Failure-mode dependence on the formation of deformation twinning in the fourth-generation single crystal Ni-based superalloy at high temperatures

In this work, the twinning-related deformation mechanisms under different failure modes of a fourth-generation single crystal (SX) superalloy at high temperatures were investigated. Notably, the twinnability of alloy increased in the sequence as follows: pure tension, in-phase (IP) thermal mechanical fatigue (TMF), isothermal low cycle fatigue (LCF), hot compression, out-of-phase (OP) TMF. High-temperature compressive loading which facilitated the successive operation of {111}(1 1 2) viscous slipping, was indispensable for the nucleation of micro-twins. However, this stimulative effect could be markedly offset by the co-existence of high-temperature tensile loading. Moreover, the activation of different {11 1}(1 1 2) slipping systems as well as potential interactions between stacking faults played a significant role in the formation and thickening processes of deformation twins. In the experimental alloy system, the presence of deformation twins was attested to impair the fatigue resistance of the specimen. These findings provided new insights for ensuring the safe service of the fourth-generation SX superalloys.