Stability and strain-driven evolution of β′ precipitate in Mg-Y alloys

Alloying Mg with rare-earth elements, such as Nd, Gd, or Y, enables hardening from the precipitation of metastable coherent phases during aging at low temperatures. While the aging potential of binary Mg-Nd alloys is relatively limited due to the nucleation of coarse beta(1) and beta precipitates at the expense of the strengthening beta''' precipitates, binary Mg-Y alloys exhibit exceptional stability of the strengthening coherent Os' phase when aged at 200 degrees C. Through combination of high-resolution characterization, density functional theory calculations, and finite-element elasticity studies, we demonstrate that the strengthening beta s(') phase is thermodynamically stable at low temperatures (as opposed to metastable as in other Mg-RE binaries) and that misfit strains play a key role in not only controlling precipitate structure and morphology but also their unusual evolution into an interconnected network. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.