Preparation method of high-entropy alloy coating with high oxidation resistance

Abstract

The invention discloses a preparation method of a high-entropy alloy coating with high oxidation resistance, and belongs to the field of coating preparation. Comprising the following steps that (1) gradient components are designed, a magnetron sputtering technology is adopted, coating deposition is conducted on a base body, and a high-entropy alloy coating is formed; the alloy coating comprises a surface layer, a middle layer and an inner layer, and the element contents of Mn and Cr in each layer are as follows: the surface layer comprises 15-25at.% of Mn and 1t of Cr; the middle layer comprises 10-15 at.% of Mn and 10-25 at.% of Cr, and the inner layer comprises Mnlt, 10-15 at.% of Mn and 10-25 at.% of Cr; %, Cr < gt >; %, 25 at. (2) pre-oxidation treatment: performing oxidation induction at the temperature of 700-800 DEG C and under the oxygen partial pressure of 10 <-4 >-10 <-3 > atm to form an oxidation film; through gradient enrichment design and induced oxidation treatment, a composite oxidation protection film which is compact in structure and high in thermal stability can be generated from the surface layer to the inner layer of the coating, and the oxidation resistance and the service reliability of the high-entropy alloy coating in a high-temperature environment are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating preparation, and more specifically, relates to a method for preparing a high-entropy alloy coating with high oxidation resistance. Background Art

[0002] High-entropy alloys (HEAs) are a class of alloy systems composed of five or more principal elements in equal atomic ratios. Their unique multi-principal element design and high mixing entropy effect impart excellent mechanical properties, thermal stability, corrosion resistance, and radiation resistance. In recent years, with the increasing demands placed on material performance in high-temperature, extreme environments such as aerospace, energy equipment, and metallurgical manufacturing, HEAs and their derived coatings have garnered widespread attention and become a key development direction for the next generation of high-performance structural materials.

[0003] In order to cope with the damage to the surface of structural materials caused by harsh environments such as high-temperature oxidation and high-temperature corrosion, researchers generally use high-entropy alloy coatings (such as laser cladding, thermal spraying, magnetron sputtering, etc.) to strengthen the surface of metal substrates to extend service life and improve overall reliability. These coatings, with their compositional adjustability and thermodynamic stability, are expected to form protective oxide films (such as Al2O3, Cr2O3) at high temperatures, thereby blocking oxygen diffusion and inhibiting further oxidation. However, existing high-entropy alloy coatings still face many challenges in practical applications, mainly reflected in the following aspects:

[0004] The distribution of antioxidant elements lacks a gradient design: Currently, most high-entropy alloy coatings adopt a uniform composition structure, and the distribution of antioxidant elements (such as Al, Cr, Si, Y, etc.) in the coating is relatively even, making it difficult to achieve surface enrichment. As a result, a dense and stable protective film cannot be preferentially generated in the early stage of oxidation, reducing the antioxidant efficiency.

[0005] The oxide film formation process is uncontrollable: During high-temperature oxidation, the oxide film often exhibits problems such as non-uniform growth, many holes, and coarse grains, making it difficult to achieve densification and stable interface bonding. The film layer has many initial defects, further reducing its protective effect.

[0006] Insufficient film adhesion and thermal shock resistance: The bonding between traditional oxide films and coatings is weak, and they are prone to failure forms such as cracks and peeling under thermal cycling or mechanical load conditions, seriously affecting the long-term stability and service life of the film.

[0007] For example, Chinese patent application number CN202211408032.6, published on January 10, 2023, discloses a high-hardness, high-wear-resistant high-entropy alloy coating and its preparation method. The alloy has the formula AlCoCrMoVx, where x is 0-1. The resulting AlCoCrMoVx high-entropy alloy coating exhibits high hardness and excellent wear resistance, and forms a black oxide film during electrochemical corrosion.

[0008] Another example is a Chinese patent application with the number CN202411082002.X, published on November 21, 2024, which discloses a high-entropy alloy coating, its preparation method, and application. The method comprises the following steps: S1: Using Fe, Co, Ni, Cr, Al, and Cu with a purity of 99.99% or more as raw materials, spherical powders are formed by ball milling or vacuum atomization to obtain FeCoNiCrCu or FeCoNiCrAlCu high-entropy alloy powders; S2: Laser cladding equipment is used to clad the high-entropy alloy powder obtained in S1 onto the surface of 304 stainless steel to obtain a FeCoNiCrCu or FeCoNiCrAlCu alloy coating. During the corrosion process, the internal FeCoNiCrAlCu alloy coating of this invention has a double-layer oxide film structure of Al2O3 and Cr2O3.

[0009] Both of the above schemes are high-entropy alloy coatings that generate oxide films. However, as can be seen from the specifications of the high-entropy alloy coatings of the two schemes, they both have the aforementioned problems of lack of gradient design of antioxidant element distribution, uncontrollable oxide film formation process, and insufficient film adhesion and heat shock resistance. Summary of the Invention

[0010] 1. Problems to be solved

[0011] In response to the problems of lack of gradient design in the distribution of antioxidant elements in existing high-entropy alloy coatings, uncontrollable oxidation film formation process, and insufficient film adhesion and thermal shock resistance, the present invention provides a method for preparing a high-entropy alloy coating with high oxidation resistance. Through gradient enrichment design and induced oxidation treatment, a composite oxidation protective film with dense structure and strong thermal stability can be generated from the surface to the inner layer of the coating, significantly improving the oxidation resistance and service reliability of the high-entropy alloy coating in high-temperature environments.

[0012] 2. Technical solution

[0013] To solve the above problems, the present invention adopts the following technical solutions.

[0014] A method for preparing a high-entropy alloy coating with high oxidation resistance comprises the following steps:

[0015] (1) Gradient composition design

[0016] The coating was deposited on the substrate using magnetron sputtering technology. During the preparation process, the Cr target power was gradually reduced and the Mn target power was gradually increased in stages to form a high-entropy alloy coating on the substrate surface.

[0017] The alloy coating comprises a surface layer, a middle layer and a bottom layer, and the element contents of Mn and Cr in each layer are as follows: surface layer: Mn: 15-25at.%, Cr<10at.%, middle layer: Mn: 10-15at.%, Cr: 10 -25at.%, bottom layer: Mn<10at.%, Cr>25at.%;

[0018] (2) Pre-oxidation treatment

[0019] At a temperature of 700–800°C and an oxygen partial pressure of 10 -4 –10 -3 Oxidation is induced under atm to form an oxide film.

[0020] As a further improvement of the technical solution, in step (1), the coating deposition includes three stages: a bottom layer stage: the Cr target power is 140-150 W, the Mn target power is 60-70 W, and the deposition time is 10-15 min; a middle layer stage: the Cr target power is 115-125 W, the Mn target power is 95-105 W, and the deposition time is 10-15 min; and a surface layer stage: the Cr target power is 85-95 W, the Mn target power is 130-140 W, and the deposition time is 10-15 min.

[0021] As a further improvement of the technical solution, the total thickness of the high entropy alloy coating is 30-35um, and the thickness of the middle layer accounts for 60-70% of the total coating thickness.

[0022] As a further improvement of the technical solution, in step (1), the coating deposition atmosphere is argon + 3-7% O2.

[0023] As a further improvement of the technical solution, in step (1), the working gas pressure for coating deposition is 0.4-0.6 Pa, and the total gas flow rate is 10-15 sccm.

[0024] As a further improvement of the technical solution, in step (1), the distance between the target and the substrate is 120-150 mm.

[0025] As a further improvement of the technical solution, in step (1), the deposition temperature is controlled between room temperature and 350°C.

[0026] As a further improvement of the technical solution, in step (2), the heating rate is controlled at 5°C / min, the oxygen flow rate is 0.4-0.8 sccm, and the holding time is 40-90 min.

[0027] As a further improvement of the technical solution, the oxide film is a surface layer of MnO x , a gradient film structure formed by the middle layer MnCr2O4 and the inner layer Cr2O3.

[0028] As a further improvement of the technical solution, the method further includes step (3), wherein after the oxide film is formed, the coating surface is strengthened by any one of shot peening, laser shock strengthening and ultrasonic rolling.

[0029] 3. Beneficial effects

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention provides a method for preparing a high-entropy alloy coating with high oxidation resistance. Through gradient enrichment design and thermodynamically induced oxidation treatment, the surface high Mn area preferentially forms Mn2O2 / Mn2O3 to improve oxygen affinity, the middle layer generates MnCr2O4 spinel and Cr2O3 phase to synergistically inhibit oxygen diffusion, and the bottom Cr-rich area further promotes the construction of a dense Cr2O skeleton, ultimately achieving external MnO x + The gradient multi-phase synergistic film structure of the middle MnCr2O4 + internal Cr2O3 has a dense film structure and uniform grains. Compared with the traditional multi-component oxide system, it has a lower oxidation rate and better interface integrity. The oxidation rate is reduced by more than 70%, and the porosity of the oxide film is less than 0.5%, effectively blocking external oxygen diffusion and interface reaction;

[0032] (2) The present invention provides a method for preparing a high-entropy alloy coating with high oxidation resistance, which uses shot peening, laser shock and other means to mechanically strengthen the oxide film, which can effectively improve the adhesion strength and microstructural integrity of the oxide film, making it less likely to produce failure modes such as peeling and flaking under multiple thermal-mechanical cyclic stresses. Test results show that the bonding strength of the film layer is improved by more than 70%, and the number of thermal shock cycles is increased to more than 1,000 times, which is 2-3 times that of conventional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the high entropy alloy coating structure of the present invention;

[0034] Figure 2 The figure is a flow chart of the method for preparing a high entropy alloy coating of the present invention. DETAILED DESCRIPTION

[0035] Exemplary embodiments of the present invention are described in detail below. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and that various changes may be made to the invention without departing from the spirit and scope of the invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the claimed invention, but is merely for illustrative and non-limiting purposes, to describe the features and characteristics of the invention, to set forth the best mode for carrying out the invention, and to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is limited solely by the appended claims.

[0036] The present invention provides a method for preparing a high-entropy alloy coating with high oxidation resistance, comprising the following steps:

[0037] (1) Gradient composition design

[0038] Magnetron sputtering technology is used to deposit the coating on the substrate. During the preparation process, the Cr target power is gradually reduced and the Mn target power is gradually increased in stages, forming a high-entropy alloy coating on the substrate surface. Specifically, the coating deposition consists of three stages: the bottom layer stage: the Cr target power is 140-150W, the Mn target power is 60-70W, and the deposition time is 10-15 minutes; the middle layer stage: the Cr target power is 115-125W, the Mn target power is 95-105W, and the deposition time is 10-15 minutes; the surface layer stage: the Cr target power is 85-95W, the Mn target power is 130-140W, and the deposition time is 10-15 minutes.

[0039] During the deposition process, the atmosphere consists of argon with 3-7% O₂, creating a mildly reactive atmosphere that promotes the rise of active elements. The operating pressure is 0.4–0.6 Pa, with a total gas flow rate of 10–15 sccm. The target-substrate distance is 120–150 mm to ensure film uniformity. The deposition temperature is controlled between room temperature and 350°C to prevent thermal migration of alloying elements, which could lead to elemental distribution disturbances.

[0040] The resulting high-entropy alloy coating consists of a surface layer, a middle layer, and a bottom layer. The Mn and Cr content in each layer is as follows: surface layer: Mn: 15–25 at.%, Cr <10 at.%, middle layer: Mn: 10–15 at.%, Cr: 10-25 at.%, bottom layer: Mn <10 at.%, Cr >25 at.%. In addition to Mn and Cr, other high-entropy matrix elements such as Fe, Co, Ni, Ti, and Al are also distributed between the coating layers. The total thickness of the high-entropy alloy coating is 30-35 μm, with the middle layer accounting for 60–70% of the total coating thickness.

[0041] (2) Pre-oxidation treatment

[0042] The gradient coating is placed in a heat treatment furnace with controlled oxygen partial pressure for oxidation induction; a tubular or box furnace with the ability to adjust the oxygen partial pressure is used. The temperature setting range is 700–800°C, and the heating rate is controlled at 5°C / min. The oxygen flow rate is 0.4–0.8 sccm, corresponding to an oxygen partial pressure of 10 -4 –10 -3 atm, holding time 40–90 min.

[0043] Through the oxidation induction step, the surface high Mn area can preferentially form MnO2 / Mn2O3, which improves oxygen affinity. The middle layer generates MnCr2O4 spinel and Cr2O3 phase to synergistically inhibit oxygen diffusion. The bottom Cr-rich area further promotes the construction of a dense Cr2O3 skeleton, and finally achieves the external MnO x The film structure is a gradient multiphase synergistic structure consisting of MnCr2O4 in the middle and Cr2O3 in the interior. The slow temperature increase prevents thermal shock and promotes uniform and dense film growth. The resulting film has a dense structure and uniform grains.

[0044] This step can effectively improve the initial quality of the oxide film, reduce oxidation defects and surface active sites, and enhance the stability of the film. Compared with traditional multi-element oxide systems, it has a lower oxidation rate and better interface integrity. The oxidation rate is reduced by more than 70%, and the porosity of the oxide film is less than 0.5%, effectively blocking external oxygen diffusion and interface reactions.

[0045] (3) Surface mechanical strengthening treatment

[0046] After the oxide film is formed, the coating surface is strengthened by any of the following methods: shot peening, laser shock peening, and ultrasonic rolling.

[0047] Shot peening: Use ZrO2 ceramic balls with a particle size of 50–200 μm, a spray speed of 30–100 m / s, and a coverage rate of not less than 100%.

[0048] Laser shock peening: A laser system with a pulse width of 10ns and a single-point energy of 1–5J is used to excite a local plasma shock wave to strengthen the film-substrate bonding interface.

[0049] Surface roughening: Local micro-depression forms a "mechanical locking effect", which enhances the adhesion and peeling resistance between the oxide film and the coating.

[0050] After this treatment step, the adhesion strength and microstructural integrity of the oxide film can be effectively improved, making it less likely to produce failure modes such as peeling and flaking under multiple thermal-mechanical cyclic stresses. Test results show that the bonding strength of the film layer is improved by more than 70%, and the number of thermal shock cycles is increased to more than 1,000 times, which is 2-3 times that of conventional processes.

[0051] In addition, during the oxidation induction stage, the changes in the resistivity of the oxide film can be monitored by a resistance probe to infer the thickness and continuity of the film. The infrared thermal radiation probe can be used to monitor the surface temperature distribution and local heating anomalies of the sample. In situ X-ray photoelectron spectroscopy (XPS) or energy dispersive spectroscopy (EDS) probes can be used to monitor the composition and element valence of the oxide film and analyze the film formation stage and structural evolution. Through the above monitoring modules, the relevant parameters can be adjusted to ensure the quality of the oxide film.

[0052] Specific implementation data are given below to further assist in the explanation.

[0053] Example 1

[0054] In this embodiment, the control goal is to generate a FeCoCrNiMn high-entropy alloy coating on the substrate and form a Mn-Cr composite oxide film, while improving the film-substrate interface bonding strength and avoiding excessive or uneven oxidation. The specific steps are as follows:

[0055] (1) Gradient composition design

[0056] Coating preparation: The thickness of the substrate material is 2 mm. Magnetron sputtering technology is used to deposit the coating in a temperature-controlled vacuum chamber. A mixed gas of Ar+3% O2 ​​is used, the gas pressure is set to 0.4 Pa, the total flow rate is 12 sccm, and the distance between the target and the substrate is set to 140 mm. The deposition process is divided into three stages, each lasting 15 minutes, and the total coating thickness is controlled to be 30 μm. In the bottom stage, the Mn target power is 60 W, and the Cr target power is 150 W; in the middle stage, the Mn target power is 95 W, and the Cr target power is 115 W; in the surface stage, the Mn target power is 130 W, and the Cr target power is 90 W.

[0057] Element sputtering rate adjustment: By controlling the oxygen flow rate of the reaction atmosphere, the sputtering rates of Mn and Cr were controlled within the range of 0.5–1.5 nm / s. The elemental contents of Mn and Cr in each layer are as follows: surface layer: Mn: 21 at.%, Cr: 5 at.%, middle layer: Mn: 13 at.%, Cr: 20 at.%, bottom layer: Mn: 5 at.%, Cr: 45 at.%

[0058] Characterization and analysis: The coating was characterized by electron probe microanalysis (EPMA) and energy dispersive spectroscopy (EDS), confirming that the concentrations of Mn and Cr elements gradually changed along the thickness of the coating.

[0059] (2) Pre-oxidation treatment

[0060] Pre-oxidation treatment process: Place the prepared gradient coating sample in a heat treatment furnace with controllable oxygen partial pressure, and set the oxygen partial pressure in the furnace to 10 -4atm. Set the oxidation temperature to 750°C, with a temperature ramp rate of 5°C / min. The oxidation time was set to 50 minutes. The oxygen flow rate was 0.5 sccm to ensure that the oxygen partial pressure in the oxidation atmosphere remained stable within the set range, preventing atmosphere fluctuations from affecting the quality of the oxide film.

[0061] Oxide film formation: The Mn-rich surface region preferentially forms a Mn2O3 structure, followed by a MnCr2O4 spinel and Cr2O3 phase in the middle layer, and a dense Cr2O3 skeleton in the bottom layer. XRD and TEM confirmed that the composite film was dense and free of pores.

[0062] (3) Surface mechanical strengthening treatment

[0063] Shot peening: ZrO2 ceramic balls with a particle size of 100 μm are used. The spray velocity is 50 m / s, ensuring uniform coarsening of the coating surface microstructure. The spray angle is 45°, and the spray coverage is controlled to 100%. This ensures that the entire surface is evenly shot peened, forming a microscopically rough surface structure.

[0064] Example 2

[0065] In this embodiment, the control goal is to generate an AlCoCrMnTi high-entropy alloy coating on the substrate and form a Mn-Cr composite oxide film, while improving the film-substrate interface bonding strength and avoiding excessive or uneven oxidation. The specific steps are as follows:

[0066] (1) Gradient composition design

[0067] Coating preparation: The thickness of the substrate material is 2 mm. Magnetron sputtering technology is used to deposit the coating in a temperature-controlled vacuum chamber. The deposition pressure is set to 0.5 Pa. By controlling the mixing ratio of argon and oxygen in the atmosphere, the total gas flow rate is ensured to be 12 sccm. Ar+5% O2 mixed gas is used for coating deposition. The distance between the target material and the substrate is set to 120 mm to ensure uniform distribution of elements during the deposition process. The deposition process is divided into three stages, each lasting 15 minutes, and the total coating thickness is controlled to be 35 μm. In the bottom stage, the Mn target power is 70 W, and the Cr target power is 140 W; in the middle stage, the Mn target power is 105 W, and the Cr target power is 125 W; in the surface stage, the Mn target power is 140 W, and the Cr target power is 85 W.

[0068] Element sputtering rate adjustment: By controlling the oxygen flow rate of the reaction atmosphere, the sputtering rates of Mn and Cr were controlled within the range of 0.5–1.5 nm / s. The elemental contents of Mn and Cr in each layer are as follows: surface layer: Mn: 24 at.%, Cr: 7 at.%, middle layer: Mn: 11 at.%, Cr: 15 at.%, bottom layer: Mn: 7 at.%, Cr: 40 at.%

[0069] Characterization and analysis: The coating was characterized by electron probe microanalysis (EPMA) and energy dispersive spectroscopy (EDS), confirming that the concentrations of Mn and Cr elements gradually changed along the thickness of the coating.

[0070] (2) Pre-oxidation treatment

[0071] Pre-oxidation treatment process: Place the prepared gradient coating sample in a heat treatment furnace with controllable oxygen partial pressure, and set the oxygen partial pressure in the furnace to 10 -4 atm. Set the oxidation temperature to 750°C, with a temperature ramp rate of 5°C / min. The oxidation time was set to 60 minutes. The oxygen flow rate was set to 0.6 sccm to ensure that the oxygen partial pressure in the oxidation atmosphere remained stable within the set range, preventing atmosphere fluctuations from affecting the quality of the oxide film.

[0072] Oxide film formation: Highly oxidized phases such as Mn2O3 and Mn3O4 preferentially form in the Mn-rich surface region, followed by MnCr2O4 spinel and Cr2O3 phases in the middle layer, and a dense Cr2O3 skeleton in the bottom layer. XRD and TEM analysis confirmed that the composite film was dense and free of pores.

[0073] (3) Surface mechanical strengthening treatment

[0074] Laser shock peening: The laser pulse width was 8 ns, the single-point energy was set to 4 J, and the pulse repetition rate was 1 Hz. The laser focus was 2.5 mm from the coating surface, and the impact depth was 25 μm. After each impact, a 6-second wait was performed to ensure sufficient heat dissipation and prevent overheating and thermal damage to the coating.

[0075] In summary, the present invention provides a method for preparing a high-entropy alloy coating with high oxidation resistance. Through gradient enrichment design and induced oxidation treatment, it can generate a composite oxide protective film with dense structure and strong thermal stability from the surface to the inner layer of the coating, thereby significantly improving the oxidation resistance and service reliability of the high-entropy alloy coating in high-temperature environments.

[0076] The examples described in the present invention are merely descriptions of the preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy alloy coating with high oxidation resistance, characterized in that: The following steps are involved: (1) Gradient composition design The coating was deposited on the substrate using magnetron sputtering technology. During the preparation process, the Cr target power was gradually reduced and the Mn target power was gradually increased in stages to form a high-entropy alloy coating on the substrate surface. The alloy coating comprises a surface layer, a middle layer and a bottom layer, wherein the element contents of Mn and Cr in each layer are as follows: surface layer: Mn: 15-25 at.%, Cr <10 at.%, middle layer: Mn: 10-15 at.%, Cr: 10-25 at.%, bottom layer: Mn <10 at.%, Cr >25 at.%; (2) Pre-oxidation treatment At a temperature of 700–800°C and an oxygen partial pressure of 10 -4 –10 -3 Oxidation is induced under atm to form an oxide film.

2. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 1, characterized in that: In the step (1), the coating deposition includes three stages: a bottom layer stage: the Cr target power is 140-150W, the Mn target power is 60-70W, and the deposition time is 10-15min; a middle layer stage: the Cr target power is 115-125W, the Mn target power is 95-105W, and the deposition time is 10-15min; and a surface layer stage: the Cr target power is 85-95W, the Mn target power is 130-140W, and the deposition time is 10-15min.

3. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 2, characterized in that: The total thickness of the high entropy alloy coating is 30-35 μm, and the thickness of the middle layer accounts for 60-70% of the total coating thickness.

4. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 1, characterized in that: In the step (1), the coating deposition atmosphere is argon + 3-7% O2.

5. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 4, characterized in that: In the step (1), the working gas pressure for coating deposition is 0.4-0.6 Pa, and the total gas flow rate is 10-15 sccm.

6. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 5, characterized in that: In the step (1), the distance between the target and the substrate is 120-150 mm.

7. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 6, characterized in that: In the step (1), the deposition temperature is controlled between room temperature and 350°C.

8. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 1, characterized in that: In the step (2), the heating rate is controlled at 5°C / min, the oxygen flow rate is 0.4-0.8 sccm, and the holding time is 40-90 min.

9. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 1, characterized in that: The oxide film is a surface MnO x The gradient film structure is formed by the combination of the middle layer MnCr2O4 and the inner layer Cr2O2.

10. The method for preparing a high-entropy alloy coating with high oxidation resistance according to claim 1, characterized in that: The method further includes step (3), wherein after the oxide film is formed, the coating surface is strengthened by any one of shot peening, laser shock strengthening and ultrasonic rolling.

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