Topic: Deformation Twinning in Hexagonal Metals

Twinning and de-twinning, which are the dominant deformation mechanisms in hexagonal-close-packed (HCP) metals, exhibit more complex nucleation, propagation, thickening mechanisms than those in cubic structures (FCC and BCC). Specifically, twinning and de-twinning cause unidirectional shear and crystallographic reorientation, associated with atomistic shuffling. Due to the coupled movements of shear displacement and shuffle displacements, twinning mechanisms are subject to some debate among pure-shuffle vs shear-shuffle. Due to small shear vector associated with twinning disconnection, steps and facets are generally formed associated with the pileup of TDs. Understanding formation and motion of TDs/Steps/Facets is essential for describing the propagation and thickening of deformation twins. Due to multiple variants and twinning modes in HCP metals, there is a fundamental issue of determining the activated twinning modes and twin variants under a certain deformation condition. In this talk, I will focus on the fundamental understanding of nucleation, propagation, and interactions of deformation twins and the development of materials modeling tools for twinning at meso- and macro- scales as well as alloy design. These findings provide theoretical base for researchers to revisit experimental data, rebuild the frame of twinning mechanisms and advance the development of alloy design.