Research On Processing And Properties Of Surface Plasma Carbonitriding On Ti6Al4V Alloy

Titanium and titanium alloys are very important structural materials. They have been widelyused in the fields including aerospace industry, chemical industry, recreation and sports commodities,and biomedicine etc, for their outstanding performance in specific strength, high strength in hightemperatures, as well as corrosion resistance and biocompatibility. However, titanium alloys havepoor wear resistance, and are very sensitive to adhesion wear and fretting wear, which prevent themfrom being applied more widely, especially severely limit the uses as frictional components.To solve these problems, a plasma carbonitriding was carried out on the surface of Ti6Al4Valloy using the double glow plasma metallurgy technique. Pure graphite was adopted as the sourcecathode. A hybrid atomosphere of argon and nitrogen with a certain proportion was chosen asworking gas.An orthogonal design test was applied to optimize the best processing parameters of plasmacarbonitriding. The microstructure, composition distribution, phase structure and hardness of theTi(C,N) modified layer were analyzed by OM, SEM/EDS, XRD and nano-indentation tester. Thefriction and wear properties of the modified layer were studied at different speed, load and frictionpair by the ball-on-disc tribometer. Through repeated experiments and explore, the optimumparameters of plasma carbonitriding on T6Al4V alloy are listed as follows: temperature:9050~1050℃, source voltage:900~1000V, cathode voltage:500~600V, distance between sourceelectrode and work-piece:8mm, diffusing time:5h, working pressure:50Pa, flow ratio of Ar/N2:8:1.The Ti(C,N) modified layer is about30μm thick and composed of compound layer and diffusing layer,the contents of C, N and Ti decrease gradually from surface to inner in the modified layer. XRDshows that the major phase of the modified layer is Ti(C0.3N0.7); and the surface hardness is1452HV0.1, about5times compared to that of the Ti6Al4V substrate. Tribological tests show that thefriction coefficients of the modified layer differ little from the substrate, so antifriction effects are notremarkable. However, the volumetric wear rates of the modified layer decrease significantlycomparing to those of the Ti6Al4V, exhibit excellent wear resistant. The polarization curve andelectrochemical impedance spectroscopy in3.5%NaCl solution shows that plasma carbonitridingdoesn’t reduce the corrosion resistance but improves.