Microstructure characterization and dynamic recrystallization behavior of Ni–Cu alloy during hot deformation

Abstract

Flow curve and microstructure of Ni–30Cu alloy were studied after hot compression at 1150 °C and strain rate of 0.01 s−1. The stress-strain and work hardening rate curves showed a weak peak at strain of 0.32, followed by a slight dynamic softening. The dominant microstructural mechanisms in low (0.1–0.23) and medium strains (0.23–0.32) were dynamic recovery and dynamic recrystallization, respectively. Microstructural characterizations by electron back scattered diffraction (EBSD) showed that continuous dynamic recrystallization brings about after the peak strain (ε = 0.32) and leads to grain refinement. It was found that the twin boundaries help to activate a grain dissociation mechanism which works as a new variant of continuous dynamic recrystallization. The grain boundary maps developed by EBSD showed that new twin boundaries form through the evolution of low angle grain boundaries. This step, named as “recovery twinning”, was identified as the origin for the observed twinning-assisted continuous dynamic recrystallization (TCDRX). The Kocks-Mecking dislocation evolution model was modified in order to take the dynamic softening by TCDRX into account and describe the variation in the frequency of high angle grain boundaries with strain. Model predictions were validated and confirmed by the experimental results.