Tribological properties of TC4 titanium alloy treated by plasma nitriding at different temperatures

The wear resistance of TC4 titanium alloy was improved by plasma nitriding and the optimum nitriding temperature was investigated. TC4 titanium alloy was nitrided at 650, 700, 750, 800, 850℃ and 900℃ with LDM1-100 plasma nitriding equipment respectively,the temperature holding time is 10 h for each nitriding treatment. The microstructure, surface morphology, surface roughness, phase structure and hardness of nitrided samples at different temperatures were characterized by optical microscope, scanning electron microscope, white light three-dimensional topography instrument and microhardness tester. The tribological properties of TC4 titanium alloy after plasma nitriding were tested by CETR UMT-3 multifunctional friction and wear tester. The results show that the surface microhardness and roughness of TC4 titanium alloy increase with the increase of temperature. After nitriding at 900℃, the surface microhardness of TC4 titanium alloy reaches 1318HV0.05, which is about 4 times as high as that of the substrate (360HV0.05). The increase of hardness is due to the formation of hard nitride phases (TiN and Ti2N phases) on the surface of nitrided sample and the nitride content increases with the increase of nitriding temperature. The load-carrying capacity of nitrided samples at 800℃ and 900℃ is significantly higher than that of nitriding samples at low temperatures (below 750℃). Compared with the original TC4 sample, the wear volume of the nitrided sample significantly reduces. When nitriding temperature is 850℃, the wear volume of the nitrided sample is 1.2% (1 N), 3.0% (3 N) and 62.2% (5 N) of that of the untreated sample, and the improvement of wear resistance of the sample is the most obvious.