Probability based ranking approach for twin variant selection in an α-Zr alloy

Abstract

The ability to predict the formation of twin variants during deformation is essential for modelling the mechanical response of a material. The present study aims to provide a criteria for twin variant selection in an α-Zr alloy. Here Zircaloy-4 was uniaxially deformed at 25 and 300 °C to strain of 0.10 leading to formation of {101¯2}1¯011 tensile twins. Twin variants were characterized using electron backscatter diffraction for their dependency on commonly used geometric factors i.e. Schmid and geometric compatibility factor. It was shown that twin variants do not always form based on a single criterion. Slip traces and their relation to twins in the neighbouring grain were analysed. A probability based ranking approach for twin variant selection considering a combination of both Schmid and geometric compatibility factors is proposed. The approach was based on the probability of the occurrence of two events, (i) occurrence of either slip or twin and (ii) transmission between slip-twin events across the grain boundary. Two mechanisms as consequence of both (i) and (ii) were considered – mechanism Awhere twin formation is by the activation of either slip or twin system in the neighbouring grain, and mechanism B where active slip to twin or twin to twin transmission takes place across the grain boundary. The fraction of twins formed by mechanism A was seen to be higher than those by Schmid and geometric compatibility factor taken separately.