hcp -> omega phase transition mechanisms in shocked zirconium: A machine learning based atomic simulation study

HX Zong and YF Luo and XD Ding and T Lookman and GJ Ackland, ACTA MATERIALIA, 162, 126-135 (2019).

DOI: 10.1016/j.actamat.2018.09.067

There has been much controversy over the behavior of zirconium under shock strong enough to cause the pressure-induced hcp -> omega phase transformation. Due to the short time- and length scales involved, direct measurements of the microstructure are extremely challenging. We have performed molecular dynamics simulations to investigate this issue, with Zr described by a machine-learned interatomic potential. Two different orientation relationships (ORs) between the hcp and omega phases are observed under shock driven conditions. Unlike the case with Ti that is in the same group, the ORs between the hcp and omega phases show less anisotropic phase transition sensitivity and in most cases follow the Silcock relationship with(0001)(alpha)parallel to(1 (2) over bar 10)(omega). Furthermore, we find that the alpha -> omega transformation in shocked Zr occurs via an intermediate metastable bcc structure during the loading process, whereas no such in-termediate is found during the reverse omega -> alpha transition when the shock releases. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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