Proposed method to examine the effect of cycling temperatures on friction illustrated with intermetallic Ni-Sn coatings sliding against corundum

A methodology is proposed to examine the tribological behavior of materials subjected to successive ascents and descents in temperature. The experimental approach is based on performing two types of high temperature reciprocating sliding tests and subsequently correlating the evolution of the coefficient of friction of the tribosystem with test temperature. In the first series, the sliding tests are conducted at increasing temperatures with the aim to identify the temperature regions where changes in friction might occur. These changes can be either due to a surface modification (e.g. a change in the oxidation and/or wear mechanism) or structural one (e.g. phase transformation). In the second series, tests are performed under isothermal conditions selected based on the outcome of the elevated temperature results, with the aim to evaluate the influence of oxidation on the frictional behavior of the thermally stable system. As a case study, electroplated intermetallic Ni-Sn coatings containing either 16 or 64 wt% Sn of interest on jet engine bearings, were investigated. These coatings were tested between 25 and 400 °C in ambient air relevant for that application.