The effect of surface topography on tribo-oxidation of titanium nitrided surfaces

Abstract

Two different methods of surface treatments which employ different mechanisms to produce titanium nitrided surfaces were utilized in this study, namely plasma nitriding of titanium substrate and TiN PVD coating. The surface roughness of the plasma nitrided titanium samples has been found to decrease to a minimum and then increase with increasing temperature. TiN ion plating caused little change to the surface topography, which is generally smoother than plasma nitrided surfaces. Dry sliding and rolling-sliding wear test results were used to evaluate the tribo-oxidation properties of the plasma nitrided and TiN ion plated titanium surfaces in contact with an alumina ball or a similar disc. The present study with regard to oxidative wear has shown that the usefulness of the protective layer on the titanium surface depends mainly on the roughness of the surface. Because of the absence of lubrication it was to be expected that surface finish and the interlocking of asperities would have a greater effect than under lubricated conditions. What was surprising, however, was to find that increasing surface roughness had the opposite effect in the two types of dry test conducted. When a coated surface was rubbed against an alumina ball, the smoothest surface was worn most. However, when the same coated surface in rolling-sliding tests rubbed against another disc with the same coating, the roughest surface was worn most. Nevertheless, none of the coatings tested can be considered resistant to wear without lubrication.