Date | Time
21/07/2014 | All Day
« Nucleation, Propagation and Interactions of Deformation Twins in Hexagonal-close-packed Metals
Dr Jian Wang de Materials Science and Technology Division, Los Alamos National Laboratory (E.U.)
Abstract Deformation twinning is a major mode of plastic deformation in hexagonal-close-packed crystals and exhibits more complex nucleation and propagation mechanisms than those in cubic structure. In this lecture, I highlighted several twinning-associated boundaries that play crucial roles in nucleation, growth, and interactions of deformation twins in hcp metals. According to microscopic characterizations and atomistic simulations, four types of boundaries are reviewed including (1) symmetrical tile grain boundaries (SCTGs) that favor twin nucleation or migrate based on twin dislocations, (2) prismatic-basal boundaries (PBs or BPs) associated with twin nucleation via pure-shuffle mechanism, (3) serrated coherent twin boundaries (SCTBs) associated with migration of twin boundaries via glide and climb of twinning dislocations, and (4) prismatic-prismatic (PPs) and basal-basal (BBs) boundaries associated with co-zone twin-twin interactions. More importantly, these boundaries affect twinning and detwinning processes that may correspond to twinning-induced hardening and seem universal associated with twins in hexagonal-close-packed metals. These findings provide theoretical base for researchers to revisit experimental data, rebuild the frame of twinning mechanisms including nucleation and propagation of twins, and advance the development of materials modeling tools at meso- and macro- scales as well as alloy design.