Unveiling deformation twin nucleation and growth mechanisms in BCC transition metals and alloys

JW Xiao and LY Zhu and R Wang and C Deng and ZX Wu and YT Zhu, MATERIALS TODAY, 65, 90-99 (2023).

DOI: 10.1016/j.mattod.2023.03.028

Twinning provides critical stress-relieving and flaw tolerance in body- centred cubic (BCC) transition metals (TMs) when dislocation plasticity is suppressed. Twin nucleation and growth mechanisms have been studied for over half a century without a consensus. Here, we use a reduced- constraint slip method to unveil the path to twin nucleation, growth and associated energy barriers in the entire BCC TM family. Twinning is surprisingly but essentially controlled by a normalized energy difference g between the hexagonal close-packed (HCP) and BCC structures in elemental TMs, and can be effectively tuned and quantitatively predicted by first-principles calculations in TM alloys. Fracture mechanics theory with g-based barriers enables predictions of critical solute concentrations to activate twinning and reverse ductile-to- brittle transitions in BCC TMs, as demonstrated in WRe alloys. The computational approach provides a unified and quantitative method to predict twinning and a practical tool for rapid screening of alloy compositions ensuring ductile behaviour.

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