Precipitation evolution induced by electron beam irradiation in Mg-RE alloys

At present, it is of important significance for the microstructure design of rare earth magnesium (Mg-RE) alloys to comprehend the evolutionary mechanisms of metastable precipitation phases. In this study, a phase transition from βS′ to β1 caused by electron beam irradiation is studied particularly in a Mg-Y-Ce alloy by means of atomic scale scanning transmission electron microscopy. Results show that the structural evolution from βS′ to β1 precipitates can be accomplished thoroughly within two minutes for a nanosized particle. It is mainly ascribed to the fact that the increasing heat and vacancy concentration generated by electron beam irradiation can greatly accelerate the atomic diffusion, especially along c-axis direction. It is confirmed that the phase transition from βS′ to β1 is segmented into the two stages, including the preceding diffusive and the subsequent displacive phase transitions. The findings will provide some useful clues to control effectively the morphologies of precipitates and the precipitation behaviors of Mg-RE alloys.