High-temperature low-cycle fatigue behavior of HAYNES® 230® superalloy

Total strain-controlled low-cycle fatigue tests and stress intensity factor range (DeltaK)-controlled crack growth tests without and with hold times, as well as stress relaxation tests were conducted at high temperatures for a nickel-chromium-tungstenmolybdenum HAYNES 230 superalloy sheet material. The influences of test temperature and hold time on low-cycle fatigue and crack growth behavior were determined. The low-cycle fatigue life shows a strong dependence on test temperature and hold time. At all test conditions used in this investigation, the alloy exhibits strain hardening followed by softening. The crack growth rate per cycle was found to increase with longer hold time. Scanning electron microscope (SEM) observations show that crack initiation occurred in either transgranular or intergranular mode, while the crack propagated in either transgranular or mixed transgranular and intergranular mode. These cracking modes were dependent on test temperature and hold time.