Solute/twin boundary interaction as a new atomic-scale mechanism for dynamic strain aging

Twinning is an important mechanism during the plastic deformation of materials with hexagonal-close-packed crystal structure. Strength and formability are critical properties for this family of structural materials and can consequently be improved by controlling twin nucleation and growth. Here, we study the effect of alloying elements on strain rate and temperature dependence of twin growth. Without using any fitting parameters, we derive an analytical model which takes atomic scale calculated parameters as input and predicts the equilibrium concentration of segregated solutes and strengthening due to solute-twin interactions. This model predicts the strain-rate/temperature conditions of negative strain rate sensitivity in titanium, under loading conditions that favor twinning, with oxygen interstitial. The predictions are in agreement with available experiments. Our findings present a new mechanism for dynamic strain aging as a result of solute segregation to the twin boundaries. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.