The effect of environment and structure on creep fatigue crack propagation in a P/M astroloy

The effect of environment and structure on creep fatigue crack propagation in a P/M Astroloy has been investigated by performing tests in air and in vacuum at 650 C and 750 C. Complex mechanical and environmental interactions have been revealed at 750 C temperature at which the da/dN-ΔK relationship obtained in air appears to be highly dependent of the initial ΔK values applied at the beginning of the creep-fatigue test. The effect of grain size with smooth grain boundaries appears to be strongly related to environmental effects rather than to creep properties. A serrated grain boundary morphology considerably improves crack growth resistance at 750 C under creep-fatigue conditions. (orig.)