The influence of atmospheric composition on the abrasive wear of titanium and Ti-6Al-4V

Abstract

A pin-on-disc apparatus has been used to investigate the wear and friction (sliding force) behaviour of metals on bonded silicon carbide and alumina papers under conditions of controlled atmospheric composition. The wear rates of both commercial-purity titanium and the alloy Ti-6%Al-4%V tested in air were found to remain constant with time, in contrast with the behaviour of other metals tested under similar conditions, which exhibited a progressive decrease in wear rate with increasing number of passes along the same track. In an atmosphere of dry inert gas (argon or nitrogen), the wear record for titanium and Ti-6Al-4V divided into two linear sections. In the first period, the wear rate was slightly higher in nitrogen and slightly lower in argon than that observed in dry air, while in the second it was substantially lower in both inert gases than in air. The influence of argon in reducing the wear rate was significantly greater than that of nitrogen. In an atmosphere of pure oxygen, an increase of about 30% was observed over the wear rate in dry air. It is proposed that the concentration of interstitial nitrogen and oxygen in the worn metal surface, which largely determines its mechanical properties, strongly influences both the ductility of the abraded material and the force of adhesion between the metal and the abrasive particles. Parallels are drawn between abrasive wear and machining to illustrate the importance of oxygen at the interface between workpiece and tool surfaces.