STOCHASTIC PROCESSES OF {1012} DEFORMATION TWINNING IN HEXAGONAL CLOSE-PACKED POLYCRYSTALLINE ZIRCONIUM AND MAGNESIUM

摘要

Deformation twinning is an important mechanism for metals with hexagonal close-packed (hep) crystal structures such as titanium, magnesium, beryllium, and zirconium, as well as metals with other low-symmetry crystal structures. This article presents a multiscale constitutive model for the plastic deformation of hep polycrystalline metals that is built upon the viscoplastic self-consistent (VPSC) polycrystal scheme. This framework includes a novel probabilistic model for predicting when, where, and which variants nucleate, a dislocation density model for crystallographic slip, and a micromechanical model for twin lamella thickening and twin reorientation. Length scales of an individual slip or twinning system and the polycrystalline aggregate are interactively connected. Here, this constitutive model is applied to high-purity magnesium (Mg) and zirconium (Zr) deformed under loading conditions where twinning is intense. Correlations are made between the formation of deformation twins, bulk stress-strain behavior and texture development, and individual grain properties such as size and crystallographic orientation.