Research On Properties Of W-Mo Modified Layer On TC4 Alloy By Double Glow Plasma Alloying Technology

Titanium and its alloys have numerous industrial applications due to their interesting properties, such as light weight, high specific strength, good corrosion resistance and so on. However, insufficient tribological properties and corrosive of non-oxidizing acid solution have always been the major obstacles in the wider application. Surface treatment technique is a feasible solution to these problems, so it has become a research focus in materials science and technology. However, nowadays the surface treatment has been mostly concentrated on a single property. There is high temperature, impact and corrosion etc, apart from friction and wear at the same time in many important application fields. The all-around properties of titanium alloys need to be improved. So it is proposed in this dissertation to fabricate W-Mo modified layer on TC4 alloy to improve high temperature tribological properties, corrosion-wear behaviors and erosion–corrosion properties by double glow plasma alloying technology.W-Mo modified layer was prepared on TC4 substrate by double glow plasma alloying technology. The effects of processing parameters on modified layer were investigated and the optimized parameters were obtained as follows: source voltage:900-1000V; substrate voltage:400-450V; working pressure:35Pa; parallel distance between the source electrode and the substrate:16mm; treatment time:4h. The microstructure, composition and phase structure of the surface modified layers were analyzed by means of SEM, EDS and XRD respectively. Results show that W-Mo modified layer has a thickness of about 23μm. It is consisted of an outer deposition layer and an inner diffusion layer. The adhesive strength between the modified layer and the substrate is well. XRD shows that MoTi, TixW1-x , Mo and W are the major phases of the W-Mo modified layer.It has been systematically studied for the hardness, elastic modulus, high temperature tribological properties, corrosion-wear behaviors and erosion-corrosion properties of W-Mo modified layer. The nano-indentation tests showed that W-Mo modified layers enhanced the surface strength of Ti6Al4V substrate. The average values of hardness and elastic modulus of W-Mo modified layer were 10.86GPa and 278.84 GPa, while substrate was 3.561 GPa and 152 GPa. Ball-on-Disc tests showed that W-Mo modified layer always exhibited lower wear rate compared with Ti6Al4V substrate at 25℃,200℃,450℃. The corrosive-wear behavior of the W-Mo modified layer and TC4 were also studied. In 5wt.%NaCl and 5wt.%H2SO4 solutions, W-Mo modified layer was not significantly decrease coefficient of friction, but enhanced the wear resistance of the titanium alloy. Polarization curves were measured under static state condition and erosion-corrosion in 5wt.%HCl and 5wt.%NaCl solutions by electrochemical tests. Result revealed that W-Mo modified layer corrosion resistance was slightly higher than TC4 substrate.