Method for improving surface hardness of titanium alloy

Abstract

The invention discloses a method for improving the surface hardness of a titanium alloy. The method comprises the following steps: 1, cleaning the surface of the titanium alloy; secondly, B4C powder is poured into a rosin binder to form reinforced phase paste, the cleaned titanium alloy surface is smeared with the reinforced phase paste, and a reinforced phase prefabricated layer is formed; thirdly, plasma arc cladding is conducted on the reinforced phase prefabricated layer, and a hardened layer containing TiC and TiB reinforced phases is formed on the surface of the titanium alloy; and 4, mechanically polishing the hardened layer. According to the method, plasma arc smelting is adopted, so that a titanium alloy matrix and B4C powder particles are subjected to an in-situ reaction in a molten pool, a stable and dispersively distributed in-situ authigenic TiC and TiB reinforced phase hardened layer is formed, the surface hardness and wear resistance of the titanium alloy are remarkably improved, meanwhile, the binding force of the hardened layer and the titanium alloy matrix is improved, and the service life of the titanium alloy is prolonged. The material can be applied to end connectors of tank chains, acetabular bones in biomedical treatment, aero-engine hydraulic actuating cylinders and other parts needing hardness and wear resistance improvement.

Description

Technical Field

[0001] The invention relates to the technical field of metal material surface modification, and in particular to a method for improving the surface hardness of a titanium alloy. Background Art

[0002] Titanium and titanium alloys are used in aviation, aerospace, ships, weapons, petroleum, chemical industry, medical and other fields due to their advantages of low density, high specific strength and corrosion resistance. However, due to the disadvantages of low hardness, poor wear resistance, large and unstable friction coefficient, the scope of application of titanium alloys is greatly limited. The hardness of pure titanium is about 15~20HRC, and the hardness of titanium alloys is generally lower than 35HRC. In view of the shortcomings of low hardness and poor wear resistance of titanium alloys, a variety of surface modification technologies for titanium alloys have been developed. Early research mainly included traditional surface technologies such as electroplating, thermal diffusion, thermal oxidation, PVD, and CVD. In recent years, with the continuous emergence of new technologies, modern surface technologies such as micro-arc oxidation, plasma spraying, supersonic spraying, ion implantation, electron beam deposition, laser nitriding, ion diffusion, and new technologies combining multiple surface technologies and film structure design have been applied to the research of titanium alloy surface modification. These technologies have achieved remarkable results in improving the friction and wear properties of titanium alloys, but there are still common shortcomings such as thin coating layer, poor impact resistance, and weak bonding with the matrix material. Therefore, it is necessary to develop surface modification technology to prepare titanium alloy surfaces with high hardness and good bonding with the matrix.

[0003] Plasma arc cladding technology melts the surface of the base material by cladding the additional material, so that the base surface and the additional material melt, and achieves metallurgical bonding between the cladding layer and the base. The structure and performance of the cladding layer can be controlled by adjusting the cladding process. Compared with other process technologies, plasma arc cladding has the following characteristics and advantages: 1. The plasma arc heating method has fewer restrictions on materials, a wider range of material selection, and easier cladding of carbides and oxides; 2. The molten state is maintained for a long time, with high energy utilization, which is conducive to uniform solidification structure composition and better exhaust slag; 3. The coating clad by plasma arc is metallurgically bonded to the base with high bonding strength. In summary, the use of plasma arc cladding technology to clad the reinforcing phase on the surface of titanium alloy can further improve the surface hardness of titanium alloy. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the surface hardness of titanium alloy in view of the shortcomings of the above-mentioned prior art. The method adopts plasma arc melting to make the titanium alloy matrix and B4C powder particles react in situ in the molten pool to form a hardened layer of stable and dispersed in-situ self-generated TiC and TiB reinforcement phases, which significantly improves the surface hardness and wear resistance of the titanium alloy, and at the same time improves the bonding strength between the hardened layer and the titanium alloy matrix, solving the current problem of low surface hardness of titanium alloy and weak bonding between the coating and the matrix material.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for improving the surface hardness of titanium alloy, characterized in that a prefabricated layer of a reinforcing phase on the surface of a titanium alloy substrate is melted by a plasma arc cladding method, so that the reinforcing phase precursor powder reacts with the titanium alloy substrate in situ to obtain a hardened layer of an in-situ generated reinforcing phase; the method comprises the following steps: Step 1: Clean the surface of titanium alloy; Step 2: Pour B4C powder into rosin binder and stir to form reinforcing phase paste, then evenly apply the reinforcing phase paste to the surface of the titanium alloy cleaned in step 1 to form a reinforcing phase prefabricated layer; Step 3: Place the titanium alloy with the reinforcement phase prefabricated layer in step 2 in a closed cabin containing a plasma gun, and continuously introduce argon gas into the cabin, and then perform plasma arc cladding. Set the cladding path so that the plasma arc gun head moves perpendicularly to the titanium alloy and melts the B4C powder in the reinforcement phase prefabricated layer, forming a hardened layer containing TiC and TiB reinforcement phases on the surface of the titanium alloy; Step 4: Mechanically polish the hardened layer formed on the surface of the titanium alloy in step 3 until the surface roughness meets the use requirements.

[0006] The above-mentioned method for improving the surface hardness of titanium alloy is characterized in that the cleaning process described in step one is: first use acid to remove the oxide film on the surface of the titanium alloy, and then use acetone to clean and remove the oil and residual liquid on the surface of the titanium alloy; at the same time, the plasma arc equipment is debugged to the set process parameters, and the air tightness, oxygen content and water content of the cabin are checked.

[0007] The above method for improving the surface hardness of titanium alloy is characterized in that in step 2, B4C powder and rosin binder are placed in a mortar in a mass ratio of 1:1 for mixing and stirring to form a reinforcing phase paste. The reinforcing phase paste prepared in this mass ratio has good viscosity.

[0008] The above-mentioned method for improving the surface hardness of titanium alloy is characterized in that the particle size range of the B4C powder in step 2 is 1.5μm~3.0μm.

[0009] The above-mentioned method for improving the surface hardness of titanium alloy is characterized in that the process parameters of the plasma arc cladding in step three include: plasma arc power of 2500W~3000W, scanning speed of 1500mm / min~2000mm / min, and overlap rate of 50%.

[0010] The above method for improving the surface hardness of titanium alloy is characterized in that the plasma arc cladding in step 3 is performed in an argon atmosphere. By performing plasma arc cladding in an argon atmosphere, high-temperature oxidation of the titanium alloy during the cladding process is avoided, thereby ensuring the quality of the hardened layer.

[0011] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts a plasma arc melting method to melt B4C powder on the surface of titanium alloy, so that the titanium alloy matrix and B4C powder particles react in situ in the molten pool to form a hardened layer of stable, dispersed in-situ self-generated TiC and TiB reinforcing phases. These reinforcing phases have the characteristics of small size, thermodynamic stability, no interface pollution, high bonding strength with the matrix, etc., which significantly improves the surface hardness and wear resistance of the titanium alloy, and at the same time improves the bonding strength between the hardened layer and the titanium alloy matrix.

[0012] 2. The in-situ self-generated TiC and TiB reinforcing phases contained in the hardened layer prepared by the present invention have a thermal expansion coefficient close to that of the titanium alloy substrate, which reduces the stress and cracking tendency of the cladding hardened layer, ensures that the cladding hardened layer and the substrate have a good match in thermal physical properties, enables the substrate surface and the cladding hardened layer to achieve metallurgical bonding, and further improves the bonding strength between the hardened layer and the titanium alloy substrate.

[0013] 3. The present invention adjusts the content of B4C powder in the reinforcing phase prefabricated layer to control the content of the reinforcing phase in the hardened layer, combines the control of the composition of the cladding object and the optimization of the cladding process to jointly adjust the surface hardness performance of the titanium alloy, which can usually be adjusted between 40HRC and 65HRC; at the same time, by controlling the number of cladding layers and the number of overlaps, the area and thickness of the hardened layer formed by cladding are adjusted to meet different surface hardness requirements.

[0014] 4. The method of the present invention is applicable to titanium and titanium alloy materials, and the cladding raw materials can use SiC and TiC powder particles in addition to B4C powder. The corresponding reinforcement phases generated may include TiC, TiB, Ti5Si3, etc. and undissolved particles. It has a wide range of applications and is suitable for promotion.

[0015] 5. The hardened layer formed on the surface of the titanium alloy in the present invention has excellent hardness and wear resistance, and can be widely used in end connectors of tank chains, acetabulum bones in biomedicine, hydraulic actuators of aircraft engines and other parts that need to improve hardness and wear resistance.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a schematic diagram of the process for improving the surface hardness of titanium alloy according to the present invention.

[0018] Figure 2 This is a cross-sectional morphology diagram of the hardened layer formed on the surface of the titanium alloy in Example 1 of the present invention.

[0019] Figure 3This is a microstructure morphology diagram of the hardened layer formed on the surface of the titanium alloy in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] Example 1 like Figure 1 As shown, this embodiment includes the following steps: Step 1: First, use acid to remove the oxide film on the surface of TC4 titanium alloy, and then use acetone to clean and remove the oil and residual liquid on the surface of TC4 titanium alloy. At the same time, debug the plasma arc equipment to the set process parameters, and check the air tightness, oxygen content and water content of the cabin; Step 2: Place B4C powder with a particle size range of 1.5 μm to 3.0 μm and rosin binder in a mortar at a mass ratio of 1:1 and stir and mix them evenly with a glass rod to form a reinforcing phase paste, and then evenly apply the reinforcing phase paste to the surface of the TC4 titanium alloy cleaned in step 1 to form a reinforcing phase prefabricated layer with a thickness of about 1 mm; Step 3: placing the TC4 titanium alloy with the reinforcement phase prefabricated layer in step 2 in a closed cabin containing a plasma gun, and continuously introducing argon gas into the cabin, and then performing plasma arc cladding in an argon atmosphere, setting a cladding path so that the plasma arc gun head moves perpendicularly to the TC4 titanium alloy and melts the B4C powder in the reinforcement phase prefabricated layer, and forming a hardened layer containing TiC and TiB reinforcement phases on the surface of the TC4 titanium alloy; the process parameters of the plasma arc cladding include: a plasma arc power of 2500W, a scanning speed of 1500mm / min, and an overlap rate of 50%; Step 4: Mechanically polish the hardened layer formed on the surface of the TC4 titanium alloy in step 3 until the surface roughness meets the use requirements.

[0021] Figure 2 is a cross-sectional morphology diagram of the hardened layer formed on the surface of the titanium alloy in this embodiment. Figure 2 It can be seen that the thickness of the hardness layer is about 200 μm.

[0022] Figure 3 is the microstructure of the hardened layer formed on the surface of the titanium alloy in this embodiment. Figure 3 It can be seen that there are granular TiC and rod-shaped TiB reinforcement phases in the hardened layer.

[0023] Example 2 like Figure 1 As shown, this embodiment includes the following steps: Step 1: First, use acid to remove the oxide film on the surface of TC4 titanium alloy, and then use acetone to clean and remove the oil and residual liquid on the surface of TC4 titanium alloy. At the same time, debug the plasma arc equipment to the set process parameters, and check the air tightness, oxygen content and water content of the cabin; Step 2: Place B4C powder with a particle size range of 1.5 μm to 3.0 μm and rosin binder in a mortar at a mass ratio of 1:1 and stir and mix them evenly with a glass rod to form a reinforcing phase paste, and then evenly apply the reinforcing phase paste to the surface of the TC4 titanium alloy cleaned in step 1 to form a reinforcing phase prefabricated layer with a thickness of about 1 mm; Step 3: placing the TC4 titanium alloy with the reinforcement phase prefabricated layer in step 2 in a closed cabin containing a plasma gun, and continuously introducing argon gas into the cabin, and then performing plasma arc cladding in an argon atmosphere, setting a cladding path so that the plasma arc gun head moves perpendicularly to the TC4 titanium alloy and melts the B4C powder in the reinforcement phase prefabricated layer, and forming a hardened layer containing TiC and TiB reinforcement phases on the surface of the TC4 titanium alloy; the process parameters of the plasma arc cladding include: a plasma arc power of 2800 W, a scanning speed of 1800 mm / min, and an overlap rate of 50%; Step 4: Mechanically polish the hardened layer formed on the surface of the TC4 titanium alloy in step 3 until the surface roughness meets the use requirements.

[0024] Example 3 like Figure 1 As shown, this embodiment includes the following steps: Step 1: First, use acid to remove the oxide film on the surface of TC4 titanium alloy, and then use acetone to clean and remove the oil and residual liquid on the surface of TC4 titanium alloy. At the same time, debug the plasma arc equipment to the set process parameters, and check the air tightness, oxygen content and water content of the cabin; Step 2: Place B4C powder with a particle size range of 1.5 μm to 3.0 μm and rosin binder in a mortar at a mass ratio of 5:20 and stir and mix evenly with a glass rod to form a reinforcing phase paste, and then evenly apply the reinforcing phase paste to the surface of the TC4 titanium alloy cleaned in step 1 to form a reinforcing phase prefabricated layer with a thickness of about 1 mm; Step 3, placing the TC4 titanium alloy with the reinforcement phase prefabricated layer in step 2 in a closed cabin containing a plasma gun, and continuously introducing argon gas into the cabin, and then performing plasma arc cladding in an argon atmosphere, setting a cladding path so that the plasma arc gun head moves perpendicularly to the TC4 titanium alloy and melts the B4C powder in the reinforcement phase prefabricated layer, and forming a hardened layer containing TiC and TiB reinforcement phases on the surface of the TC4 titanium alloy; the process parameters of the plasma arc cladding include: a plasma arc power of 3000W, a scanning speed of 2000mm / min, and an overlap rate of 50%; Step 4: Mechanically polish the hardened layer formed on the surface of the TC4 titanium alloy in step 3 until the surface roughness meets the use requirements.

[0025] In summary, the present invention discloses a method for improving the surface hardness of titanium alloys, wherein a reinforcing phase paste is prefabricated on a titanium alloy substrate, and then a plasma arc is used for cladding, and TiC and TiB reinforcing phases are generated by in-situ reaction in the molten pool. The reinforcing phase is very close to the thermal expansion coefficient of the titanium alloy substrate, which reduces the stress and cracking tendency of the cladding layer, ensures that the cladding layer and the substrate have a good thermophysical property match, and realizes metallurgical bonding between the substrate surface and the cladding layer. The hardened layer prepared by the method of the present invention has good hardness and wear resistance, and can be widely used in end connectors of tank chains, acetabular bones in biomedicine, hydraulic actuators of aircraft engines, and other parts that need to improve hardness and wear resistance.

[0026] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for improving the surface hardness of a titanium alloy, characterized in that: The plasma arc cladding method is used to melt the reinforcement phase prefabricated layer on the surface of the titanium alloy substrate, so that the reinforcement phase precursor powder reacts with the titanium alloy substrate in situ to obtain a hardened layer with an in-situ generated reinforcement phase; the method comprises the following steps: Step 1: Clean the surface of titanium alloy; Step 2: Pour B4C powder into rosin binder and stir to form reinforcing phase paste, then evenly apply the reinforcing phase paste to the surface of the titanium alloy cleaned in step 1 to form a reinforcing phase prefabricated layer; Step 3: Place the titanium alloy with the reinforcement phase prefabricated layer in step 2 in a closed cabin containing a plasma gun, and continuously introduce argon gas into the cabin, and then perform plasma arc cladding. Set the cladding path so that the plasma arc gun head moves perpendicularly to the titanium alloy and melts the B4C powder in the reinforcement phase prefabricated layer, forming a hardened layer containing TiC and TiB reinforcement phases on the surface of the titanium alloy; Step 4: Mechanically polish the hardened layer formed on the surface of the titanium alloy in step 3 until the surface roughness meets the use requirements.

2. A method for improving the surface hardness of titanium alloy according to claim 1, characterized in that: The cleaning process described in step one is: first use acid to remove the oxide film on the surface of the titanium alloy, and then use acetone to clean and remove the oil and residual liquid on the surface of the titanium alloy; at the same time, debug the plasma arc equipment to the set process parameters, and check the air tightness, oxygen content and water content of the cabin.

3. A method for improving the surface hardness of titanium alloy according to claim 1, characterized in that: In step 2, the B4C powder and the rosin binder are placed in a mortar in a mass ratio of 1:1 and mixed and stirred to form a reinforcing phase paste.

4. The method for improving the surface hardness of titanium alloy according to claim 1, characterized in that: The particle size range of the B4C powder in step 2 is 1.5 μm to 3.0 μm.

5. The method for improving the surface hardness of titanium alloy according to claim 1, characterized in that: The process parameters of the plasma arc cladding in step three include: plasma arc power of 2500W~3000W, scanning speed of 1500mm / min~2000mm / min, and overlap rate of 50%.

6. The method for improving the surface hardness of titanium alloy according to claim 1, characterized in that: The plasma arc cladding described in step 3 is performed in an argon atmosphere.

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