines the stoichiometry of this layer.

Claims (25)

1. Part (1) of the turbine, containing a substrate (2) made of a nickel-based single-crystal superalloy containing rhenium and/or ruthenium, and having a γ'-Ni ₃ Al phase in the predominant volume and a γ-Ni phase, and a sublayer ( 3b) from a metallic nickel-based superalloy, covering the substrate (2), characterized in that the sublayer (3b) has a phase (12) γ'-Ni ₃ Al, prevailing in volume, while the sublayer (3b) contains the average atomic fraction: - aluminum in an amount of 0.15 to 0.25, - chromium in an amount of 0.03 to 0.08, - platinum in an amount from 0.01 to 0.05, - hafnium in an amount less than 0.01 and - silicon in an amount less than 0.01, while the underlayer (3b) is covered with a protective layer (4) of aluminum oxide. 2. Part according to claim 1, in which the sublayer (3b) contains the phase (12) γ'-Ni ₃ Al in an amount of more than 95% by volume. 3. Part according to claim 1 or 2, in which the sublayer (3b) contains a phase (12) γ'-Ni ₃ Al and a phase (11) β-NiAlPt. 4. Part according to claim 1 or 2, wherein the sublayer (3b) contains a γ'-Ni ₃ Al phase (12) and a γ-Ni phase. 5. Detail according to any one of paragraphs. 1 - 4, in which the mass fraction of rhenium and/or ruthenium in the substrate (2) is greater than or equal to 0.04. 6. Detail according to any one of paragraphs. 1-4, in which the sublayer (3b) additionally contains at least one element selected from cobalt, molybdenum, tungsten, titanium and tantalum. 7. Detail according to any one of paragraphs. 1 - 6, containing a ceramic heat-insulating layer (9) covering the protective layer (4). 8. Detail according to any one of paragraphs. 1 - 7, in which the thickness of the sublayer (3b) is from 5 to 50 µm. 9. The blade (6) of the turbine, characterized in that it contains a part (1) according to any one of paragraphs. eighteen. 10. Gas turbine engine, characterized in that it contains a turbine containing a turbine blade (6) according to claim 9. 11. A method for manufacturing a part (1) of a turbine, including the step of vacuum deposition of a sublayer (3b) of a nickel-based superalloy containing a bulk-dominant γ'-Ni ₃ Al phase on a substrate (2) of a nickel-based superalloy containing rhenium and/or ruthenium, with the sublayer (3b) containing the average atomic fraction: - aluminum in an amount of 0.15 to 0.25, - chromium in an amount from 0.03 to 0.08, - platinum in an amount from 0.01 to 0.05, - hafnium in an amount of less than 0.01 and - silicon in an amount less than 0.01, and the step of forming a protective layer (4) of alumina covering the sublayer (3b). 12. The method of claim. 11, wherein the coating is performed by a method selected from the methods of physical vapor deposition, thermal spraying, evaporation by Joule heat, pulsed laser ablation and cathode sputtering. 13. The method according to claim 11 or 12, wherein the underlayer (3b) is deposited by co-sputtering and/or co-evaporation of metal targets.

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