<i>In-situ</i> Observation of Sliding Interface in Commercially Pure Titanium Sheet with a TiO<sub>2</sub> Film

To investigate the factor that cause the variation in friction coefficient by sliding conditions in commercially pure titanium coated titanium oxide film, in-situ observation of sliding interface during ball on block test and EBSD analysis of a sliding cross-section were performed. At the vertical load of 0.1 N, the friction coefficient stabilized at a low level of approximately 0.12. However, at 0.5 N, the friction coefficient varying widely in the range of 0.20–0.80. At 2.0 and 4.0 N, the friction coefficient stabilized at a high level, approximately 0.30 and 0.40, respectively. At the vertical load of 0.5 N, the friction coefficient was negatively correlated to the Taylor factor for the uniaxial compression of the titanium grains directly beneath the film. Thus, it can be presumed that the ploughing term of friction coefficient increased due to the enhancement of compressive strain of titanium. On the other hands, at vertical loads of 2.0 and 4.0 N, the ball is always in contact with multiple grains due to the larger contact area. As a result, it is considered that the influence of Taylor factor was equalized and the variation of friction coefficient got smaller.