CYCLIC LIFE OF SUPERALLOY IN738LC UNDER IN-PHASE AND OUT-OF-PHASE THERMOMECHANICAL FATIGUE LOADING

The cyclic life of IN738LC, a widely used nickel base superalloy for b lades in stationary gas turbines, was investigated under thermo-mechan ical fatigue loading using a temperature variation range of 1023 to 12 23 K, with temperature variation rate in the range of 6 to 15 K/min. S imple thermo-mechanical cycles with linear sequences corresponding to in-phase (IP) and out-of-phase (OP) tests were performed. Both the IP and OP tests were carried out at different constant mechanical strain ranges varied between 0.8 to 2.0 % and at a constant mechanical strain rate of 10(-5) s(-1). Thermo-mechanical fatigue lives under both test conditions were compared with each other and with those of isothermal LCF tests at a temperature of 1223 K. The results show that the life under thermo-mechanical fatigue is strongly dependent on the nature of the test, i.e. stress controlled or strain controlled.