Enhanced strength and ductility at 760 °C of a Ni-based superalloy induced by pre-strain treatments

The effects of pre-strain on the microstructural evolution and mechanical properties of a Ni-based superalloy were systematically investigated. Microstructural characterization was performed using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) to analyze the as-received and pre-strained conditions, as well as after tensile testing. The results demonstrate that the yield strength at 760 °C increases with pre-strain up to 30%, reaching a peak value of 1220 MPa (a 37.2% improvement over the initial state). This enhancement is attributed to the increased density of slip bands, deformation twins, stacking faults, and their coupled structures. Notably, when the pre-strain exceeds 30%, the ductility recovers to a level comparable to the initial state while maintaining a yield strength increase of over 10%, achieving an optimal balance between strength and ductility. The sustained high strength is primarily due to the increased density and strengthening effect of deformation twins. Concurrently, the improved ductility arises from the softening effects of accelerated dynamic recovery and recrystallization, as well as the precipitation of M 23 C 6 carbides at sub-grains and twin boundaries.