The corrosion/wear mechanisms of Ti-6Al-4V alloy for different scratching rates

Titanium and its alloys are currently in use as implant materials for orthopaedic surgery. These materials possess outstanding corrosion resistance due to a dense and passive oxide film on the surface. When these alloys are implanted in a living body, removal of surface material takes place because of mechanical wear and corrosion. Simultaneous chemical and mechanical effects also limit long-term use of such materials. The aim of the present study is to clarify the damage accumulation mechanism of Ti-6Al-4V alloys under the simultaneous reaction of corrosion and wear. For this purpose, we developed a new tribocorrosion system and then evaluated corrosion wear characteristics of the alloys with special attention focused on the effects of scratching rate on repassivation behavior. Two types of corrosion wear tests were carried out: one was the free corrosion potential measurement and the other was the potentiostatic polarization test both with simultaneous application of wear damage. In corrosion wear environment, a transition of wear type from abrasive to adhesive was observed with increase of the scratching rates. Higher scratching rate prevented regeneration of passive films on worn surfaces, resulting in generation of relatively large corrosion pits and a change in the wear mechanism. These results suggested that the scratching rate was an important factor affecting the damage accumulation process.