The Synergistic Effects of Energy Barriers and Shear Directions on Twinning in Face Centered Cubic Metals

Abstract

The formation of twins in face-centered cubic (FCC) crystals is influenced by both the energy barriers and associated shear directions; however, the synergy between both of these factors, if any, has heretofore never been studied before. In this study, we formulate and implement a theoretical framework to study 15 pure FCC metals in an effort to propose a twinning propensity descriptor to predict the tendency for twin formation in FCC metals. Our calculations demonstrate that deformation twins form readily in: Al, Ir, Ni, Rh, Co, Au, Cu, Yb, Ag, Sr, and Ca, but have difficulty forming in: Ce, Pt, Pb, and Pd, and this trend is consistent with available experiment results. Using this descriptor, we further predict that in the case of Cu-Al alloys the highest twinning propensity is achieved at ~6 at. % Al concentration, which is also consistent with experimental observations. These results provide insight into the nature of deformation twins, and furthermore help establish the framework necessary to design FCC metals and alloys with a high tendency for twin formation.

Keywords: Face-centered cubic crystals, Intrinsic energy, Shear direction, Twin, Density-functional theory