Grain Boundary Engineering of Strain-Annealed Hastelloy-X

The present study investigates the occurrence and effectiveness of the dissociation mechanism of Σ3 CSL boundaries into its variants such as Σ9 and Σ27a-b during strain-annealed grain boundary engineering (GBE) of Hastelloy-X. Multiple cold-rolling strain levels and annealing conditions are studied and it is observed that the density of ∑3 boundaries decreases proportionally to the amount of strain induced boundary migration (SIBM) during the GBE process. The dissociation mechanism of Σ3 annealing twins is activated at the onset of SIBM, causing an increase in the density of the Σ3 n variants. It is shown that at high annealing times or temperatures, the rate of generation of CSL boundaries through dissociation mechanism is lower than their annihilation rate. It is further suggested that the dissociation mechanism of ∑3 boundaries during GB migration is more efficient when the amount of applied strain prior to annealing is kept low, thus promoting disruption of the random GB network.