A modified ni CoCrAlYTa bond coat and method of making the same

Abstract

The present application relates to the technical field of high-temperature oxidation-resistant coating, and particularly relates to a modified NiCoCrAlYTa bonding layer and a preparation method thereof.The present application adopts low-pressure plasma gas spraying to prepare a NiCoCrAlYTa bonding layer on the surface of a high-temperature alloy substrate, then performs shot peening treatment to reduce the surface roughness of the coating, then performs Al-Cr co-diffusion, and forms a co-diffusion bonding layer with an outer Al-rich layer, an intermediate Cr-rich layer and an inner NiCoCrAlYTa layer, finally performs vacuum pre-oxidation to form a TGO layer on the surface of the co-diffusion bonding layer, thereby obtaining the modified NiCoCrAlYTa bonding layer.The modified NiCoCrAlYTa bonding layer prepared by the present application has excellent high-temperature oxidation resistance and corrosion resistance, and can realize long-time service.

Description

Technical Field

[0001] This invention relates to the field of high-temperature antioxidant coating technology, and in particular to a modified NiCoCrAlYTa binder layer and its preparation method. Background Technology

[0002] Nickel-based single-crystal superalloys are widely used in core hot-end components such as turbine blades of aero-engines due to their excellent high-temperature mechanical properties and structural stability. However, the harsh service environment requires the materials to also have good resistance to high-temperature oxidation and hot corrosion. Superalloys themselves cannot meet these requirements at the same time. Thermal barrier coatings are often sprayed on the surface of superalloys to provide high-temperature protection.

[0003] MCrAlY (M is Ni, Co, or Ni+Co) coating is a commonly used metal bonding layer. It has excellent resistance to high-temperature oxidation and hot corrosion, good plasticity, and can be used alone as a top layer or as a base layer for thermal barrier coatings (TBC). Its composition is highly controllable.

[0004] In the MCrAlY coating system, different elements play different roles during high-temperature oxidation and thermal corrosion. Ni and Co, as the main elements, primarily enhance the coating's corrosion resistance while maintaining good toughness. Al and Cr mainly determine the coating's oxidation performance. Cr, while forming an oxide film, reduces the critical Al content required for Al2O3 film formation. Al combines with oxygen to form a dense α-Al2O3 protective film, preventing further oxidation. Y increases the adhesion of the surface oxide film, acting as a "pinning" effect, and also improves the coating's thermal shock resistance. The addition of Ta in the hexa-element alloy strengthens the γ' phase, increasing the coating's operating temperature, and traps oxygen, promoting Al2O3 formation and further enhancing the coating's oxidation resistance and adhesion.

[0005] Therefore, the hexa-element alloy coating NiCoCrAlYTa possesses excellent resistance to high-temperature oxidation and hot corrosion, as well as good mechanical properties, and is widely used in hot-end components such as aero-engine hot-end parts, heavy-duty and marine gas turbine turbine blades, and metallurgical furnace bottom rollers. It also has broad application prospects in hot-end components in the automotive and energy industries. However, due to coating preparation defects and harsh service environments, existing NiCoCrAlYTa bonding layers face the challenge of long-term service.

[0006] Figure 1This image shows the failure morphology of an existing NiCoCrAlYTa coating in a S- and Cl-rich hot corrosion environment. The corrosion progression is as follows: First, the alloy forms a TGO (thermally grown oxide: an oxide film formed by the metal bond layer in a high-temperature oxidative corrosion environment, consisting of α-Al₂O₃, spinel oxides, etc.) layer. Besides α-Al₂O₃, a large amount of spinel oxide is also formed in this layer, meaning a continuous and dense protective oxide film cannot be formed. In the S- and Cl-rich hot corrosion environment, the TGO layer is quickly destroyed, failing to provide long-term protection to the substrate. As the formed alumina is continuously destroyed, Al and Cr elements in the coating become depleted, and subsequently, other elements in the alloy are gradually oxidized and corroded, forming... Figure 1 (a) Middle layer c structure; all elements in the final alloy are oxidized and corroded, forming Figure 1 (a) The structure shown in the middle layer b is now completely oxidized and corroded, and gradually peels off under stress. Figure 1 (d) indicates the presence of sulfides (mainly Cr2S3) and oxides (mainly Al2O3) inside the coating. The sulfides are formed by the reaction of S elements diffusing into the coating with Cr. The formation of Cr2S3 fixes the S elements, thus preventing them from diffusing further into the coating. The oxides are formed by the reaction of metal chlorides with oxygen in areas of high oxygen partial pressure in the coating, at which point the coating undergoes internal oxidation.

[0007] In recent years, developing new preparation processes and improving coating quality have been important means to enhance the long-term service performance of NiCoCrAlYTa binders. The main methods for preparing NiCoCrAlYTa binders include electron beam physical vapor deposition (EB-PVD), atmospheric plasma spraying (APS), high-velocity vapor deposition (HVAF, HVOF, LT-HVOF), low-pressure plasma spraying (LPPS), arc ion plating (AIP), and magnetron sputtering (MS). Among these, low-pressure plasma spraying (LPPS), performed under vacuum or a protective atmosphere, boasts high deposition efficiency and produces coatings with low oxygen content, low porosity, high bonding strength, high chemical purity, and good high-temperature oxidation resistance, making it widely used in thermal barrier coating preparation. Low-temperature supersonic flame spraying (LT-HVOF) is a novel coating preparation process that not only reduces particle temperature but also increases particle velocity, reducing the binding of particles with oxygen in the air. This results in NiCoCrAlYTa coatings with high bonding strength and density, while maintaining an oxygen content comparable to LPPS coatings.

[0008] Both LPPS and LT-HVOF processes produce adhesive layers with high surface roughness, and the composition of the adhesive layers cannot be completely uniformly distributed. The high surface roughness of the coating leads to variations in oxygen content across different regions, resulting in uneven growth of thermally grown oxides (TGOs) (e.g., ...). Figure 3 As shown in (a), the TGO layer has a high standard deviation in thickness, which easily leads to localized cracking. On the other hand, multi-element corrosive media are prone to deposition, exacerbating the corrosion reaction. Therefore, the antioxidant and thermal corrosion resistance of the adhesive layers prepared by LPPS and LT-HVOF processes needs further improvement. Summary of the Invention

[0009] The purpose of this invention is to provide a modified NiCoCrAlYTa binder layer and its preparation method. The modified NiCoCrAlYTa binder layer prepared by this invention has excellent high-temperature oxidation resistance and corrosion resistance, and can achieve long-term service in hot corrosion environments rich in S and Cl.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for preparing a modified NiCoCrAlYTa binder layer, comprising the following steps:

[0012] A NiCoCrAlYTa bonding layer was prepared on the surface of a high-temperature alloy substrate by low-pressure plasma gas spraying to obtain the first high-temperature alloy substrate.

[0013] The first high-temperature alloy substrate is shot-peened to form a shot-peening stress layer on the surface of the NiCoCrAlYTa bonding layer, thereby obtaining the second high-temperature alloy substrate.

[0014] Chemical vapor infiltration of Cr and Al is performed sequentially on the surface of the shot-peened stress layer of the second high-temperature alloy matrix. Internal diffusion forms an Al-Cr co-infiltration bonding layer with an outer layer rich in Al, a middle layer rich in Cr, and an inner layer of NiCoCrAlYTa, thus obtaining the third high-temperature alloy.

[0015] The third high-temperature alloy is subjected to vacuum pre-oxidation to form a TGO layer on the surface of the co-diffusion bonding layer, thereby obtaining a modified NiCoCrAlYTa bonding layer.

[0016] Preferably, the conditions for low-pressure plasma spraying include: current of 600-700A, voltage of 60-65V, Ar flow rate of 55-65SLPM, H2 flow rate of 5-8SLPM, powder feeding rate of 1-1.6L / min, and spraying distance of 250-300mm.

[0017] Preferably, the NiCoCrAlYTa alloy powder used in the low-pressure plasma spraying comprises, by mass percentage, the following elements: Co 22-24%, Cr 19-21%, Al 7.5-9.5%, Y 0.4-0.8%, Ta 3.5-5.5%, and the balance Ni.

[0018] Preferably, the thickness of the NiCoCrAlYTa adhesive layer is 40–60 μm.

[0019] Preferably, the shot peening conditions include: the shot is glass shot with a particle size of 150-250 mesh, the shot peening pressure is 0.15-0.3 MPa, the shot peening time is 10-30 s, and the shot peening distance is 10-20 cm.

[0020] Preferably, the Cr diffusion conditions include: the Cr source is a pure chromium block, the carrier gas is argon with a flow rate of 4–6 SLPM, the reaction gas is hydrogen chloride with a flow rate of 0.5–1 SLPM, the Cr diffusion temperature is 950–1050 °C, and the initial vacuum degree is (1–5) × 10⁻⁶. - 3 The pressure for Cr infiltration is 5–10 kPa, and the infiltration time is 1–3 h.

[0021] Preferably, the Al infiltration conditions include: the Al source is a pure aluminum block, the carrier gas is hydrogen with a flow rate of 4–6 SLPM, the reaction gas is hydrogen chloride with a flow rate of 1–2 SLPM, the Al infiltration temperature is 950–1050°C, and the initial vacuum degree is (1–5) × 10⁻⁶. - 3 The Al infiltration pressure is 15–20 kPa, and the Al infiltration time is 1–3 h.

[0022] Preferably, the conditions for vacuum pre-oxidation include: a vacuum degree of 300-500 Pa, an argon to oxygen flow ratio of 180-220:1, a temperature of 850-900℃, and a holding time of 20-25 h.

[0023] The present invention provides a modified NiCoCrAlYTa binder layer prepared by the preparation method described above, which includes, from the outside to the inside, a TGO layer, an Al-rich outer layer, a Cr-rich intermediate layer and a NiCoCrAlYTa inner layer; the TGO layer is mainly composed of continuous and dense α-Al2O3.

[0024] Preferably, by mass percentage, the Al-rich outer layer contains 22-25% Al, 14-16% Co, 3-5% Cr, 0.1-1.0% Ta, with the balance being Ni; the Cr-rich intermediate layer contains 75-90% Cr, 6-8% Co, 1-3% Al, with the balance being Ni; and the NiCoCrAlYTa inner layer contains 22-24% Co, 19-21% Cr, 7.5-9.5% Al, 0.4-0.8% Y, 3.5-5.5% Ta, with the balance being Ni.

[0025] This invention provides a method for preparing a modified NiCoCrAlYTa binder layer, comprising the following steps: preparing a NiCoCrAlYTa binder layer by spraying a low-pressure plasma gas onto the surface of a high-temperature alloy substrate to obtain a first high-temperature alloy substrate; performing shot peening on the first high-temperature alloy substrate to form a shot peening stress layer on the surface of the NiCoCrAlYTa binder layer to obtain a second high-temperature alloy substrate; sequentially performing Cr and Al diffusion on the surface of the shot peening stress layer of the second high-temperature alloy substrate to form an Al-Cr co-diffusion binder layer with an outer Al-rich layer, a middle Cr-rich layer, and an inner NiCoCrAlYTa layer to obtain a third high-temperature alloy; and performing vacuum pre-oxidation on the third high-temperature alloy to form a TGO layer on the surface of the co-diffusion binder layer to obtain the modified NiCoCrAlYTa binder layer.

[0026] This invention involves shot peening the NiCoCrAlYTa binder layer prepared by LPPS, which can reduce the surface roughness of the coating by more than 50%, improve the surface density and smoothness of the coating, and prevent multi-element corrosive media from depositing and penetrating into the coating. During high-temperature oxidation, the coating after shot peening can reduce the inward diffusion of O atoms, thereby avoiding the occurrence of abnormal oxidation zones. The TGO layer grows slowly and has a more uniform thickness, thus improving its oxidation resistance.

[0027] The NiCoCrAlYTa bonding layer after shot peening is then subjected to chemical vapor infiltration of Cr and Al (referred to as Al-Cr chemical vapor infiltration) to obtain a three-layer Al-Cr co-infiltrated bonding layer. In a hot corrosion environment rich in S and Cl, the Al-rich outer layer can quickly form an α-Al2O3 protective film, improving the coating's oxidation resistance. The Cr-rich middle layer can improve the coating's resistance to hot corrosion and reduce the interdiffusion between the inner and outer coatings, promoting the formation of the α-Al2O3 film. Therefore, the Al-Cr co-infiltrated bonding layer can effectively improve the high-temperature oxidation resistance and hot corrosion resistance of the NiCoCrAlYTa bonding layer.

[0028] Following Al-Cr chemical vapor infiltration, the coating undergoes vacuum pre-oxidation. In the original TGO coating, besides α-Al₂O₃, a large amount of spinel oxide is formed; however, after vacuum pre-oxidation, the modified coating's TGO layer is dominated by α-Al₂O₃, effectively inhibiting the formation of spinel oxide during high-temperature oxidation, thus reducing the overall oxide film growth rate. Furthermore, vacuum pre-oxidation improves the bonding between coating particles, increasing coating density and making it more difficult for S and Cl elements to diffuse into the coating. Simultaneously, the continuous and dense oxide film on the vacuum pre-oxidized coating surface more effectively slows down the diffusion of S and Cl elements into the coating, reducing the degree of corrosion and thus effectively improving the coating's corrosion resistance. Attached Figure Description

[0029] Figure 1 The failure morphology of the existing NiCoCrAlYTa coating in a hot corrosion environment rich in S and Cl is shown. Among them, (a) is the overall morphology of the failed coating, (b) is the morphology of the middle layer b in (a), (c) is the morphology of the middle layer c in (a), and (d) is the morphology of the middle layer d in (a).

[0030] Figure 2 The cross-sectional morphology of the original coating and the modified NiCoCrAlYTa bonding layer is shown, where (a) is the original coating and (b) is the modified NiCoCrAlYTa bonding layer.

[0031] Figure 3 The distribution of alumina film was observed by EDS surface scanning of the original coating and the modified NiCoCrAlYTa bonding layer, where (a) is the original coating and (b) is the modified coating.

[0032] Figure 4 Flowchart of the preparation method of modified NiCoCrAlYTa binder layer;

[0033] Figure 5 EDS surface scan of the cross section of the modified NiCoCrAlYTa binder layer;

[0034] Figure 6 Diagram of the modified NiCoCrAlYTa binder layer;

[0035] Figure 7 The surface profile curves of the original coating and the modified NiCoCrAlYTa adhesive layer;

[0036] Figure 8 These are the results of a cyclic oxidation experiment;

[0037] Figure 9 This is a curve showing the amount of oxide film detached during the cyclic oxidation process;

[0038] Figure 10 The cyclic oxidation kinetics curve;

[0039] Figure 11 The results are from the salt coating hot corrosion test.

[0040] Figure 12 The kinetic curve of salt coating thermal corrosion;

[0041] Figure 13 The surface morphology after 3000 thermal shock and air cooling tests is shown in (a) the macroscopic morphology of the original coating, (b) the secondary electronic morphology of the original coating, (c) the macroscopic morphology of the modified NiCoCrAlYTa binder layer, and (d) the secondary electronic morphology of the modified NiCoCrAlYTa binder layer.

[0042] Figure 14The surface morphology after 50 thermal shock and water quenching experiments is shown in (a) the macroscopic morphology of the original coating, (b) the secondary electronic morphology of the original coating, (c) the macroscopic morphology of the modified NiCoCrAlYTa binder layer, and (d) the secondary electronic morphology of the modified NiCoCrAlYTa binder layer. Detailed Implementation

[0043] like Figure 4 As shown, this invention provides a method for preparing a modified NiCoCrAlYTa binder layer, comprising the following steps:

[0044] A NiCoCrAlYTa bonding layer was prepared on the surface of a high-temperature alloy substrate by low-pressure plasma gas spraying to obtain the first high-temperature alloy substrate.

[0045] The first high-temperature alloy substrate is shot-peened to form a shot-peening stress layer on the surface of the NiCoCrAlYTa bonding layer, thereby obtaining the second high-temperature alloy substrate.

[0046] Chemical vapor infiltration of Cr and Al is performed sequentially on the surface of the shot-peened stress layer of the second high-temperature alloy matrix. Internal diffusion forms an Al-Cr co-infiltration bonding layer with an outer layer rich in Al, a middle layer rich in Cr, and an inner layer of NiCoCrAlYTa, thus obtaining the third high-temperature alloy.

[0047] The third high-temperature alloy is subjected to vacuum pre-oxidation to form a TGO layer on the surface of the co-diffusion bonding layer, thereby obtaining a modified NiCoCrAlYTa bonding layer.

[0048] This invention uses low-pressure plasma gas spraying to prepare a NiCoCrAlYTa bonding layer on the surface of a high-temperature alloy substrate, thereby obtaining a first high-temperature alloy substrate.

[0049] In this invention, the high-temperature alloy substrate preferably comprises a nickel-based high-temperature alloy substrate. Before preparing the NiCoCrAlYTa bonding layer, the high-temperature alloy substrate is preferably subjected to wire cutting, grinding, rounding, sandblasting, cleaning, and drying in sequence. In this invention, wire cutting is used to process block or rod-shaped high-temperature alloys into experimental samples of a certain size (in this embodiment, a cylindrical sample with a diameter of φ10×10). Grinding is used to remove oxides generated during wire cutting. Rounding is used to reduce edge effects and improve stress concentration during coating preparation. Sandblasting is used to enhance the adhesion between the coating and the substrate alloy. Cleaning is used to remove residual impurities from the sample surface to avoid affecting the experimental results. In this invention, grinding is preferably performed sequentially using 200#, 600#, and 800# wet sandpaper to grind each surface of the substrate. Preferably, the grinding is performed until the roughness Ra of each surface of the substrate is less than 0.8. In this invention, the fine sand used for sandblasting is preferably 150 mesh, and the sandblasting pressure is preferably 0.2 MPa. This invention does not impose any special limitations on the processes of rounding, cleaning, and drying; processes well-known in the art can be followed.

[0050] In this invention, the NiCoCrAlYTa alloy powder used for low-pressure plasma spraying preferably includes the following elements by mass percentage: Co 22-24%, Cr 19-21%, Al 7.5-9.5%, Y 0.4-0.8%, Ta 3.5-5.5%, and the balance Ni.

[0051] In this invention, the preferred conditions for low-pressure plasma spraying include: a current of 600–700 A, a voltage of 60–65 V, an Ar flow rate of 55–65 SLPM, an H2 flow rate of 5–8 SLPM, a powder feed rate of 1–1.6 L / min, and a spraying distance of 250–300 mm. More specifically, the preferred current for low-pressure plasma spraying is 620–680 A, more preferably 640–660 A; the preferred Ar flow rate is 58–62 SLPM; the preferred H2 flow rate is 6–7 SLPM; the preferred powder feed rate is 1.2–1.4 L / min; and the preferred spraying distance is 260–280 mm.

[0052] In this invention, the thickness of the NiCoCrAlYTa adhesive layer is preferably 40-60 μm, more preferably 45-55 μm.

[0053] After obtaining the first high-temperature alloy substrate, the present invention performs shot peening on the first high-temperature alloy substrate to form a shot peening stress layer on the surface of the NiCoCrAlYTa bonding layer, thereby obtaining the second high-temperature alloy substrate.

[0054] In this invention, the preferred conditions for shot peening include: glass pellets with a particle size of 150–250 mesh, shot peening pressure of 0.15–0.3 MPa, shot peening time of 10–30 s, and shot peening distance of 10–20 cm. More specifically, the preferred particle size of the shot is 200 mesh; the preferred shot peening pressure is 0.2–0.25 MPa; the preferred shot peening time is 15–25 s; and the preferred shot peening distance is 14–16 cm.

[0055] The present invention performs shot peening on the NiCoCrAlYTa bonding layer, which can reduce the surface roughness of the coating by more than 50%, improve the surface density and smoothness of the coating, and prevent multi-element corrosive media from depositing and penetrating into the coating. During the high-temperature oxidation process, the coating after shot peening can reduce the inward diffusion of O atoms, thereby avoiding the occurrence of abnormal oxidation zones. The TGO layer grows slowly and has a more uniform thickness, thus improving the oxidation resistance.

[0056] After obtaining the second high-temperature alloy substrate, the present invention sequentially performs chemical vapor infiltration of Cr and Al on the surface of the shot-peened stress layer of the second high-temperature alloy substrate, and internal diffusion forms an Al-Cr co-infiltration bonding layer with an outer layer rich in Al, a middle layer rich in Cr, and an inner layer of NiCoCrAlYTa, to obtain the third high-temperature alloy.

[0057] In this invention, the preferred conditions for Cr infiltration include: a pure chromium block as the Cr source, argon as the carrier gas with a flow rate of 4–6 SLPM, hydrogen chloride as the reaction gas with a flow rate of 0.5–1 SLPM, an infiltration temperature of 950–1050 °C, and an initial vacuum of (1–5) × 10⁻⁶. -3 The pressure for Cr infiltration is 5–10 kPa, and the infiltration time is 1–3 h.

[0058] In this invention, the preferred conditions for Al infiltration include: the Al source is a pure aluminum block, the carrier gas is hydrogen with a flow rate of 4–6 SLPM, the reaction gas is hydrogen chloride with a flow rate of 1–2 SLPM, the Al infiltration temperature is 950–1050°C, and the initial vacuum degree is (1–5) × 10⁻⁶. -3 The Al infiltration pressure is 15–20 kPa, and the Al infiltration time is 1–3 h.

[0059] This invention employs a process of first infiltrating Cr and then Al, resulting in an Al-Cr co-diffusion bonding layer with an outer Al-rich outer layer, a middle Cr-rich middle layer, and an inner NiCoCrAlYTa layer. In a hot-corrosion environment rich in S and Cl, the Al-rich outer layer can quickly form an α-Al₂O₃ protective film, improving the coating's oxidation resistance. The Cr-rich middle layer enhances the coating's resistance to hot corrosion and reduces interdiffusion between the inner and outer coatings, promoting the formation of the α-Al₂O₃ film. Therefore, the Al-Cr co-diffusion bonding layer effectively improves the high-temperature oxidation and hot corrosion resistance of the NiCoCrAlYTa bonding layer.

[0060] After obtaining the third high-temperature alloy, the present invention performs vacuum pre-oxidation on the third high-temperature alloy to form a TGO layer on the surface of the co-diffusion bonding layer, thereby obtaining a modified NiCoCrAlYTa bonding layer.

[0061] In this invention, the preferred conditions for vacuum pre-oxidation include: a vacuum degree of 300–500 Pa, an argon to oxygen flow rate ratio of 180–220:1, a temperature of 850–900 °C, and a holding time of 20–25 h. Further, the vacuum pre-oxidation temperature is more preferably 860–880 °C, the holding time is more preferably 22–23 h, and the argon to oxygen flow rate ratio is more preferably 190–210:1.

[0062] This invention employs vacuum pre-oxidation treatment, resulting in a TGO layer primarily composed of α-Al₂O₃. This effectively inhibits the formation of spinel oxides during high-temperature oxidation, thereby reducing the overall oxide film growth rate. Furthermore, vacuum pre-oxidation improves the bonding between coating particles, increasing coating density and making it more difficult for S and Cl elements to diffuse into the coating. Simultaneously, the continuous and dense oxide film on the vacuum pre-oxidized coating surface more effectively slows down the diffusion of S and Cl elements into the coating, reducing the degree of corrosion and thus effectively improving the coating's corrosion resistance.

[0063] The present invention provides a modified NiCoCrAlYTa binder layer prepared by the preparation method described above, which includes, from the outside to the inside, a TGO layer, an Al-rich outer layer, a Cr-rich intermediate layer and a NiCoCrAlYTa inner layer; the TGO layer is mainly composed of continuous and dense α-Al2O3.

[0064] In this invention, the thickness of the TGO layer is preferably 0.8–1.2 μm; the thickness of the Al-rich outer layer is preferably 5–10 μm; the thickness of the Cr-rich intermediate layer is preferably 5–10 μm; and the thickness of the NiCoCrAlYTa inner layer is preferably 30–40 μm.

[0065] In this invention, based on mass percentage, the Al-rich outer layer preferably contains 22-25% Al, 14-16% Co, 3-5% Cr, and 0.1-1.0% Ta, with the balance being Ni; the Cr-rich intermediate layer preferably contains 75-90% Cr, 6-8% Co, and 1-3% Al, with the balance being Ni; and the NiCoCrAlYTa inner layer preferably contains 22-24% Co, 19-21% Cr, 7.5-9.5% Al, 0.4-0.8% Y, and 3.5-5.5% Ta, with the balance being Ni.

[0066] The modified NiCoCrAlYTa binder layer and its preparation method provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] A nickel-based superalloy substrate was cut into cylindrical samples with dimensions of φ10mm×10mm using wire cutting. A groove was cut in the middle of the sample to facilitate suspension on a support during coating preparation. Then, each surface of the substrate was polished sequentially using 200#, 600#, and 800# wet sandpaper until the surface roughness Ra of each surface was less than 0.8. The polished substrate was then sandblasted with 150-mesh fine sand at a pressure of 0.2MPa. Finally, the obtained substrate was rounded, cleaned, and dried to obtain a pretreated substrate.

[0069] Low-pressure plasma spraying (LPPS) was performed on the surface of the pretreated substrate to prepare a NiCoCrAlYTa bonding layer, denoted as the initial coating. The NiCoCrAlYTa alloy powder used comprised the following elements by mass percentage: Co 23%, Cr 20%, Al 8.5%, Y 0.8%, Ta 4.5%, and the balance Ni. The LPPS was performed with a current of 650 A, a voltage of 65 V, an Ar flow rate of 60 SLPM, an H2 flow rate of 6 SLPM, a powder feed rate of 1.3 L / min, and a spraying distance of 270 mm. The thickness of the NiCoCrAlYTa layer was 46 μm.

[0070] The NiCoCrAlYTa bonding layer was shot peened with a shot size of 200 mesh, a shot peening pressure of 0.2 MPa, a shot peening time of 15 s, and a shot peening distance of 15 cm. This reduced the surface roughness of the coating while obtaining a relatively dense shot-peened stress layer.

[0071] Al-Cr chemical vapor infiltration was performed on the surface of the shot-peened stress layer. The Al-Cr chemical vapor infiltration was performed in two steps: first Cr infiltrates, then Al infiltrates. The conditions for Cr infiltration were: the Cr source was a pure chromium block; the carrier gas was argon at a flow rate of 5 SLPM; the reactant gas was hydrogen chloride at a flow rate of 0.5 SLPM; the Cr infiltration temperature was 1000℃; and the initial vacuum was 2 × 10⁻⁶. -3 The Cr diffusion pressure was 5 kPa, and the diffusion time was 2.5 h. The Al source for Al diffusion was a pure aluminum block, the carrier gas was hydrogen with a flow rate of 5 SLPM, the reactant gas was hydrogen chloride with a flow rate of 1.6 SLPM, the temperature was 1000℃, and the initial vacuum was 2 × 10⁻⁶. -3 Pa, Al diffusion pressure of 20 kPa, time of 2.5 h, internal diffusion forms an Al-Cr co-diffusion bonding layer with an outer layer rich in Al, a middle layer rich in Cr, and an inner layer with a composition similar to the original NiCoCrAlYTa bonding layer; the thickness of the outer layer is 6 μm, the thickness of the middle layer is 5 μm, and the thickness of the inner layer is 34 μm.

[0072] By mass percentage, the outer layer contains 22% Al, 15% Co, and 5% Cr, with the balance being Ni; the middle layer contains 80% Cr, 7% Co, and 2% Al, with the balance being Ni; the inner layer has a composition basically the same as the original NiCoCrAlYTa bonding layer, with 20% Co, 21% Cr, 13.5% Al, 0.7% Y, and 4.3% Ta, with the balance being Ni.

[0073] The Al-Cr co-diffusion bonding layer was subjected to vacuum pre-oxidation treatment. The vacuum degree of the pre-oxidation treatment was 350 Pa, the argon to oxygen flow ratio was 995:5, the temperature was 870℃, the heating rate was 5℃ / min, and the holding time was 24h. A continuous and dense protective oxide film mainly composed of α-Al2O3 was grown on its surface. Figure 3 (b) Figure 5 and Figure 6 As shown.

[0074] Figure 5 EDS surface scan of the cross section of the modified NiCoCrAlYTa binder layer. Figure 6 This is a structural diagram of the modified NiCoCrAlYTa binder layer. Figure 5 and Figure 6It can be clearly seen that the modified NiCoCrAlYTa binder layer prepared by the present invention includes a continuous and dense TGO layer, an Al-rich outer layer, a Cr-rich intermediate layer, and a original NiCoCrAlYTa inner layer; the thickness of the TGO layer is 1 μm, the thickness of the Al-rich outer layer is 6 μm, the thickness of the Cr-rich intermediate layer is 5 μm, and the thickness of the NiCoCrAlYTa inner layer is 34 μm.

[0075] Figure 2 The cross-sectional morphology of the original coating and the modified NiCoCrAlYTa bonding layer is shown, where (a) is the original coating and (b) is the modified NiCoCrAlYTa bonding layer. Figure 7 These are surface profile curves of two coatings drawn based on surface roughness data; Figure 2 and Figure 7 It can be seen that the surface roughness of the coating decreased significantly after shot peening. The Ra values ​​of the modified NiCoCrAlYTa binder layer measured by the profilometer are as follows: 2885.81, 3032.6, 2550.04, 2669.74, 3041.82 (nm). The surface roughness of the original coating was relatively high. The Ra values ​​of the original coating layer measured by the profilometer are as follows: 6791.83, 6954.56, 6347.61, 6928.21, 7231.69 (nm). This indicates that shot peening can reduce the surface roughness of the coating.

[0076] Performance testing:

[0077] (1) Antioxidant performance evaluation

[0078] In accordance with the requirements of HB5258-2000 "Test Method for Determination of Oxidation Resistance of Steel and High-Temperature Alloys", high-temperature cyclic oxidation performance tests of 1050℃ / 200h were conducted on samples of original NiCoCrAlYTa coating, shot peening + pre-oxidation modified coating, and shot peening + Al-Cr co-diffusion + pre-oxidation modified coating. The surface condition of the samples after the test was analyzed and studied, the oxidation rate was recorded, and the oxidation resistance of the coating was evaluated.

[0079] Figure 8 The morphologies of the samples after cyclic oxidation for 0 h, 100 h, and 200 h are shown respectively. It can be seen that after the same cyclic oxidation time, the amount of oxide film detachment is: original coating > shot peening + pre-oxidation modified coating > shot peening + Al-Cr co-diffusion + pre-oxidation modified coating. This is from... Figure 9 This can be confirmed by the oxide film shedding curve shown.

[0080] Figure 10 The oxidation kinetics curves are shown after 200 hours of cyclic oxidation. The original coating only experienced rapid weight gain in the first hour, and then remained in a state of weight loss; the average oxide scale shedding amount throughout the entire test cycle was 24.31 g / m². 2The average oxidation rate is 0.03 g / m. 2 According to the HB5258-2000 antioxidant rating, the coating should be rated as secondary antioxidant. The shot peening + pre-oxidation modified coating and the shot peening + Al-Cr co-diffusion + pre-oxidation modified coating showed a slow weight gain throughout the 200-hour test; the average oxide scale shedding amount was 4.99 g / m² and 0.85 g / m², respectively, over the entire test period. 2 The average oxidation rates were 0.075 and 0.027 g / m. 2 According to the HB5258-2000 antioxidant rating, h is classified as antioxidant and fully antioxidant, respectively.

[0081] (2) Evaluation of hot corrosion resistance

[0082] In accordance with the requirements of HB20401-2016 "Salt Corrosion Test Method", salt corrosion tests were conducted at 900℃ for 100h on samples of original coating, shot peening + pre-oxidation modified coating, and shot peening + Al-Cr co-diffusion + pre-oxidation modified coating under artificial seawater corrosive medium conditions. The surface condition of the samples after the test was analyzed and studied, the corrosion rate was recorded, and the coating's resistance to hot corrosion was evaluated.

[0083] Figure 11 The images show the morphology of the samples after 2 and 5 cycles of salt-coated hot corrosion. After 2 cycles, the shot-peening + Al-Cr co-diffusion + pre-oxidation modified coating still maintained good gloss, while the shot-peening + pre-oxidation modified coating lost its gloss, and the original coating showed obvious hot corrosion morphology. After 5 cycles, flaking corrosion products were detected in the original coating, and a small amount of corrosion products were also detected in the shot-peening + pre-oxidation modified coating, while no corrosion products were detected in the shot-peening + Al-Cr co-diffusion + pre-oxidation modified coating.

[0084] Figure 12 The figures show the corrosion kinetics curves for salt thermal corrosion. The original coating showed weight gain only in the first cycle, followed by continuous weight loss. The shot-peened + pre-oxidized modified coating showed weight gain in the first three cycles, followed by weight loss. The shot-peened + Al-Cr co-diffusion + pre-oxidized modified coating showed weight gain throughout all five cycles. This indicates that the shot-peened + Al-Cr co-diffusion + pre-oxidized modified coating exhibits good resistance to thermal corrosion.

[0085] (3) Thermal shock resistance performance assessment

[0086] Thermal shock tests were conducted on the original coating and the shot-peened + Al-Cr co-diffusion + pre-oxidation modified coating samples. The number of thermal shock cycles at which the coating began to wrinkle, crack, peel, and detach was recorded to evaluate the thermal shock resistance of the coating.

[0087] ① Air cooling: Temperature 1050℃±10℃, hold for 5~10min, then air cool for 5min;

[0088] like Figure 13 As shown, after 3000 cycles, the original coating surface was loose and showed obvious cracks and peeling; while the modified coating surface remained smooth and dense, with no cracks detected. Figure 13 In the figures, (a) the macroscopic morphology of the original coating, (b) the secondary electronic morphology of the original coating, (c) the macroscopic morphology of the modified NiCoCrAlYTa binder layer, and (d) the secondary electronic morphology of the modified NiCoCrAlYTa binder layer.

[0089] ② Water quenching: Temperature 1050℃±10℃, hold for 5~10min, then quickly quench in water at 20±5℃ for 5~8s;

[0090] like Figure 14 As shown, after 50 cycles, the original coating surface showed obvious peeling, while the modified coating surface remained intact. Figure 14 In the figures, (a) the macroscopic morphology of the original coating, (b) the secondary electronic morphology of the original coating, (c) the macroscopic morphology of the modified NiCoCrAlYTa binder layer, and (d) the secondary electronic morphology of the modified NiCoCrAlYTa binder layer.

[0091] In summary, this invention improves the high-temperature oxidation resistance, hot corrosion resistance, and thermal shock resistance of the original NiCoCrAlYTa coating by sequentially performing shot peening, Al-Cr co-infiltration, and vacuum pre-oxidation.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a modified NiCoCrAlYTa binder layer, characterized in that, Includes the following steps: A NiCoCrAlYTa bonding layer was prepared on the surface of a high-temperature alloy substrate by low-pressure plasma gas spraying to obtain the first high-temperature alloy substrate. The first high-temperature alloy substrate is shot-peened to form a shot-peening stress layer on the surface of the NiCoCrAlYTa bonding layer, thereby obtaining the second high-temperature alloy substrate. Chemical vapor infiltration of Cr and Al is performed sequentially on the surface of the shot-peened stress layer of the second high-temperature alloy matrix. Internal diffusion forms an Al-Cr co-infiltration bonding layer with an outer layer rich in Al, a middle layer rich in Cr, and an inner layer of NiCoCrAlYTa, thus obtaining the third high-temperature alloy. The third high-temperature alloy is subjected to vacuum pre-oxidation to form a TGO layer on the surface of the co-diffusion bonding layer, thereby obtaining a modified NiCoCrAlYTa bonding layer.

2. The preparation method according to claim 1, characterized in that, The conditions for low-pressure plasma spraying include: current of 600-700A, voltage of 60-65V, Ar flow rate of 55-65SLPM, H2 flow rate of 5-8SLPM, powder feeding rate of 1-1.6L / min, and spraying distance of 250-300mm.

3. The preparation method according to claim 1 or 2, characterized in that, The NiCoCrAlYTa alloy powder used in the low-pressure plasma spraying comprises, by mass percentage, the following elements: Co 22-24%, Cr 19-21%, Al 7.5-9.5%, Y 0.4-0.8%, Ta 3.5-5.5%, and the balance Ni.

4. The preparation method according to claim 1 or 2, characterized in that, The thickness of the NiCoCrAlYTa adhesive layer is 40–60 μm.

5. The preparation method according to claim 1, characterized in that, The conditions for shot peening include: the shot material is glass shot with a particle size of 150-250 mesh, the shot peening pressure is 0.15-0.3 MPa, the shot peening time is 10-30 s, and the shot peening distance is 10-20 cm.

6. The preparation method according to claim 1, characterized in that, The conditions for Cr infiltration include: the Cr source is a pure chromium block; the carrier gas is argon with a flow rate of 4–6 SLPM; the reactant gas is hydrogen chloride with a flow rate of 0.5–1 SLPM; the Cr infiltration temperature is 950–1050 °C; and the initial vacuum degree is (1–5) × 10⁻⁶. -3 The pressure for Cr infiltration is 5–10 kPa, and the infiltration time is 1–3 h.

7. The preparation method according to claim 1 or 6, characterized in that, The conditions for Al infiltration include: the Al source is a pure aluminum block; the carrier gas is hydrogen with a flow rate of 4–6 SLPM; the reaction gas is hydrogen chloride with a flow rate of 1–2 SLPM; the Al infiltration temperature is 950–1050 °C; and the initial vacuum degree is (1–5) × 10⁻⁶. -3 The Al infiltration pressure is 15–20 kPa, and the Al infiltration time is 1–3 h.

8. The preparation method according to claim 1, characterized in that, The conditions for vacuum pre-oxidation include: a vacuum degree of 300–500 Pa, an argon to oxygen flow ratio of 180–220:1, a temperature of 850–900 °C, and a holding time of 20–25 h.

9. The modified NiCoCrAlYTa binder layer prepared by the preparation method according to any one of claims 1 to 8, characterized in that, From the outside to the inside, it includes a TGO layer, an Al-rich outer layer, a Cr-rich intermediate layer, and a NiCoCrAlYTa inner layer; the TGO layer is mainly composed of continuous and dense α-Al2O3.

10. The modified NiCoCrAlYTa binder layer according to claim 9, characterized in that, By mass percentage, the Al-rich outer layer contains 22-25% Al, 14-16% Co, 3-5% Cr, 0.1-1.0% Ta, with the balance being Ni; the Cr-rich intermediate layer contains 75-90% Cr, 6-8% Co, 1-3% Al, with the balance being Ni; and the NiCoCrAlYTa inner layer contains 22-24% Co, 19-21% Cr, 7.5-9.5% Al, 0.4-0.8% Y, 3.5-5.5% Ta, with the balance being Ni.

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