The effect of long term high temperature annealing on twinning and detwinning of the wrought Ni3Al-based alloy

The effect of annealing at 1180 °C from 10 to 40 h on a wrought Ni3Al-based alloy was investigated using EBSD, SEM and TEM. We characterized the grain boundary character distribution (GBCD) of the annealed alloy and found that the frequency of Σ3 twin boundaries (TBs) decreased with the long term exposure. Both twinning and detwinning proceeded in the post-recrystallized microstructure during the thermal hold. The 10-hour annealing resulted in the highest frequencies of Σ3 TBs and the high order TBs. Σ3 TBs evolved into twin junctions via meeting of bulging corner twins and colliding of the nonparallel twins. With prolonged annealing, detwinning prevailed, shown by the decreasing frequency of Σ3 TBs, with simultaneous increase of fraction of substructured grains and subgrain boundaries (SGBs). Detwinning occurred via disintegration of primary twins, and dissociation of secondary microtwins/nanotwins that leads to partial formation of SGBs.