Effect of test temperature on deformation microstructure and tensile property of a novel Ni-Co-based superalloy

The tensile behavior, deformation microstructures and failure mechanisms of a novel Ni-Co base precipitation-hardened superalloy, have been investigated at room temperature (RT), 450, 550, 650 and 750 °C. Deformation of the alloy at RT, 450, 550 °C is primarily mediated by dislocation slip and stacking faults while nano-sized deformation twinning is also involved at 650 and 750 °C. The yield and tensile strength decrease with increasing test temperature. In the temperature range of 450–650 °C, however, no obvious reduction in the yield strength and work-hardening rate at low strains is observed, which could be correlated to a high density of stacking faults or deformation twins. Low yield strength and work-hardening at 750 °C, could be related to the softening by thermal activation and the softening of γ′ particles caused by the repeated cutting via stacking faults or twins. However, as the testing temperature is over 450 °C, elongation of the alloy decreases significantly with increasing test temperature, which could be associated with intergranular cracking induced by stress-assisted grain boundary oxidation.