Formation Formation of and interaction between β′F and β′ phases in a Mg-Gd alloy

This study reports the co-existence of beta' and beta'(F) phases and their interactions in an aged Mg-Gd alloy. Observations made from high-angle annular dark-field scanning transmission electron microscopy reveal that the beta' and beta'(F) precipitates form linear chains along {1 (1) over bar 00}alpha and within each chain they have an alternate distribution. Four types of interfaces exist between the adjoining beta' and beta'(F) precipitates, and one of them is the most frequently observed. The interaction between beta' and beta'(F) precipitates is examined using first-principles density functional theory computations and phase field simulations. Our calculation and simulation results reveal that the beta' and beta'(F) phases can form simultaneously because of similar values of their formation energy. The alternate distribution can effectively reduce the magnitude of the tensile stress around, and the compressive stress in and around the beta' precipitates. One of the four types of interfaces has a more negative formation energy, and as a result, it is most frequently observed. (C) 2017 Elsevier B.V. All rights reserved.