Low cycle fatigue properties and fracture mechanisms of M38 nickel base superalloy at high temperature

Low cycle fatigue tests of the cast nickel base superalloy M38 have been conducted at 900 degrees C in air under fully reversed total strain control, strain ratio of -1 and the strain rate of 1 X 10(-2) s(-1). After failure, the fracture surfaces and longitudinal sections of the specimens were examined using SEM. Experimental results revealed that the fatigue property of M38 is similar to that of IN738LC. At high strain amplitudes, crack tended to initiate at the stress concentration sites such as surface carbides. While at low strain amplitudes, oxidation played an important role on crack initiation. The Cr-rich surface connected grain boundaries and Ti-rich surface carbides were observed to be favorable crack initiation sites. Under all strain amplitudes,,,the crack propagation modes were transgranular.