Microstructural effects on the fretting wear of Inconel 690 steam generator tube

Inconel 690 is used for steam generator tube in nuclear power plants. In this study, microstructural effects on fretting wear of Inconel 690 were investigated. To change the microstructure of test specimens, heat treatments were performed in two steps; solution annealing (at a high temperature) and thermal treatment (at a low temperature). Observations of microstructure indicated that the temperature and duration of solution annealing affect the grain size of Inconel 690. The carbide morphology along grain boundaries was affected mainly by duration and temperature of thermal treatment. The results of the wear test show that specimens with larger grain and coarse carbides along the grain boundaries have greater resistance to wear. Cracks were found in specimens with carbides along the grain boundary whereas few cracks were found in carbide-free specimens. The carbide along the grain boundary seemed to help form and propagate cracks in the specimens with carbides. On the other hand, the microhardness of specimens had no major role in fretting wear.