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

Unprecedented mechanical properties of the novel TWIP/TRIP titanium alloys are controlled by 332 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 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.