Dynamic corrosion properties of impact-fretting wear in high-temperature pure water

Dynamic corrosion is defined as the corrosion that occurs under mechanical actions such as sliding friction, which exposes fresh surfaces and accelerates wear. To estimate the corrosive wear properties of austenitic stainless steel in pure water, impact-fretting wear tests of Type 304 stainless steel disks against Al2O3 balls were performed, and polarization tests were carried out. A scanning electron microscope (SEM), electron-probe micro-analyzer (EPMA), atomic force microscope (AFM), and three-dimensional (3D)-profilometer were used for observation, analysis, and measurement of wear scars. The maximum wear depth of the disk increased with an increase in both water temperature and oxidation time for temperatures below 100 °C. However, the maximum wear depth decreased at 130 °C due to the intact oxide layer adhered to the wear scar of the Type 304 disk. We proposed a wear model for impact-fretting, which showed that dynamic corrosion agreed with the parabolic law of oxidation of metals and the thermal activation process. To specify the process of dynamic corrosion, the activation energy was obtained from the change in the electric current density at different water temperatures using the potential pulse method (PPM) in Na2SO4 solution. The activation energy was approximately the same as that obtained by impact-fretting wear tests in pure water. As a result, the oxide removal efficiency from the fresh surface was less than 10%, and the corrosion of the fresh surface in pure water was caused by electrochemical dissolution according to the micro-cell formation.