Driving force of zero-macroscopic-strain deformation twinning in face-centred-cubic metals

Zero-macroscopic-strain deformation twinning (ZMS-DT) is widely observed in many face-centred-cubic (FCC) metals and alloys. However, the driving force of ZMS-DT is a controversial issue and has not been fully clarified for a long time. Based on molecular dynamics simulations to various FCC metals, we found that ZMS-DT, i.e. Σ₃{112} incoherent twin boundary migration can be driven by simultaneously applying both normal and shear strains/stresses to the twin boundary (TB), and changing the sign of the normal or the shear strain/stress can change the direction of the incoherent TB migration. With analysing the results of atomistic strain energy calculation and anisotropic elasticity theory, we revealed the strain energy imbalance, which originates from elastic anisotropic response of materials, between the two sides of the twin boundary under normal–shear strain (or stress) coupling condition essentially drives the TB migration and twin growth. Eventually, we deduce that the elastic anisotropy ratio can be one of the key material constants which affect the twinnability of FCC metals.