High-temperature tensile and creep behaviour of Inconel 625 superalloy sheet and its associated deformation-failure micromechanisms

Thermal tensile and creep properties provide important information for selecting the suitable service conditions for metal materials. In this study, the effects of temperature on the tensile and creep properties, microstructure evolution, and deformation mechanisms of thermal-rolled Inconel 625 sheets were systematically investigated at 650 and 750 °C. The results showed that type B + C serrations dominated the tensile deformation at 650 °C. As the tensile temperature increased to 750 °C, type C serrations occurred in the early stages of the deformation and gradually transformed to type B serrations with the increase of the strain level. The microscopic observations through transmission electron microscopy (TEM) indicated that type B and C serrations were related to the carbon atom–moving dislocation interactions and nucleation–growth process of twin deformation, respectively. Moreover, the creep tests at 650 °C exhibited a better creep resistance than that at 750 °C. The results from the electron backscatter diffraction and TEM indicated combined grain boundary sliding and dislocation slipping as the main creep mechanisms at 650 °C. Moreover, the creep stress can accelerate the precipitation of the γ″ phases at 650 °C, which plays an important role in improving creep resistance, thereby improving the efficiency in strengthening Ni-based alloys. In addition, δ phase precipitation occurred during creep loading at 750 °C. The δ phases/matrix interfaces can act as nucleation sites to initiate dynamic recrystallization, which greatly affects the reduction of the work hardening rate and consequently, decreasing the creep resistance at 750 °C.