Wear and Corrosion Resistance of Titanium Alloy with Cobalt Based Alloying Layer

Cobalt-based alloy layer was prepared on Ti6Al4V alloy substrate using double glow plasma alloying technology in order to improve the wear and corrosive resistance of substrate. Then the coated titanium alloy was treated by shot-peening to improve its thermal damage of fatigue resistance during high temperature processing. The microstructure, constituent distribution, hardness and toughness of the coating were studied by scanning electron microscopy(SEM), X-ray diffraction(XRD), glow-discharge photo-electron spectroscopy, micro-hardness tester, static indentation tester and dynamic repeating press equipment, respectively. The influence of cobalt-based alloy coating as well as post-treatment on the wear behavior and corrosion resistance of Ti alloy substrate in ambient air and 3.5% NaCl aqueous solution (mass fraction) was evaluated by ball-on-disk tribometer and electrochemical tests. The results indicated that the cobalt-based alloy layer consisted of deposition layer of 20 μm and diffusion layer of 5 μm. Composition elements were distributed along the gradient layer. Surface hardness of alloyed layer was HK_0.98N 718. The wear resistance of Ti alloy substrate with Co-based alloying layer increased by 28 times, which was attributed to the improvement of substrate surface hardness nearly by 2 times by the coating and good lubrication and friction reduction properties of the coating. Furthermore, the coated surface showed obvious passivation features and had better corrosion resistance than that of Ti alloy substrate. After shot-peening post-treatment by ceramic balls at intensity of 0.15 mm A (Almen intensity), the thickness of top deposition layer of Co-based alloy coating was thinned by 1/5, surface hardness increased slightly and hardness gradient in alloying layer became slow down to a certain degree, while surface toughness was enhanced obviously. But the shot-peening post-treatment not only led to reduction of surface wear resistance with the wear rate of combined treatment surface being 1/10 of titanium alloy, but also resulted in the weakening of anti-electrochemical corrosion property of alloy layer compared to that of titanium alloy substrate.