A method for preparing a titanium alloy grid-shaped gradient surface modification layer

Abstract

The application discloses a preparation method of a titanium alloy grid-shaped gradient surface modification layer, and the specific process of the method is as follows: sequentially performing surface pretreatment, high-energy shot peening, grid coating pretreatment and ion nitriding treatment on the titanium alloy to form the grid-shaped gradient surface modification layer on the surface of the titanium alloy. The high-energy shot peening forms a refining layer on the surface of the titanium alloy, reduces ion nitriding resistance, improves the nucleation rate of N-containing compounds, thereby improving the thickness of the surface modification layer and enhancing the wear resistance of the surface modification layer, simultaneously forming a gradient transition of surface layer hardness, improving the bonding force between the nitriding layer and the titanium alloy substrate, and forming a grid surface nitriding layer through the grid coating pretreatment, improving the wear resistance of the modification layer, thereby obtaining a special double-structure composite surface modification layer with the grid-shaped surface nitriding layer and the longitudinal hardness gradient distribution on the surface of the titanium alloy, so that the titanium alloy modification layer has the performances of high hardness, good wear resistance and not easy to fall off, and is suitable for titanium alloy structural parts.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of titanium alloy, and particularly relates to a preparation method of a titanium alloy grid-shaped gradient surface modification layer. BACKGROUND

[0002] Titanium alloy has low density, high specific strength, good mechanical properties and corrosion resistance, and has been more and more widely used in recent years. However, titanium alloy has poor wear resistance and is very sensitive to adhesive wear and fretting fatigue damage. These characteristics greatly reduce the safety and reliability of titanium alloy components. Therefore, the research on surface strengthening modification treatment of titanium alloy has become a research focus. The existing technologies include anodic treatment, chemical nickel plating, ion implantation, plasma nitriding, laser nitriding, laser alloying, electron beam nitriding, diamond coating, plasma spraying, physical vapor deposition, etc. However, there is a common problem that the thickness of the surface modification layer or coating is relatively thin, and only has a wear-reducing effect at low load, while at high load, high speed and high temperature, the coating often cracks or even peels off due to stress or thermal stress, resulting in failure.

[0003] Many improvements have been made to the coating thickness and bonding force through composite surface modification technology. CN101444149A discloses a method for generating a functional gradient composite surface layer on a metal by using a thermal plasma. The method can make the plasma flow rapidly warm up to near the melting point on the surface of the substrate, and the high-energy ionized gas atoms react with the substrate to form a compound layer with good bonding force on the surface of the substrate. CN103643243A discloses a high strength and toughness surface modification method for metal materials. The method processes the substrate by laser shot peening and magnetic field nitriding to obtain a composite surface modification layer with small surface grain size, deep nitriding layer and good strength and toughness. CN112323013A discloses a method for preparing a high film-substrate bonding force composite coating on the surface of a titanium alloy. The method prepares a nitriding layer by high-energy shot peening and ion nitriding process, and finally deposits a composite surface strengthening layer on the surface to form a composite modification layer composed of a 15μm-100μm thick nanocrystalline ion nitriding layer and a 3μm-8μm thick PVD hard film layer. CN112410722A discloses an α+β type titanium alloy based on cold forming composite low-temperature nitriding treatment and a method for forming a nitriding layer of the titanium alloy. The method obtains more dislocation defects by quenching and cold forming deformation treatment, and then combines low-temperature nitriding treatment and thermal diffusion treatment to obtain an ultra-thick nitriding layer with a thickness greater than 1mm. CN106480399A discloses a method for preparing a gradient nanostructure nitriding layer on the surface of a titanium alloy. The method repeatedly processes the surface of the titanium alloy by ultrasonic deep rolling nanocrystallization, and then combines a glow ion nitriding treatment process to prepare a gradient nanostructure nitriding layer, thereby enhancing the corrosion resistance, wear resistance and fatigue resistance of the material surface. The existing surface treatment methods have their own advantages, but all have the characteristic that the thickness, hardness and bonding force of the nitriding layer are difficult to be compatible. SUMMARY

[0004] The technical problem solved by the present application is to provide a preparation method of a titanium alloy grid-shaped gradient surface modification layer to solve the problems of the prior art. The method combines high-energy shot peening with grid coating pretreatment and ion nitriding. The high-energy shot peening forms a refined layer on the surface of the titanium alloy, reduces the ion nitriding resistance, and improves the nucleation rate of N-containing compounds, thereby increasing the thickness of the surface modification layer and enhancing its wear resistance. Meanwhile, the method forms a gradient transition of the surface layer hardness, improves the bonding force between the nitriding layer and the titanium alloy substrate, and forms a grid-shaped surface nitriding layer through grid coating pretreatment. Due to the advantages of the grid-shaped structure, the surface residual stress formed during the nitriding process is small, which reduces the problems of easy peeling caused by high hardness, high brittleness, and large residual stress of the nitriding layer, and further improves the wear resistance of the modification layer. The method solves the problem that the thickness, hardness, and bonding force of the nitriding layer are difficult to be compatible in the prior art.

[0005] To solve the above technical problems, the technical solution adopted by the present application is a preparation method of a titanium alloy grid-shaped gradient surface modification layer, characterized in that the specific process of the method is as follows: sequentially performing surface pretreatment, high-energy shot peening, grid coating pretreatment, and ion nitriding treatment on the titanium alloy to form a grid-shaped gradient surface modification layer on the surface of the titanium alloy.

[0006] The preparation method of the titanium alloy grid-shaped gradient surface modification layer, characterized in that the surface pretreatment process is as follows: polishing the surface of the titanium alloy and then cleaning it with ethanol, and the surface roughness of the titanium alloy after the surface pretreatment is less than 1.6 μm. The above surface pretreatment reduces the surface roughness of the titanium alloy, providing a basic guarantee for obtaining a relatively flat shot peening deformation layer through subsequent high-energy shot peening.

[0007] The preparation method of the titanium alloy grid-shaped gradient surface modification layer, characterized in that the pressure of the high-energy shot peening is 0.4 MPa to 0.6 MPa, and the shot peening time is 15 min to 30 min. The process parameters of the high-energy shot peening are controlled to obtain the optimal matching of the shot peening deformation layer depth and surface flatness.

[0008] The preparation method of the titanium alloy grid-shaped gradient surface modification layer, characterized in that the projectile used in the high-energy shot peening is a cast steel shot with a diameter of 0.3 mm, the shot peening speed is 40 m / s, and the coverage rate is 200%. The relatively small diameter of the projectile compared with conventional shot peening particles ensures the flatness of the deformed surface as much as possible.

[0009] The preparation method of the titanium alloy grid-shaped gradient surface modification layer has the characteristics that the process of the grid coating pretreatment is: after high-energy shot peening, a 1200 DEG C-resistant organic silicon coating is coated on the titanium alloy surface to form a grid-shaped high-temperature-resistant coating, and after drying, the coating process is repeated 2-3 times until the coating is uniform, and then the titanium alloy is placed in an electric heating treatment furnace and heated at 250 DEG C for 10 hours, and after taking out, the titanium alloy is air-cooled. The grid-shaped high-temperature-resistant coating with a certain thickness and uniformity is formed by repeated coating, which ensures the subsequent nitriding effect and is beneficial to obtain a uniform nitriding layer.

[0010] The preparation method of the titanium alloy grid-shaped gradient surface modification layer has the characteristics that the process of the grid coating pretreatment is: after high-energy shot peening, a 1200 DEG C-resistant organic silicon coating is coated on the titanium alloy surface to form a grid-shaped high-temperature-resistant coating, and after drying, the coating process is repeated 2-3 times until the coating is uniform, and then the titanium alloy is placed in an electric heating treatment furnace and heated at 250 DEG C for 10 hours, and after taking out, the titanium alloy is air-cooled. The grid-shaped high-temperature-resistant coating with a certain thickness and uniformity is formed by repeated coating, which ensures the subsequent nitriding effect and is beneficial to obtain a uniform nitriding layer.

[0011] The preparation method of the titanium alloy grid-shaped gradient surface modification layer has the characteristics that the process of the grid coating pretreatment is: after high-energy shot peening, a 1200 DEG C-resistant organic silicon coating is coated on the titanium alloy surface to form a grid-shaped high-temperature-resistant coating, and after drying, the coating process is repeated 2-3 times until the coating is uniform, and then the titanium alloy is placed in an electric heating treatment furnace and heated at 250 DEG C for 10 hours, and after taking out, the titanium alloy is air-cooled. The grid-shaped high-temperature-resistant coating with a certain thickness and uniformity is formed by repeated coating, which ensures the subsequent nitriding effect and is beneficial to obtain a uniform nitriding layer.

[0012] Compared with the prior art, the present application has the following advantages:

[0013] 1. The present application forms a grain gradient refinement layer on the surface of the titanium alloy substrate by high-energy shot peening, generates a large number of grain boundaries and other structural defects, and effectively reduces the kinetic resistance of subsequent ion nitriding with the increase of lattice distortion and defect density, thereby easily forming a high-concentration N atom aggregation on the surface of the titanium alloy, greatly improving the nucleation rate of N-containing compounds, and further improving the nitriding depth and the wear resistance of the surface modification layer. At the same time, the nanometer refinement layer formed by high-energy shot peening improves the hardness of the shallow surface layer of the titanium alloy substrate, thereby forming a gradient transition of the surface layer hardness after subsequent ion nitriding treatment, so that the surface hardening layer has a gradient hardness structure feature in the depth direction, greatly improves the bonding force between the surface modification layer and the titanium alloy substrate, and reduces the risk of coating peeling caused by large hardness difference between the substrate and the coating.

[0014] 2. Nitrided layers have high strength but also high brittleness and residual stress. Under high loads or high friction speeds, due to the inherent hard and brittle nature of the TiN compounds contained in the nitrided layer, thicker nitride layers are more susceptible to cracking. Once cracks initiate, they tend to propagate along grain boundaries, leading to damage or spalling of the compound layer. To address this, this invention employs a mesh coating pretreatment combined with subsequent ion nitriding to form a mesh-like surface nitrided layer. Utilizing its structural advantages, it reduces residual stress during the nitriding process, resulting in a surface nitrided layer with better fracture resistance than workpieces treated with conventional nitriding. Simultaneously, the mesh-like surface modification layer retains part of the substrate surface, preserving the advantages of the titanium alloy substrate, thus offering superior application prospects in areas such as fatigue fracture resistance.

[0015] 3. Compared with traditional ion nitriding treatment, the mesh-like gradient surface modification layer prepared by this invention on the titanium alloy surface is uniform, not easy to peel off, has good corrosion resistance, and has superior surface hardness and wear resistance. At the same time, because the mesh-like high-temperature resistant coating isolates some H atom diffusion channels, less H atoms diffuse into the titanium alloy matrix, thus maintaining the high performance level of the titanium alloy matrix. It will not cause hydrogen embrittlement of the titanium alloy due to the large introduction of H atoms during the nitriding process, so that the plasticity of the titanium alloy remains at a high level.

[0016] 4. This invention uses high-energy shot peening combined with grid nitriding process to prepare a special dual-structure composite surface modification layer with a grid-like surface nitriding layer and a longitudinal hardness gradient distribution. It realizes the depth and surface bidirectional structural design of the titanium alloy nitriding layer and can be extended to other titanium alloy structural surface treatment fields.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a photograph of the TC4 titanium alloy plate with a mesh-like gradient surface modification layer prepared in Example 1 of the present invention. Detailed Implementation

[0019] Example 1

[0020] This embodiment includes the following steps:

[0021] Step 1: Surface pretreatment of TC4 titanium alloy sheet: After polishing the surface of TC4 titanium alloy sheet, it is cleaned with ethanol, and the surface roughness of TC4 titanium alloy sheet after surface pretreatment is less than 1.6μm.

[0022] Step two, the TC4 titanium alloy plate after surface pretreatment in step one is subjected to high-energy shot peening treatment: the pressure of high-energy shot peening is 0.6 MPa, the shot peening time is 30 min, the shot is cast steel shot with a diameter of 0.3 mm, the shot peening speed is 40 m / s, and the coverage rate is 200%;

[0023] Step three, the TC4 titanium alloy plate after high-energy shot peening treatment in step two is subjected to grid coating pretreatment: the surface of the TC4 titanium alloy plate after high-energy shot peening is subjected to polishing treatment, the surface of the TC4 titanium alloy plate after high-energy shot peening is polished to be smooth and flat by using 2000 mesh sandpaper, and a grid paper is covered on the polished surface, then a 1200℃-resistant organic silicon coating is brushed on the grid paper to form a grid-shaped high-temperature-resistant coating, after drying, the coating process is repeated twice until the coating is uniform, and then the TC4 titanium alloy plate is placed in an electric heating treatment furnace and heated at 250℃ for 10 h, and then taken out and air-cooled; the grid paper has a designed size of the hollow grid;

[0024] Step four, the TC4 titanium alloy plate after grid coating pretreatment in step three is subjected to ion nitriding treatment: the ion nitriding treatment adopts a glow plasma nitriding process, and the equipment used is an ion nitriding furnace, the voltage is 400 V, the vacuum degree is not higher than 0.1 Pa, the nitriding gas is composed of nitrogen and argon with a flow ratio of 1:1, the nitriding gas flow rate is 5 L / min, the nitriding temperature is 720℃, and the time is 12 h, so as to form a grid-shaped gradient surface modification layer on the surface of the TC4 titanium alloy plate, as shown in Figure 1

[0025] After detection, the surface hardness of the grid-shaped gradient surface modification layer prepared in this embodiment is 982 HV; the wear loss of the surface strengthening layer is 1.1 mg under the conditions of a load of 100 N, a rotating speed of 100 r / min, a time of 20 min, and a Great Wall lubricating oil medium; after the modification treatment, the tensile strength of the TC4 titanium alloy plate substrate is 951 MPa, the yield strength is 899 MPa, and the elongation is 17.5%.

[0026] Example 2

[0027] This embodiment includes the following steps:

[0028] Step one, the TC29 titanium alloy plate is subjected to surface pretreatment: after polishing the surface of the TC29 titanium alloy plate, the surface is cleaned by using ethanol, and the surface roughness of the TC29 titanium alloy plate after surface pretreatment is less than 1.6 μm;

[0029] Step two, the TC29 titanium alloy plate after surface pretreatment in step one is subjected to high-energy shot peening treatment: the pressure of high-energy shot peening is 0.4 MPa, the shot peening time is 15 min, the shot is cast steel shot with a diameter of 0.3 mm, the shot peening speed is 40 m / s, and the coverage rate is 200%; ​

[0030] Step three, the TC29 titanium alloy plate after high-energy shot peening in step two is subjected to grid coating pretreatment: the surface of the TC29 titanium alloy plate after high-energy shot peening is subjected to polishing treatment, the surface of the TC29 titanium alloy plate after high-energy shot peening is polished to be smooth and flat by using 2000-mesh sandpaper, and a grid paper is covered on the polished surface, then a 1200℃-resistant silicone coating is brushed on the grid paper to form a grid-shaped high-temperature-resistant coating, after drying, the coating process is repeated for 3 times until the coating is uniform, and then the TC29 titanium alloy plate is placed in an electric heating treatment furnace and heated at 250℃ for 10h, and then taken out and air-cooled; the grid paper has a designed size of the hollow grid;

[0031] Step four, the TC29 titanium alloy plate after grid coating pretreatment in step three is subjected to ion nitriding treatment: the ion nitriding treatment adopts a glow plasma nitriding process, and an ion nitriding furnace is used as the equipment, the voltage is 600V, the vacuum degree is not higher than 0.1Pa, the nitriding gas is composed of nitrogen and argon with a flow ratio of 1:1, the nitriding gas flow rate is 10L / min, the nitriding temperature is 800℃, and the time is 20h, and a grid-shaped gradient surface modification layer is formed on the surface of the TC29 titanium alloy plate.

[0032] It is detected that the surface hardness of the grid-shaped gradient surface modification layer prepared in the embodiment is 998HV; the wear loss weight of the surface strengthening layer is 3.2mg under the conditions of a load of 100N, a rotating speed of 100r / min, a time of 20min, and a longcheng lubricating oil medium; after the modification treatment, the tensile strength of the TC29 titanium alloy plate substrate is 1052MPa, the yield strength is 984MPa, and the elongation is 10%.

[0033] The above is only a preferred embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent change made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A method for producing a titanium alloy grid-shaped gradient surface modification layer, characterized by, The method comprises the following steps: surface pretreatment, high-energy shot peening, grid coating pretreatment and ion nitriding treatment of the titanium alloy in sequence to form a grid-shaped gradient surface modification layer on the surface of the titanium alloy; the grid coating pretreatment process comprises the following steps: coating a 1200 DEG C-resistant silicone coating on the surface of the titanium alloy after high-energy shot peening to form a grid-shaped high-temperature-resistant coating, repeating the coating process 2-3 times until the coating is uniform, and then placing the titanium alloy in an electric heating treatment furnace and heating at 250 DEG C for 10 hours, and then taking out and air cooling.

2. The method for preparing a titanium alloy mesh-like gradient surface modification layer according to claim 1, characterized in that, The surface pretreatment process comprises the following steps: polishing the surface of the titanium alloy and then cleaning the polished surface with ethanol, and the surface roughness of the titanium alloy after the surface pretreatment is less than 1.6 microns.

3. The method for preparing a titanium alloy mesh-like gradient surface modification layer according to claim 1, characterized in that, The high-energy shot peening pressure is 0.4-0.6 MPa, and the shot peening time is 15-30 minutes.

4. The method for preparing a titanium alloy mesh-like gradient surface modification layer according to claim 3, characterized in that, The shot used in the high-energy shot peening is cast steel shot with a diameter of 0.3 mm, the shot peening speed is 40 m / s, and the coverage rate is 200%.

5. The method for preparing a titanium alloy mesh-like gradient surface modification layer according to claim 1, characterized in that, Before the coating, the surface of the titanium alloy after the high-energy shot peening is polished, the surface of the titanium alloy after the high-energy shot peening is polished to be smooth and flat with 2000-mesh sandpaper, and a grid paper is covered on the polished surface; the grid paper has a designed size of the hollow grid.

6. The method for preparing a titanium alloy mesh-like gradient surface modification layer according to claim 1, characterized in that, The ion nitriding treatment adopts a glow plasma nitriding process, and the equipment used is an ion nitriding furnace, the voltage is 400-600 V, the vacuum degree is not higher than 0.1 Pa, the nitriding gas is composed of nitrogen and argon with a flow ratio of 1:1, the nitriding gas flow rate is 5-10 L / min, the nitriding temperature is 600-800 DEG C, and the time is 12-20 hours.

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