Abstract
The effect of tensile strength and ductility on high temperature low cycle fatigue of cast Ni-base superalloys was studied. The main results obtained are as follows :
(1) At total strain ranges above 0.01, where plastic fatigue was dominant, fatigue lives of high ductility alloys (MM247 as cast and HT, IN738LC as cast, TM-321 HT, HT standing for heat-treated) were longer than those of low ductility alloys (TM-185 as cast, TM-49 as cast). At total strain ranges below 0.005, where elastic fatigue was dominant, fatigue lives of high strength alloys (TM-185 as cast, TM-321 as cast and HT, MM247 as cast and HT) were longer than those of low strength alloy (IN738LC as cast).
(2) High temperature low cycle fatigue lives of cast Ni-base superalloys could be roughly estimated by the Universal Slope method combined with 10% rule.
(3) Fatigue crack was considered to initiate at the surface-connected grain boundary, and crack propagation was mixture of intergranular and transgranular types.
(4) In the long life range, preferential oxidation of surface-connected grain boundaries was considered to reduce fatigue life.
