Polymorphic nature of {332} 〈 113 〉 twinning mode in BCC alloys.

Unprecedented mechanical properties of the novel TWIP/TRIP titanium alloys are controlled by { 332 } < 113 > twinning and stress-induced martensitic transformation, which can operate separately, simultaneously or even in synergy, following a still unclear atomic-scale mechanism. Using ab initio calculations and experimental observations, we show that { 332 } < 113 > twinning can be described as a polymorphic solid-state transformation able to produce either twinned or martensitic structures with a unified transformation path. The required lattice strains and atomic shuffles are provided by the shear-shuffle mechanism of twin operation, of which trajectory, due to accompanied atomic relaxation, is not linear and strongly influenced by β phase stability. Plasticity of metastable alloys is extended by the concept of polymorphic deformation modes of which path is sensitive to the composition of the alloy, enabling stabilization of the intermediate transition states. [ABSTRACT FROM AUTHOR]