Twin-type dependent deformation mechanism in nano-twinned titanium: a molecular dynamics simulation study

The twin-type dependent deformation mechanisms in nano-twinned titanium (Ti) were systematically investigated through molecular dynamics (MD) simulations based on bicrystal and equiaxed nano-twinned models. Three fundamental insights include: 1) {11-22} TBs exhibit weaker migration capability compared to {10-12} TBs, enhancing the dislocation blocking efficacy and thus increasing the strength of {11-22} nano-twinned Ti. 2) {11-22} nano-twinned Ti presents a Hall-Petch strengthening regime when above the critical length (grain size = 15 nm, TB spacing = 3 nm). Below the critical length, increased TB migration coupled with grain boundary-mediated plasticity induces continuous softening, demonstrating a distinct inverse Hall-Petch relationship. 3) The high mobility of {10-12} TBs facilitates both TB migration and detwinning phenomena. Strength evolution displays non-monotonic dependence on TB spacing: Progressive softening occurs from 6 nm to 3 nm spacing due to enhanced TB migration activity, while sub-3 nm spacings trigger detwinning-induced TB density reduction, paradoxically restoring strengthening through diminished migration pathways. 4) The competition between the softening effect induced by TB migration and detwinning and the strengthening effect caused by dislocation-TB interaction determines the strength of nano-twinned Ti. By reasonable design and regulation of TB mobility and spacings, it is expected to maximise the TB-induced strengthening effect in nano-twinned materials. Highlights: Deciphered twin-type dependent deformation mechanism in nano-twinned Ti via MD simulations of bicrystal and equiaxed-grained nano-twinned models. {11-22} TBs exhibit weaker migration capability compared to {10-12} TBs, enhancing the dislocation blocking efficacy and thus increasing the strength of {11-22} nano-twinned Ti. Identified critical grain size (>15 nm) and TB spacing threshold (>3 nm) for effective dislocation-TB interaction-induced strengthening in {11-22} nano-twinned Ti. Elucidated dual softening mechanisms (TB migration and detwinning) in the non-monotonic evolution of strength with TB spacing in {10-12} nano-twinned Ti. Clarified competition mechanism between dislocation-TB interaction-induced strengthening and boundary migration-induced softening in nano-twinned Ti.