Abstract
The creep strength of single crystals of Ni-base superalloys has been interpreted in terms of the Schmid factors and multiplicity of {111} ‹112› type slip systems in the intermediate temperature ranges. {111} ‹112› type slip greatly decreases creep rupture life even in the third generation alloys which contain Rhenium by strain softening. Therefore, it is very important to investigate strain softening behavior of Ni-based superalloys to put advanced superalloys to practical application. The purpose of the present investigation is to study the strain softening in the creep deformation and to understand the resultant changes of creep behaviors on each orientation. It was found that strain softening was occurred by ‹112› viscous slip and deformation twinning in the [001] and [011] orientations, respectively, and that there was incubation period prior to strain softening. In the [111] creep, strain softening was not observed because it is very difficult for dislocations to cut the precipitates.
