Full-stage low cycle fatigue failure mechanisms of [001], [011] and [111] oriented single crystal superalloys by a combination of SEM, TEM and acoustic emission

In this paper, full-stage low cycle fatigue failure mechanisms of nickel-based single crystal superalloy with [001], [011] and [111] orientation at 530 °C were systematically studied by employing acoustic emission (AE), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). [001], [011] and [111] specimens show cyclic stability, slight cyclic hardening, and obvious cyclic hardening, respectively. Cyclic stability response of the [001] orientation is related to short dislocation multiplication in early stage and dislocations cutting the γ′ during crack propagation, finally failure occurs in the form of extended steps. Moreover, long curving and immovable dislocations accumulate and tangle in the γ-channel during crack initiation in the [011] specimen and cross-slip motion of dislocations during crack propagation, resulting in slight cyclic hardening, and ultimately cleavage-like fracture occurs. With respect to the cyclic hardening in the [111] specimen, short dislocations pile up at the γ/γ′ interface in the early stage, the subsequent formation of dislocation networks and parallel dislocations further reduce the probability of dislocation interactions among different slip systems, ultimately fracturing along the {111} crystallographic plane. Revealing the differences in full-stage failure mechanisms among the three orientations lays a solid theoretical foundation for applications.