Coefficient of friction evolution with temperature under fretting wear for FeCrAl fuel cladding candidate

Abstract A leading cause of fuel failures in U.S. pressurized water reactor power plants is grid-to-rod fretting. One of the major variables affecting fretting wear is the coefficient of friction (COF). Reliability of the fuel cladding is influenced by the COF and thus it is important to know how the material's COF will be affected by temperature transients. Kanthal advanced powder metallurgy technology or APMT, a FeCrAl steel alloy, is being investigated as a commercial alternative to conventional fuel cladding in a nuclear reactor due to its potentially favorable performance under accident conditions. This leaves APMT steel fretting performance to be examined. Tests were performed to examine the evolution of the COF with temperature under fretting. The contact was simulated with both a cylindrical and a rectangular specimen over a line contact area. Confocal scanning laser microscopy was used to obtain a 3D map of the surface, which was used to calculate the wear rate coefficient of the samples. The wear rate coefficient was compared to wear volume to show the effects of the COF and temperature on wear. Energy Dispersive Spectroscopy was performed to qualitatively describe the microchemical changes the material underwent in the fretted region. Nanoindentation was used to compare microstructural properties inside and outside the fretting scar after fretting at different temperatures. COF measurements showed that APMT steel's COF and wear decreases with temperature up to 350 °C.