Low cycle fatigue behavior of a cast nickel base superalloy M963 at elevated temperature

Low cycle fatigue tests for cast nickel base superalloy M963 have been conducted at 900 degrees C in air under fully reversed total strain control cycling at strain rates of 4x10(-3) s(-1) and 1x10(-4) s(-1). The experimental results showed that at the same strain amplitude, fatigue life at low strain rate was shorter than that at high strain rate, which is attributed to time dependent damage mechanism such as oxidation. SEM observation revealed that the cracks initiated at the surface-connected carbides and/or casting micropores at subsurface. When the strain rate was lower, some of the cracks tended to initiate at interdendritic regions and then propagate along interdendritic regions. In all tests, the cracking mode was transgranular.