Twin boundary activated alpha -> omega phase transformation in titanium under shock compression

HX Zong and XD Ding and T Lookman and J Sun, ACTA MATERIALIA, 115, 1-9 (2016).

DOI: 10.1016/j.actamat.2016.05.037

The role of grain boundary structures on the shock response of hexagonal-close-packed (hcp) metals is little understood. We use molecular dynamics simulations to investigate deformation mechanisms in shock compressed Ti bicrystals with three types of grain boundary (GB) microstructure. Our results show the shock response of phase Ti polycrystals are influenced by the GB characteristics, i.e., elastic shock wave induced inelastic deformation occurs on both sides of the 10 (1) over bar2 coherent twin boundaries (CTBs) but only on one-side of the symmetric incoherent twin boundaries (ITB) or 1 (2) over bar 10 tilt grain boundaries regions. In particular, we find that the elastic shock wave can readily trigger the alpha -> omega to transformation at 10 (1) over bar2 CTBs but not the other two GBs, and the alpha -> omega transformation at CTBs leads to considerable wave attenuation (i.e., the elastic precursor decay). Combined with first principle calculations, we find that CTBs can facilitate the overcoming of the energy barrier for the alpha -> omega transformation. Our findings have the potential to influence interface engineering and materials design under extreme conditions. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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