Ridge-twin boundaries as prolific dislocation sources in low stacking-fault energy metals and alloys

Dislocation activities are crucial in facilitating plastic deformation, even in metals that are prone to deformation twinning. We have discovered a novel type of prolific dislocation sources, which reside on nano-sized ridges along the borders between different twin variants in low stacking-fault energy (SFE) materials. These sources act as dislocation generators that promote dislocation interaction and accumulation, spreading plastic strain and leading to robust strain hardening at the early stages of plastic deformation. Molecular dynamic simulations indicate that the formation of nano-sized ridge-twin structures is energetically favorable at the junctions between multiple twins, explaining why such structures are ubiquitous in low-SFE materials. Decreasing the SFE can significantly increase the population of ridge-twin boundaries, facilitating strain hardening to sustain the stability of plastic flow. These findings provide new insights into the origin of dislocation plasticity and the high early-stage strain hardening rate in low-SFE materials.