Interfacial dislocations dominated lateral growth of long-period stacking ordered phase in Mg alloys

Abstract

Understanding the interface between strengthening precipitates and matrix in alloys, especially at the atomic level, is a critical issue for tailoring the precipitate strengthening to achieve desired mechanical properties. Using high-resolution scanning transmission electron microscopy, we here clarify the semi-coherent interfaces between the matrix and long-period stacking ordered (LPSO) phases, including 18R and 14H, in Mg–Zn–Y alloys. The LPSO/Mg interface features the unique configuration of the Shockley partial dislocations, which produces a near zero macroscopic strain because the net Burgers vectors equal zero. The 18R/Mg interface characterizes a dissociated structure that can be described as a narrow slab of 54R. There are two dislocation arrays accompanied to the 18R/54R and 54R/Mg interface, resulting a slight deviation (about 2.3°). The 14R/Mg interface exhibits the dislocation pairs associated with solute atoms. We further evaluate the stability and morphology of the corresponding interfaces based on elastic interaction, via calculating the mutual strong interactions between dislocation arrays, as well as that between the dislocations and solute atoms. The synchronized migration of interfacial dislocations and solute atoms, like move-drag behavior, dominates the lateral growth of LPSO phases in Mg alloys.