Twinning dislocation and twin propagation process in a nickel-base single crystal TMS-82 superalloy

Abstract

AbstractThermomechanical fatigue cyclic loading tests have been carried out along the <001> orientation and the formation of twins during thermomechanical fatigue processing has been studied in detail in a nickel-base single crystal TMS-82 superalloy. The twinning dislocation is determined to be 1/6<112> in the γ′ phase except for the 1/3<112> dislocation, which operates on every successive {111} plane. The 1/6<112> twinning dislocations can move independently in both γ and γ′ phases. Although movement of a single 1/6<112> twining dislocation may destroy the ordering of γ′ phase, its existence is rationalized on the basis of crystallographic analysis. The movement of a 1/3<112> dislocation on a single {111} plane will lead to a high-energy stacking sequence of head-to-head of two neighboring {111} layer atoms in the L12structure. Pre-existing dislocations have a significant effect on the growth of deformation twins. In the dislocation-free area, the twin can propagate without any notable impediment to lead to a twin plate with equal width. High dislocation density may hinder the propagation of twins to varying degrees.