Friction and wear behaviour of cp Ti and Ti6Al4V following nitric acid passivation

Nitric acid passivation increases the thickness of the TiO2 passive film formed at the cp Ti and Ti6Al4V surface. The TiO2 oxide, which has a lubricating nature, reduces the wear rate. A linear ball-on-disc friction test has been carried out at room temperature in ambient air, NaCl 3% and Ringer’s solutions, with a sliding velocity of 4 mm s 1 and a normal load of 1 N. Friction coefficient curves obtained from ball-on-disc wear test, as well as following the optical microscopy observation of ball trace, indicated the presence of periodic phenomenon. One period can be divided into four stages. This can be clearly seen for cp Ti (accommodation stage, creation of wear particles, adherence of particles layer on the alumina ball and ejection of this layer). In order to confirm this observation and understand the chemical interfacial phenomena, open circuit potential (OCP) measurements were carried out in the same time of friction tests