2013 Volume 54 Issue 5 Pages 675-679
Plate-shaped precipitates accompanying change of chemical composition/order exhibit characteristics of displacive transformation when stacking sequence changes. One of intrinsic nature of long-period stacking ordered (LPSO) structures is, regular arrangements of stacking faults should cause significant change in local elastic strain field. This study intends to discuss problems of elastic strain in associated with LPSO structure and plastic accommodation processes by diffusion. It is indicated that required time for strain accommodation through boundary diffusion is negligibly small whereas that for volume diffusion is comparable to aging time where LPSO structure are formed via precipitation from the supersaturated Mg matrix. However, high degree of coherency between the fcc-base structural unit in the LPSO structure and Mg matrix, high-speed diffusion path for diffusional accommodation cannot be provided and thus, the volume diffusion controlled process or self-accommodation by combination of structural units with alternative shears should be dominant. The observation of 14H or 10H-type LPSO structure by aging clearly indicates such strain accommodation during sequence of precipitation.