Formation of long-period stacking fault structures in magnesium alloys

Abstract

We developed a Ginzburg-Landau model of long-period stacking order (LPSO) lamellar structure observed in magnesium alloys. Contrary to other models, we do not treat LPSO as a homogeneous stoichiometric phase but as a chemically modulated heterogeneous structure of parallel plates of two phases with different compositions and degrees of ordering. The Turing instability that is, existence of a finite-wavelength linear-instability mode was identified as the origin of formation of LPSO structure. The process of LPSO formation can be understood as a process of finding local minima and saddle points on the free energy landscape of the system. The model explained transformation between the two most common LPSO structures, 18R and 14H, and their general resistance to coarsening. The model can be used for the design of new LPSO materials.