Effects of Scratching Rate on the Corrosion Wear Mechanism of Ti-6Al-4V Alloys

Abstract

Titanium and its alloys are currently in use as implant materials for orthopaedic surgery. These alloys own outstanding corrosion resistance due to a dense and passive oxide film of a few nanometers' thickness on their surfaces. When these alloys are implanted in a living body, implanted surface material removal takes place because of mechanical wear and corrosion. Material degradation, due to simultaneous chemical and mechanical effects, limits long-term use of metallic biomaterials, such as stainless steels and titanium alloys. Thus, it is very important to investigate synergistic interaction between wear and corrosion. 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, first, we developed a new tribocorrosion system and then we estimated corrosion wear characteristics of the alloys with special attention focused on the effects scratching rate on repassivation behavior. Two types of corrosion wear tests were carried out. One was a free corrosion potential measurement with simultaneous application of wear damage and the other was potentiostatic polarization testing with wear damage. To discuss the corrosion wear mechanism, the damaged surfaces were carefully observed by a scanning electron microscope. It was concluded that in corrosion wear environment, a transition of wear type from abrasive to adhesive was observed with an increase in the scratching rates. A higher scratching rate prevented regeneration of passive films on worn surfaces, resulting in the generation of relatively large corrosion pits and changes in wear form. These results suggested that the scratching rate was an important factor that affected the damage accumulation process.