Yield strength anomaly evaluation of W-free Co-Ni-Al-based superalloys during high temperature tensile tests

High temperature tensile behaviors of two W-free Co-Ni-Al-based γ'-strengthened superalloys at 773 K ~ 1073 K were investigated. The tensile strength and elongation of two superalloys decrease with increasing temperature. The fracture mechanism changes from dimple fracture to brittle fracture. A detailed observation of the fracture shows that the intermediate temperature embrittlement caused by decohesion of slip plane plays a significant role in reducing high temperature performance. Both superalloys reach to peak yield strength at 923 K. Occurance of yield strength anomaly (YSA) is derived from the synergistic effects of dislocation locking strengthening and dynamic strain aging strengthening. Dislocation cross-slipping hinders the dislocation migration. Dislocations' unpinning to the moving solutes increases the yield strength at 723 K ~ 973 K. A rapid weakening of grain boundaries strength decreases the yield strength at 1073 K.