Electron beam irradiation induced metastable phase in a Mg-9.8 wt%Sn alloy

Aberration-corrected scanning transmission electron microscopy has been used to study a novel metastable phase, designated as beta '' phase, induced to form by electron beam irradiation in a Mg-9.8 wt.%Sn alloy. This phase is spherical in three dimensions, having a D0(19) structure with the lattice parameters of a = 0.642 nm, c =0.521 nm and space group of P6(3)/mmc. Its chemical formula is Mg3Sn, like the beta' metastable precipitate phase. The orientation relationship between the beta '' phase and the alpha-Mg matrix is such that [2 (1) over bar(1) over bar0](beta '')//[2 (1) over bar(1) over bar0](alpha) and (0001)(beta '')// (0001)(alpha). Its formation involves solely the ordering of Sn atoms in the solid solution magnesium matrix. First-principles calculations indicate that the formation of the beta '' phase is energetically favored. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.