Effects of temperature on superplastic and fracture behaviors of a Ni-Co-based superalloy

The effects of deformation temperatures on the superplastic behavior, microstructure evolution, and failure mechanisms of Ni-Co-based superalloy were analyzed at temperatures ranging from 900 to 1140 °C. The superplastic-tensile temperatures have significant effects on flow behavior, which shows distinctive features of dynamic recrystallization (DRX). The alloy exhibits a striking increase in elongation with increasing the superplastic-tensile temperature to 1100 °C, reaching 1760 %. The deformed microstructure was characterized using SEM, EBSD, and TEM. As the superplastic-tensile temperatures increased, the DRX-grain fraction increased. The superplastic deformation of the alloy is primarily governed by discontinuous-DRX (DDRX) mechanism. Continuous-DRX (CDRX) had a significant effect at 900 °C and occurs as an assistant mechanism during superplastic deformation of the alloy at elevated temperatures. The fracture at 900 °C was initiated by a combination of intergranular and micro-void coalescences, while the pure intergranular fracture takes place above 1050 °C. Meanwhile, the micro-void coalescence has only a minor effect on the fracture behavior at 1140 °C.