The role of mechanical loading in bcc-hcp phase transition: tension-compression asymmetry and twin formation

In response to temperature or pressure changes, many body-centered cubic (bcc) materials undergo martensitic bcc-hcp phase transformation, which is known to produce rich martensite microstructure with internal twins. Mechanical loading is also known to have a huge impact on martensitic phase transformation. In this work, we integrate atomistic simulations with theoretical calculations to investigate the effect of mechanical loading on the martensite microstructure. The calculations of deformation gradients and transformation strains reveal that the { 10 1 ¯ 1 } transformation twins and { 10 1 ¯ 2 } transformation twins are favored by opposite loading directions. Furthermore, the initial { 112 } twin in the bcc phase is transformed into { 11 2 ¯ 2 } and { 11 2 ¯ 1 } twins after the phase transformation. The results reveal the critical role of mechanical loading in the formation of the specific transformation twinning, which could offer a novel strategy to engineer twin microstructure using designed thermomechanical processing.