Unusual substructure evolution and post-dynamic recrystallization effects on flow softening mechanism in a γ^′-free Co-base superalloy

Motivation for this study was the absence of any report of stacking fault energy (SFE) estimate and post-dynamic recrystallization (PDRX) effects at temperatures >1000 °C in γ′-free Co-base superalloys. Therefore, the substructural evolution during hot compression of Co-22Cr-22Ni-14W-2Fe-0.1C superalloy (H188) at temperatures (1050–1150 °C) and at 10−1 s−1 was studied. Unusual substructural features viz. extrinsic stacking faults, dense dislocation walls, microbands, and subgrains were observed with an increase in strain (0.01–0.70), even at 1100 °C. Denoised electron backscattered diffraction data revealed an enormous increase in overall recrystallized (PDRX+DRX) fraction from 30 to 75% with increase in temperature from 1050 to 1100 °C at ε=0.7. Comprehensive microstructural analyses suggest that continuous dynamic recrystallization is the dominant flow softening mechanism in low SFE (estimated to be 14 ± 2.0 mJ/m2) alloy H188. However, the PDRX effects triggered by the presence of higher stored energy and recrystallized nuclei contributing to a massive increase in recrystallized fraction at 1100 °C.