Rotational And Translational Domains Of Beta Precipitate In Aged Binary Mg-Ce Alloys

The structural evolution from beta(1) (Mg3Ce) to beta (Mg12Ce) precipitates, which takes place at the over-aged stage of binary Mg-Ce alloys, are investigated by high-angle annular dark-field scanning transmission electron microscopy. The structural transformation mainly occurs in the {111} beta 1 crystallographic planes, where the newly formed beta lattices exhibit two categories of domain structures, namely rotational and translational domains. The rotational domain is composed of three beta domains (beta(RA), beta(RB) and beta(RC)), which are related by a 120 degrees rotation with respect to each other around the < 111 >(beta 1) axis of their beta(1) parent phase. The {111}(beta 1) crystallographic planes can provide four sets of sublattices with the same orientation for an initial nucleation of beta lattice. It leads to the formation of four translational beta domains (beta(TA), beta(TB), beta(TC) and beta TD), among which any two differ by a vector of 1 /6 < 112 >(beta 1). We deduce theoretically that there exist twenty-four beta domains during this transition. However, considering the interfacial misfit, only one-third of domains can grow up and eventually forms beta ribbon. Furthermore, a majority of beta ribbons overlap partially beta(1) plate, which is beneficial to relax interfacial strain among beta, beta(1) and alpha-Mg matrix (alpha/beta/beta(1)). The configuration of multiple beta domains can effectively regulate interfacial misfit of alpha/beta and beta/beta(1), which are responsible for enhancing the hardness and strength of Mg-Ce alloy. Additionally, this study aims to provide some clues to improve the over-aged performance of magnesium alloys by constructing beta domains and optimizing the alpha/beta/beta 1 interface. (C) 2020 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.