Improving Ti-6Al-4V Alloy's Friction And Wear Properties By Complex Processing Technology

Titanium alloys are widely used in aviation industry,medical science,chemical engineering,transportation etc, for their low density, high specific strength,high stability in low and medium temperature,excellent corrosion and bio-compatibility etc.However,the titanium alloys have low hardness,poor wear resistance which limits their more applications. Surface treatment techniques are very effective ways to improve titanium alloy's tribological properties.Conventional surface treatment techniques for titanium alloys just raised titanium alloy's surface hardness,improving wear resistance,such as nitriding carburization boriding and alloying.However, the hardened layer was liable to lose effectiveness and cause microcrack, titanium alloy's wear resistance was increased within a small boundary by single technique.This paper analyzes the properties of titanium alloys and evaluates various surface treatment methods,we proposed composite processing technology.It can enhance the surface hardness,at the meantime possess anti-friction lubricant function。Firstly, nitriding layer was prepared by ion nitriding.Phases of nitriding layer were analyzed by XRD and hardness gradient were tested by micro-hardness tester,the analysis results of nitriding layer show that the surface was constituted by high-hard phase TiN and hardness gradient of diffusion layer declined smooth.Secondly,Mo film was prepared by magnetron sputtering on the surface of nitriding layer.The surface topography was investigated by SEM, The surface element distribution and cross-section element distribution were measurded by EDS,the results show that Mo distributed in the form of graininess on the surface, surface hardness was enhanced,the dense film was well contacted to the body, thickness of the film was about 4μm.Finally,MoS2 possessing quality smooth function was made by sulfur ion technology.Phases of sulfurizing layer were analyzed by XRD and surface topography was investigated by SEM,the results show grain size will gradually enlarge with temperature ingcreasing,especially at 520℃and 620℃. The analysis results of cross-hardness show the surface hardness was the lowest,while the subsurface was the highest and then gradually decreasing,which illustrate the horniness phase can provide enough sustentation to MoS2 on the surface. The analysis results of cross-section element distribution demonstrate the content of S and Mo raised quickly in the first and then decreased sharply,at the same time the content of Ti increased rapidly, next changing within a certain range.The analysis results of friction and wear test show that friction coefficient of sulfurizing at different temperature had obvious variance.It was the best at 220℃.reducing to 0.23. In the same load, friction coefficient of composite layer raised in the first and then stabilized,finally gradually declined,while friction coefficient of nitriding layer increased at last. Under different loads, friction coefficient of composite layer raised with increasing load,when reaching certain load, friction coefficient sharply declined.while friction coefficient of nitriding layer still growed. According wear curve,we learn wear failure of nitriding layer was obviously faster than composite layer.So properties of composite layer were superior to nitriding layer.