Abstract
The effects of grain boundary orientation and cyclic load on the creep and fracture behaviour of directionally solidified superalloy DZ17G have been investigated. The results show that grain boundary orientation has no effect on the creep deformation mechanism, but has a marked effect on the fracture mechanism. The creep fracture mechanism changes from a transgranular mode in longitudinal specimens to intergranular failure in transverse and inclined (45° to applied stress axis) specimens. Compared with constant load, cyclic load remarkably reduces creep life with the increment of cyclic frequency, but has no effect on the creep ductility. After careful examination of the transient response following the load changes, it is suggested that an intrinsic softening occurred during unloading, which accelerates the creep deformation rate on subsequent reloading, and the accumulation of this softening effect finally results in cyclic creep acceleration. The contribution of anelasticity has also been discussed.
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