In order to improve the surface properties, the TC4 titanium alloy was subjected to low-pressure vacuum nitriding treatment at different temperatures. Scanning electron microscope and X-ray diffraction were used to analyze the structure of the nitrided layer, and the microhardness and wear resistance of the nitrided layer were tested. The results show that after the low-pressure vacuum nitriding treatment of the TC4 titanium alloy, a modified layer composed of the surface layer TiN and the subsurface layer Ti2AlN can be obtained. When the temperature is low, the amount of nitride formed on the surface is small, the infiltration layer is thin, and the hardness is low. As the temperature increases, the number of nitrides increases, the thickness of the infiltration layer increases, and the hardness and wear resistance also increase. When the temperature reaches 820 ℃, the surface hardness can reach 1000 ～ 1100 HV, and the depth of the hardened layer is 50 -60 μm. As the temperature continues to increase, the nitride aggregates grow up, the nitrided layer begins to become loose, and the hardness and wear resistance decrease.
Titanium and its alloys have become the most attractive materials in the field of aerospace and biomedicine due to their excellent physical, chemical and mechanical properties, especially high corrosion resistance, specific strength and good biocompatibility. Used in various other fields. However, due to the shortcomings of poor fatigue resistance, hardness, wear resistance and fretting wear resistance of such materials, their application is limited. Titanium nitride has the advantages of high hardness, low friction coefficient, excellent chemical stability, good biocompatibility and electrical conductivity, and is widely used in machinery, electronics, medicine, decoration and other fields. Zhao Bin et al. Used a quartz tube furnace to nitrify the titanium alloy with ammonia gas. The wear resistance was nearly twice that of the non-nitrided sample, but the depth of the hardened layer was only a few microns, and the treatment time was up to 50 h. Zhao et al. Treated the Ti-6Al-4V alloy with plasma spraying to form TiN in situ, which significantly improved the wear resistance of the titanium alloy. However, the surface of the coating is rough after spraying, because spraying speed is high, spraying is not easy to control. Guo Aihong et al. Used magnetron sputtering to prepare TiN coating on the surface of titanium alloy, which greatly improved the wear resistance of titanium alloy. However, after magnetron sputtering, there was an obvious interface between the film and the substrate, and the bonding strength was poor. The coating is thin, and many performance indicators are not ideal. Jiang et al. Used a laser treatment method to prepare a TiN coating on the surface of a titanium alloy, resulting in a modified layer with high hardness, high wear resistance, and a certain thickness. However, when laser nitriding, a large thermal stress is generated in the cladding layer, which is easy to produce crack. Because nitrogen and titanium have a strong affinity, and titanium alloys are easy to oxidize, the preparation of nitrided layers on the surface of titanium alloys has a thin hardened layer, high brittleness, poor bonding strength with the substrate, uneven coating and processing time Too long and other issues. Therefore, how to obtain a nitride modified layer with high hardness, high wear resistance, good stability, and high bonding strength with the matrix is still a difficult problem and a focus of current research.
After the TC4 titanium alloy was treated by vacuum nitriding at different temperatures and low pressures, a nitride modified layer composed of TiN and Ti2AlN was formed on the surface layer. The number of nitrides, the thickness of the nitrided layer, the hardness and the wear resistance increase with increasing temperature. When the temperature reaches 820 ° C, the nitrided layer is dense and combines well with the substrate. The surface hardness can reach 1000 ～ 1100 HV. The depth of the hardened layer It is 50 ~ 60 μm, and the hardness gradient is gentle. As the temperature continues to increase, the nitride aggregates grow up, the nitrided layer begins to become loose, and the hardness and wear resistance decrease.