Temperature dependence of deformation behavior, microstructure evolution and fracture mechanism of Inconel 625 superalloy

Highlights: • Tensile behavior and fracture mechanism were closely dependent on temperature. • Serrated flow was related to Laves phases-dislocations interaction and deformation twins. • Dynamic recrystallization characteristic during tensile deformation was revealed. -- Abstract: The temperature effect on deformation behavior, microstructural evolution and fracture mechanism of Inconel 625 superalloy sheet were systematically investigated in a wide temperature range from room temperature (RT) to 950 °C. Tensile temperature was varied in increments of 50 °C after reaching 500 °C. Obvious serrations occurred at the medium temperature range and evolved in the sequence of B→B+C→C with increasing temperature. Microscopic observations from transmission electron microscopy (TEM) indicated that the interaction between C14-Ni₂Nb Laves phases and mobile dislocations was found to be responsible for the type B serration, and the type C serration was associated with nucleation and growth of deformation twins. Recrystallized grains were observed above 850 °C, and results from electron backscattered diffraction and TEM showed that both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) take place, while CDRX was the secondary nucleation mechanism. The stress concentration caused by Nb-rich phases was responsible for crack nucleation at tensile temperatures below 650 °C. The combined action of slip bands impingement on grain boundaries and stress concentration caused by Nb-rich phases led to crack initiation at the tensile temperature of 750 °C and 850 °C. Void nucleation at triple junctions of grain boundaries resulted from grain boundary sliding should be responsible for the ductile fracture at 950 °C.