A method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of K435 high-temperature alloy

Abstract

A method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy belongs to the technical field of titanium alloy nitriding. The invention solves the problem of difficulty in nitriding existing high-temperature alloys with high Ni content. Methods: 1. cold rolling deformation; 2. CrCoAlTi powder supersonic spraying treatment; 3. low-temperature plasma nitriding. The invention is used for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy nitriding. Background Art

[0002] K435 high-temperature alloy is a Ni-based high-temperature alloy independently developed by my country with excellent performance and mature technology. This alloy has been widely used in aviation, aerospace, shipbuilding and other fields. In addition, due to its equiaxed crystal structure, K435 high-temperature alloy has a long service life under high-temperature extreme service conditions and can be used as rotating parts, turbine outer rings, fasteners, etc. However, with the development of society and technology, extreme application conditions urgently require high-temperature alloys to have better service performance, especially hardness and wear resistance.

[0003] Surface modification is one of the common ways to expand the application range of high-temperature alloys. Surface spraying technology is widely used to improve the protective properties of high-temperature alloys. However, traditional thermal spraying processes often bring energy problems such as oxidation and phase change. Therefore, due to its fast and efficient performance, a large number of related studies have been carried out in recent years. Supersonic spraying technology is a material surface modification technology based on aerodynamic principles. It does not rely on thermal energy, but only relies on the speed and kinetic energy of the sprayed powder. A large amount of plastic deformation occurs during the impact process, thereby achieving a tightly bonded coating.

[0004] As we all know, ion nitriding is a surface treatment method that can effectively improve the surface properties of alloys. It has been successfully applied to GH901 and other high-temperature alloys. Low-temperature plasma nitriding can not only provide thermodynamic conditions for the diffusion of nitrogen atoms into the matrix while maintaining the original properties of titanium alloys, but also enable active nitrogen ions to react with the surface of the material to form high-hardness nitrides or nitrogen-containing solid solutions, significantly improving the surface hardness. However, due to the structure of Ni atoms themselves and their tendency to be tightly stacked, nitriding of high-temperature alloys with high Ni content is quite difficult. Summary of the invention

[0005] The present invention aims to solve the problem of difficulty in nitriding existing high-temperature alloys with high Ni content, and provides a method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy.

[0006] A method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy is carried out according to the following steps:

[0007] 1. Cold rolling deformation:

[0008] The high temperature alloy substrate is subjected to cold rolling deformation, the cold deformation degree of which is 10% to 30%, to obtain a deformed substrate;

[0009] 2. CrCoAlTi powder supersonic spraying treatment:

[0010] Under the conditions of supersonic spraying temperature of 600°C to 900°C, nitrogen working intensity of 3MPa to 8MPa and a supersonic spraying gun travel speed of 10mm / s to 1000mm / s, CrCoAlTi powder is supersonic sprayed on the surface of the deformed substrate to obtain a supersonic sprayed substrate;

[0011] 3. Low temperature plasma nitriding:

[0012] In N 2 and H 2 Under the conditions of a mixed atmosphere and a low-temperature plasma nitriding temperature of 500°C to 600°C, the substrate after supersonic spraying is subjected to low-temperature plasma nitriding, thereby completing a method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of the K435 high-temperature alloy.

[0013] The beneficial effects of the present invention are:

[0014] The present invention proposes to use cold deformation to provide N atom diffusion channels and thermodynamic conditions for nitride formation, thereby realizing the formation of a nitrided layer. In addition, supersonic spraying and cold deformation will introduce a large amount of stress on the subsurface and inside of the high-temperature alloy specimen, which will be eliminated during the nitriding process. Finally, cold deformation introduces a deformed structure, and recovery recrystallization will occur during the nitriding process to improve the matrix structure properties. That is, the present invention can modify the surface and matrix of the K435 high-temperature alloy at the same time.

[0015] In order to improve the problems of poor bonding strength, small thickness and high brittleness between the hard coating and the high-temperature alloy substrate, a nitrided layer with a hardness gradient distribution and adjustable layer thickness was prepared on the high-temperature alloy by supersonic spraying and low-temperature plasma nitriding technology. First, the pre-deformed K435 high-temperature alloy was pretreated (grinding, polishing, cleaning, and drying), and then the CrCoAlTi coating was prepared by supersonic spraying. Finally, the supersonic sprayed sample was placed in a low-temperature plasma nitriding furnace for nitriding. During the low-temperature plasma nitriding process, the CrCoAlTi supersonic sprayed layer and N atoms formed a large number of nitrides, including Co-N, Cr-N, Ti-N and Al-N, etc., which have high hardness nitride phases. For example, the hardness of the nitride formed by Ti-N is about 2000HV, the hardness of the nitride formed by Cr-N is about 1500HV, and the hardness of the nitride formed by Al-N is about 1200HV. These nitride phases will further significantly enhance the surface hardness of the sample after supersonic spraying. In addition, the modulus gradient of the coating is related to the service life, and a gentler hardness gradient will be beneficial to the mechanical properties of the specimen, such as wear resistance and fatigue performance. The surface hardness of traditional supersonic spraying is high, and the hardness gradient jitter is serious, which leads to a shortened service life of the coating. In the low-temperature ion nitriding process of the pre-cold-deformed high-temperature alloy specimen, N atoms will complete long-range diffusion along the defect channels such as dislocations generated by cold deformation, and enter the surface of the specimen and deeper below the subsurface. According to the adjustment of the process such as the degree of pre-deformation, nitriding temperature, and nitriding time, a modified layer with high surface hardness and adjustable hardness gradient can be achieved. The method of the present invention can form a nitrided layer with high hardness and a certain hardness gradient distribution on the surface of K435 high-temperature alloy, which can significantly improve the bonding strength between the hardened layer and the high-temperature alloy substrate, improve the wear resistance of the high-temperature alloy, and thereby enhance its service life in extreme environments. The present invention can be used to enhance the surface mechanical properties of parts such as valve bodies and valve covers in valve systems under high-temperature service environments, as well as the surface modification and manufacturing of workpieces that are corrosion-resistant, wear-resistant, and fatigue-resistant at a certain temperature (such as 300°C to 600°C).

[0016] The invention is used for a method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of a method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy according to the present invention;

[0018] Figure 2 The cross-sectional hardness of the composite modified layer K435 high-temperature alloy having high hardness and hardness gradient distribution on the surface of Example 1;

[0019] Figure 3The friction coefficient of the composite modified layer K435 high temperature alloy with high hardness and hardness gradient distribution on the surface of Example 1 is shown. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0021] Specific implementation method 1: Combination Figure 1 Specifically, the method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy described in this embodiment is carried out according to the following steps:

[0022] 1. Cold rolling deformation:

[0023] The high temperature alloy substrate is subjected to cold rolling deformation, the cold deformation degree of which is 10% to 30%, to obtain a deformed substrate;

[0024] 2. CrCoAlTi powder supersonic spraying treatment:

[0025] Under the conditions of supersonic spraying temperature of 600°C to 900°C, nitrogen working intensity of 3MPa to 8MPa and a supersonic spraying gun travel speed of 10mm / s to 1000mm / s, CrCoAlTi powder is supersonic sprayed on the surface of the deformed substrate to obtain a supersonic sprayed substrate;

[0026] 3. Low temperature plasma nitriding:

[0027] In N 2 and H 2 Under the conditions of a mixed atmosphere and a low-temperature plasma nitriding temperature of 500°C to 600°C, the substrate after supersonic spraying is subjected to low-temperature plasma nitriding, thereby completing a method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of the K435 high-temperature alloy.

[0028] This embodiment provides a method for preparing a composite modified layer with a hardness gradient distribution on the surface of a K435 high-temperature alloy based on supersonic spraying of CrCoAlTi. The method of this embodiment can form a composite modified layer with a hardness gradient distribution on the surface of a K435 high-temperature alloy, which can significantly improve the bonding strength between the modified layer and the K435 high-temperature alloy substrate, improve the toughness and wear resistance of the modified layer, and expand its application range. The surface hardness and hardness distribution of the composite modified layer can be regulated by the temperature, pressure, number of CrCoAlTi coating layers deposited by supersonic spraying, and the temperature and time of low-temperature plasma nitriding.

[0029] The main components of the composite modified coating are Cr, Co, Al, and Ti, and the whole contains N. The specific structure of the composite modified layer is a nitrogen-containing high-temperature alloy substrate and a nitrogen-containing CrCoAlTi layer. The composite modified layer with high surface hardness and adjustable certain hardness gradient distribution is obtained after cold rolling deformation, supersonic spraying and plasma nitriding.

[0030] The processing method of the protective coating with high hardness and gentle and adjustable hardness gradient on the surface of the high-temperature alloy of this embodiment is as follows: first, the substrate is not ground and polished to remove the oxide scale to avoid the problem of oxide scale cracking in the subsequent cold rolling experiment; then the high-temperature alloy substrate is subjected to cold rolling deformation treatment by using cold rolling equipment to provide a favorable channel for the diffusion of N atoms in the subsequent nitriding; then, at least one to multiple layers of CrCoAlTi primer coating are supersonic sprayed on the substrate surface using nitrogen as a carrier gas by a supersonic spraying spray gun, and the multi-layer CrCoAlTi coating can increase the final coating thickness to meet the service requirements of long-term wear; finally, the high-temperature alloy deformed substrate with CrCoAlTi coating is nitrided by ion nitriding to complete the preparation of the composite modified layer, and high-hardness nitrides with Cr, Co, Ti, and Al-N nitrides are formed on the surface, and the deformed substrate forms a Ni solid solution containing N with a gradient distribution of the N element during the nitriding process. These formed phase structures lead to a special modified layer structure with high surface hardness and a certain hardness gradient distribution. In addition, due to the gentle hardness gradient of the coating, the bonding force between it and the substrate is greatly enhanced, and the wear resistance and fatigue life will be greatly enhanced, meeting the special service requirements in actual application processes.

[0031] In this embodiment, supersonic spraying is performed on the cold-deformed high-temperature alloy. Preferably, the deformation amount of the cold deformation process is 10% to 30%. A lower deformation amount can provide sufficient defects inside the high-temperature alloy to achieve long-range diffusion of N atoms during nitriding (crystal defects such as dislocations can increase diffusion channels) and the formation of surface nitrides (crystal defects can provide thermodynamic conditions for nitrides).

[0032] The supersonic spraying temperature of this embodiment is 600°C to 900°C, the working strength of the nitrogen is 3MPa to 8MPa, the particle size distribution range of the CrCoAlTi alloy powder is 10μm to 80μm, and the speed range of the supersonic spraying gun is 10mm / s to 1000mm / s. The CrCoAlTi coating prepared by spraying has a small thermal effect on the substrate, a high deposition rate, a low coating porosity, and a high bonding strength. At the same time, pressure is a determining factor in whether the powder particles can reach a critical speed (when the speed is greater than this speed, the particles collide and deposit on the substrate surface to form a coating, and when the particle speed is less than this critical speed, erosion will occur), so a gas pressure of 3MPa to 8MPa is selected; a higher spraying temperature can further increase the speed of the powder particles, and the increase in gas temperature will also allow the powder particles to obtain a certain temperature, which will help to more easily produce plastic flow deformation when impacting the substrate, so the selected supersonic spraying temperature is 600°C to 900°C; the nitrogen pressure and temperature specified in this embodiment cause the spraying speed to reach 2 to 3 times the speed of sound; since the gas has a relatively small density and viscosity coefficient, the gas has limited force on the powder particles, so the powder particles cannot be too large; if the particles are too small, they will be affected by the high-speed airflow on the substrate surface to generate shock waves, so the particle size distribution range of the selected CrCoAlTi alloy powder is 10μm to 80μm.

[0033] In this embodiment, a pre-deformed K435 high-temperature alloy with a CrCoAlTi coating on its surface is subjected to low-temperature plasma nitriding. The low-temperature plasma nitriding temperature is preferably 500°C to 600°C. The low-temperature plasma nitriding is carried out at a flow rate ratio of 1:3. 2 and H 2 In this embodiment, the low-temperature plasma nitriding time is selected according to the required composite modified layer thickness and hardness. Generally, the longer the nitriding time, the thicker the nitriding layer, the more high-hardness stable nitrides, the greater the thickness and hardness of the nitriding layer, and the hardness gradient will tend to be gentle. At the same time, due to the plastic deformation of the substrate during the cold rolling process, the stress accumulated in the substrate during the low-temperature nitriding process will be released (especially, supersonic spraying will further affect the surface of the sample, forming dislocation rings around the sprayed particles, dislocation plugging), and the matrix structure will recrystallize during the nitriding process. In addition, the defect channel will provide long-range diffusion of N atoms during the nitriding process, and the hardness gradient will tend to be gentle. Therefore, the performance of the high-temperature alloy matrix structure will be improved synchronously. Therefore, the simultaneous enhancement of the surface and the matrix makes the hardness of the matrix from the surface to the core present a gradient distribution, the overall hardness increases, and the overall nitriding layer thickness increases. Thereby, while improving the problems of poor bonding, small thickness, and poor toughness between the hardened layer and the high-temperature alloy matrix, a nitriding layer with high surface hardness and hardness gradient distribution is obtained.

[0034] The beneficial effects of this embodiment are:

[0035] This embodiment proposes to use cold deformation to provide N atom diffusion channels and thermodynamic conditions for nitride formation, so as to achieve the formation of a nitrided layer. In addition, supersonic spraying and cold deformation will introduce a large amount of stress on the subsurface and inside of the high-temperature alloy specimen, which will be eliminated during the nitriding process. Finally, cold deformation introduces a deformed structure, and recovery recrystallization will occur during the nitriding process to improve the matrix structure properties. That is, this embodiment can modify the surface and matrix of the K435 high-temperature alloy at the same time.

[0036] In order to improve the problems of poor bonding strength, small thickness and high brittleness between the hard coating and the high-temperature alloy substrate, a nitrided layer with a hardness gradient distribution and adjustable layer thickness was prepared on the high-temperature alloy by supersonic spraying and low-temperature plasma nitriding technology. First, the pre-deformed K435 high-temperature alloy was pretreated (grinding, polishing, cleaning, and drying), and then the CrCoAlTi coating was prepared by supersonic spraying. Finally, the supersonic sprayed sample was placed in a low-temperature plasma nitriding furnace for nitriding. During the low-temperature plasma nitriding process, the CrCoAlTi supersonic sprayed layer and N atoms formed a large number of nitrides, including Co-N, Cr-N, Ti-N and Al-N, etc., which have high hardness nitride phases. For example, the hardness of the nitride formed by Ti-N is about 2000HV, the hardness of the nitride formed by Cr-N is about 1500HV, and the hardness of the nitride formed by Al-N is about 1200HV. These nitride phases will further significantly enhance the surface hardness of the sample after supersonic spraying. In addition, the modulus gradient of the coating is related to the service life, and a gentler hardness gradient will be beneficial to the mechanical properties of the specimen, such as wear resistance and fatigue performance. The surface hardness of traditional supersonic spraying is high, and the hardness gradient jitter is serious, which leads to a shortened service life of the coating. In the process of low-temperature ion nitriding of the high-temperature alloy specimen that has been cold-deformed in advance, N atoms will complete long-range diffusion along the defect channels such as dislocations generated by cold deformation, and enter the surface of the specimen and deeper below the subsurface. According to the adjustment of the process such as the degree of pre-deformation, nitriding temperature, and nitriding time, a modified layer with high surface hardness and adjustable hardness gradient can be achieved. The method of this embodiment can form a nitrided layer with high hardness and a certain hardness gradient distribution on the surface of K435 high-temperature alloy, which can significantly improve the bonding strength between the hardened layer and the high-temperature alloy substrate, improve the wear resistance of the high-temperature alloy, and thereby enhance its service life in extreme environments. This embodiment can be used to enhance the surface mechanical properties of parts such as valve bodies and valve covers in valve systems under high-temperature service environments, as well as the surface modification and manufacturing of workpieces that are corrosion-resistant, wear-resistant, and fatigue-resistant at a certain temperature (such as 300°C to 600°C).

[0037] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the high temperature alloy substrate described in step 1 is a high temperature alloy substrate after cutting and removing the oxide scale. The rest is the same as specific implementation method 1.

[0038] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that: in step 1, the deformed substrate is ground, polished, cleaned and dried. The rest is the same as specific implementation method 1 or 2.

[0039] Specific embodiment 4: This embodiment is different from specific embodiments 1 to 3 in that the high temperature alloy substrate described in step 1 is a K435 high temperature alloy substrate. The rest is the same as specific embodiments 1 to 3.

[0040] Specific embodiment 5: This embodiment is different from specific embodiments 1 to 4 in that the particle size of the CrCoAlTi powder in step 2 is 10 μm to 80 μm. The rest is the same as specific embodiments 1 to 4.

[0041] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that the molar ratio of Cr, Co, Al and Ti in the CrCoAlTi powder in step 2 is 1:1:1:1. The rest is the same as specific embodiments 1 to 5.

[0042] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the spraying speed in step 2 is 2 to 3 times the speed of sound. The rest is the same as specific embodiments 1 to 6.

[0043] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that: in step 2, CrCoAlTi powder is supersonic sprayed onto the deformed substrate surface in one or more layers. The rest is the same as specific embodiments 1 to 7.

[0044] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that in step 3, the substrate after supersonic spraying is subjected to low-temperature plasma nitriding for 15 hours to 60 hours. The rest is the same as specific embodiments 1 to 8.

[0045] Specific implementation method 10: This implementation method is different from the specific implementation methods 1 to 9 in that: the N 2 and H 2 In the mixed atmosphere of N 2 With H 2 The volume ratio is 1:3. Other aspects are the same as those of the first to ninth embodiments.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Embodiment 1:

[0048] A method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high-temperature alloy is carried out according to the following steps:

[0049] 1. Cold rolling deformation:

[0050] The high temperature alloy substrate is subjected to cold rolling deformation, the cold deformation degree is 10%, and a deformed substrate is obtained;

[0051] 2. CrCoAlTi powder supersonic spraying treatment:

[0052] Under the conditions of supersonic spraying temperature of 600°C, nitrogen working intensity of 3MPa and supersonic spraying gun travel speed of 200mm / s, CrCoAlTi powder was supersonic sprayed on the deformed substrate surface for 10 layers to obtain a supersonic sprayed substrate;

[0053] 3. Low temperature plasma nitriding:

[0054] In the vacuum plasma nitriding furnace chamber, N 2 and H 2 Under the conditions of a mixed atmosphere and a low-temperature plasma nitriding temperature of 550°C, the substrate after supersonic spraying was subjected to low-temperature plasma nitriding for 15 hours to obtain a composite modified layer K435 high-temperature alloy with high hardness and hardness gradient distribution on the surface.

[0055] The high-temperature alloy substrate described in step 1 is a high-temperature alloy substrate that has been cut and the oxide scale has been removed using 80# water sandpaper.

[0056] In step 1, the deformed substrate is ground, polished, cleaned and dried. Specifically, the deformed substrate surface is ground with 400#, 600#, 800#, 1500# and 2000# water sandpaper to remove the surface oxide film, and then ultrasonically cleaned in distilled water for 15 minutes, polished with diamond polishing agent spray, polished to a mirror surface, and then ultrasonically cleaned in acetone, alcohol and distilled water for 30 minutes respectively to remove oil and residual polishing agent on the surface of the sample, and finally dried with cold air from a hair dryer and placed on the substrate table of the supersonic spraying equipment.

[0057] The high temperature alloy substrate described in step 1 is a K435 high temperature alloy substrate.

[0058] The average particle size of the CrCoAlTi powder in step 2 is 25 μm.

[0059] In step 2, the molar ratio of Cr, Co, Al and Ti in the CrCoAlTi powder is 1:1:1:1.

[0060] The CrCoAlTi powder in step 2 is dried CrCoAlTi powder, specifically placed in a vacuum drying oven and dried at 100° C. for 1 hour.

[0061] The spraying speed in step 2 is 2 to 3 times the speed of sound.

[0062] In step 2, the substrate after supersonic spraying is cleaned and dried.

[0063] N in step 3 2 and H 2 In the mixed atmosphere of N 2 With H 2 The volume ratio is 1:3.

[0064] Embodiment 2: This embodiment is different from Embodiment 1 in that the degree of cold deformation in step 1 is 30%. Other aspects are the same as Embodiment 1.

[0065] Embodiment 3: This embodiment is different from Embodiment 1 in that the supersonic spraying temperature in step 2 is 800° C. The rest is the same as Embodiment 1.

[0066] Embodiment 4: This embodiment is different from Embodiment 1 in that the nitrogen working intensity in step 2 is 5 MPa. The rest is the same as Embodiment 1.

[0067] Embodiment 5: This embodiment is different from Embodiment 1 in that the average particle size of the CrCoAlTi powder in step 2 is 50 μm. The rest is the same as Embodiment 1.

[0068] Embodiment 6: This embodiment is different from the embodiment 1 in that the speed of the supersonic spraying gun in step 2 is 400 mm / s. The rest is the same as the embodiment 1.

[0069] Embodiment 7: This embodiment is different from Embodiment 1 in that the low-temperature plasma nitriding temperature in step 3 is 600° C. The rest is the same as Embodiment 1.

[0070] Embodiment 8: This embodiment differs from Embodiment 1 in that in step 3, the substrate after supersonic spraying is subjected to low-temperature plasma nitriding for 25 hours. The rest is the same as Embodiment 1.

[0071] Figure 2 The cross-sectional hardness of the composite modified layer K435 high temperature alloy with high hardness and hardness gradient distribution on the surface of Example 1. As can be seen from the figure, the surface of the K435 high temperature alloy has a nitrided layer with high hardness and a certain hardness gradient distribution.

[0072] Figure 3 The friction coefficient of the composite modified layer K435 high temperature alloy with high hardness and hardness gradient distribution on the surface of Example 1 is shown in the figure. As can be seen from the figure, the friction coefficient in the stable wear stage is about 0.3.

[0073] According to the ASTM C1624-05 standard test, the bonding strength of the composite modified layer with high hardness and hardness gradient distribution on the surface of the K435 high temperature alloy in Example 1 is 130 MPa.

Claims

1. A method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of K435 high temperature alloy, characterized in that The preparation method is carried out according to the following steps:

1. Cold rolling deformation: The high temperature alloy substrate is subjected to cold rolling deformation, the cold deformation degree is 10%, and a deformed substrate is obtained; 2. CrCoAlTi powder supersonic spraying treatment: Under the conditions of supersonic spraying temperature of 600°C to 900°C, nitrogen working intensity of 3MPa to 8MPa and a supersonic spraying gun travel speed of 10mm / s to 1000mm / s, CrCoAlTi powder is supersonic sprayed on the surface of the deformed substrate to obtain a supersonic sprayed substrate; The particle size of the CrCoAlTi powder is 10 μm to 80 μm; the molar ratio of Cr, Co, Al and Ti in the CrCoAlTi powder is 1:1:1:1; the spraying speed is 2 to 3 times the speed of sound; 3. Low temperature plasma nitriding: Under the conditions of a mixed atmosphere of N2 and H2 and a low-temperature plasma nitriding temperature of 550°C, the substrate after supersonic spraying was subjected to low-temperature plasma nitriding for 15 hours, thus completing the preparation of a composite modified layer with high hardness and hardness gradient distribution on the surface of the K435 high-temperature alloy; The volume ratio of N2 to H2 in the mixed atmosphere of N2 and H2 is 1:

3.

2. The method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high temperature alloy according to claim 1, characterized in that The high-temperature alloy substrate described in step 1 is a high-temperature alloy substrate after cutting and removing oxide scale.

3. The method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high temperature alloy according to claim 1, characterized in that In step one, the deformed substrate is ground, polished, cleaned and dried.

4. The method for preparing a composite modified layer with high hardness and hardness gradient distribution on the surface of a K435 high temperature alloy according to claim 1, characterized in that Step 2: Supersonic spraying CrCoAlTi powder onto the deformed substrate surface in one layer or more.

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