Micro-scale local damage mechanisms and life prediction method of the fourth-generation single crystal superalloy under thermal-mechanical fatigue

During the in-service of single crystal (SX) turbine blades, the ever-changing temperature and stress at starting-up/shutting-down stages would inevitably cause fatal damages to SX superalloys by means of low-cycle fatigue (LCF) and thermal-mechanical fatigue (TMF). In this work, the micro-scale local damage originated from micro-pores and crack tips during high-temperature cyclic deformation was disclosed. The introduction of local micro-defects significantly affected fatigue life and favorably facilitated local γ′-degradation, by means of excessive superdislocations (LCF and in-phase TMF) and twinning/stacking faults (LCF and out-of-phase TMF) shearing. Furthermore, relationships between both the macroscopic/micro-scale damage mechanisms and different strain energy components have been subsequently established. Accordingly, the high-accuracy fatigue life prediction has been achieved in fourth -generation SX superalloy system, based on the method of supplement and optimization of the hysteresis energy into total strain energy. These achievements contribute to the development of novel superalloy materials and safe operation of advanced aero-engines.