Twining and dynamic recrystallization in austenitic Alloy 718 during friction welding

Quantitative boundary misorientation analysis verified that discontinuous dynamic recrystallization (DDRX) was the primary grain refinement mechanism in friction welding of Alloy 718. Two models were developed to explain the formation mechanism of intragranular twins and intergranular twins, respectively. Intragranular twins were caused by grain boundary growth incidents. After twin initiation, the twin boundary migrated toward the plastic-deformed grain interior to reduce the stored energy. Additionally, intergranular twin boundaries were ascribed to boundary growth stagnation. When boundary growth stagnation occurred, twin boundaries could form and altered the orientation of the boundary migration front, so that boundary migration could progress, leaving a single twin boundary behind.