Tribological Behaviors Of Ti6Al4V With Surface Plasma Molybdenized

Titanium alloys, such as Ti6Al4V, are widely used in the fields including aerospace, bioengineering, mechanical engineering and sports equipment due to their outstanding performance in specific strength, high temperature resistance, corrosion resistance and biocompatibility. However, titanium alloys suffer from the serious disadvantages of poor tribological properties, which prevent them from being applied more widely. To solve these problems, this paper proposed to form the molybdenizing modification layer on Ti6Al4V alloys by double glow plasma surface metallurgy technique. At the same time, it must ensure that there is no significantly change in the microstructure and tensile property and that the loss rate of mechanical properties should not exceed 10% after the surface plasma molybdenizing treatment.The optimum parameters of surface plasma molybdenizing technique were carried out by orthogonal experiment design. The microstructure, composition distribution, phase structure and hardness of the molybdenizing modification layer were analyzed by OM, SEM/EDS, XRD and nano-indentation tester. The friction and wear properties of the molybdenizing modified layer were studied at different temperatures, load, speed and different friction pair by the ball-on-disc tribometer. Through analyzing the orthogonal experiment results, the optimum processing parameters of plasma molybdenizing on T6Al4V alloy are listed as follows: temperature: 900~950℃, source voltage: 900~950V, cathode voltage: 400~450V, distance between source electrode and work-piece: 15mm, working pressure: 30~35Pa, diffusing time: 3h. The molybdenizing modified layer is about 27μm thick and composed of Mo-deposited layer and Mo-diffusing layer. XRD shows that (Ti,Al8,Mo,V)and AlTi2 are the major phases of the Mo-diffusing layer. The hardness and elastic modulus of the molybdenizing modified layer are 13.832GPa and 804.27GPa, which are 4 and 5 times larger than those of the Ti6Al4V substrate, respectively. Pin-on-Disc tests show that the volumetric wear rates of the molybdenizing modified layer decreased significantly compared to those of the Ti6Al4V bare metal under different conditions. The tensile test shows that the tensile strength of the surface plasma molybdenizing sample decreased slightly about 2.97% compared to that of the substrate, and the molybdenizing modified layer have no cracks or peelings at the fracture surface.