Double glow plasma surface Cr-Ni alloying of Ti6Al4V alloys: Mechanical properties and impact of preparing process on the substrate

Surface Cr-Ni alloying of Ti6Al4V alloys was achieved by double-glow plasma surface metallurgy technology. The adhesion strength and nano-indentation hardness of Ti-CrNi alloy coatings with 20, 40, 60, and 80 at% Ni contents were investigated respectively. Effects of process on the metallographic structure, tensile strength and fatigue resistance of Ti6Al4V alloys were analyzed in detail. The results show that Ti-CrNi alloy coatings were dense, uniform, and compact, including a complete structure of deposited layer, interdiffusion layer, and sputtering-affected zone. With increasing of Ni, the adhesion of the deposited layer raised. However, the nano-hardness of the deposition layer gradually declines. The addition of Ni does not have significant impact on the nano-hardness of interdiffusion layer. Plasma alloying treatment resulted in the α-phase grain size of Ti6Al4V increased and a “net structure” appeared. After plasma alloying, the tensile strength of Ti6Al4V was about 2.1% higher than the solid solution annealing state. However, the fatigue life of Ti6Al4V after plasma alloying process declined.