Stress corrosion testing of CMSX-4, CM247LC DS and IN6203DS Ni-base superalloys

The combination of stress and hot corrosion may result in Ni-base superalloys experiencing stress corrosion cracking, of which, the mechanisms are little understood. The aim of this research was to enhance the understanding by performing a series of stress corrosion exposures, at temperatures of 550, 500 and 450 °C, on: CMSX-4, CM247LC DS and IN6203DS superalloys. After completing the exposures, the superalloys were ranked with respect to the severity of the cracking experienced (CMSX-4 showing the worst severity, followed by CM247LC DS and then IN6203DS which showed no evidence of cracking at all) and the ranking appeared to be correlated to the gamma prime volume fraction. This suggests the gamma prime volume fraction is associated with the crack mechanism with lower values increasing the resistance to stress corrosion cracking. From the findings of this research, a new crack initiation/propagation mechanism is proposed which is based on a summation of stresses that includes those associated with the gamma prime