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Probability Based Ranking Approach to Twin Variant Selection: A Study on α-Zr Alloy

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Document pages: 35 pages

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 {1 0 1̅ 2}〈1̅ 0 1 1〉 twins. Twin variants were characterized using electron backscatter diffraction for their dependency on commonly used geometric factors i.e. Schmid and 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 on a 0.04 strained sample. A probability based ranking approach for twin variant selection considering a combination of both Schmid and geometric factors was proposed. The approach was based on the probability of the occurrence of two events, a) occurrence of either slip or twin and b) transmission between slip-twin events across the grain boundary. Two mechanisms as consequence of both (a) and (b) were considered – (1) twin formation by the activation of soft slip system in the neighbouring grain, (2) active slip to twin transmission across the grain boundary. Overall, the fraction of twins formed by the first mechanism was the highest among all the geometric factors. Lastly, a method for the selection of neighbouring grain (among multiple neighbours of the grain) from which a twin should form was suggested.

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