The effect of test temperature on the intergranular cracking of Nb-A286 alloy in low cycle fatigue

The continuous low cycle fatigue behaviors of a Fe-base superalloy, Nb-modified A286 alloy, have been evaluated at the test temperatures of 650°C and 350°C under various total strain ranges. It was found that the change of the slope in the Coffin–Manson plot was closely related to the fatigue cracking with the test temperature. In the high temperature low cycle fatigue (HTLCF) of Nb-A286 alloy, the fatigue cracking exhibited the intergranular mode at 650°C and the transgranular mode at 350°C. The intergranular fatigue cracking at 650°C was due to the precipitation of the η phase at the grain boundary assisted by the applied stress during low cycle fatigue. It is investigated whether the η precipitate at the grain boundary provides the site for the grain boundary cavitation, which induces the intergranular cracking in low cycle fatigue. This is confirmed by the results of low cycle fatigue at 25°C after heat treatment which forms the η phase at the grain boundary.