Modulated structure of Laves phase in a cast Mg-Zn-RE alloy

Abstract

Comparison of the two SAED patterns (Fig.l) obtained from Laves phase in Mg-9Zn and Mg- 8Zn-1.5RE (RE: rare earth additions made by adding misch metal), shows that the small amount of rare earth additions has a considerble influence on the crystal structure of this phase. The diffraction features suggest that the crystal structure of the Laves phase in the Mg-Zn-RE alloy is modulated by planar translation interfaces which are equivalent to a uniform sequence of antiphase boundaries (APBs) in a long period superstructure. From the splitting distance of the superlattice spots as illustrated in the schematic diagram in Fig. 1(c), the mean half period, which is measured in units of (100) interplanar spacings, is M ≈ 4.86. As shown by Van Dyck et al. the superstructure reflections (or the satellites of the basic spots) of a periodic APB structure are peaked at positions given by: g' = g - (1/d)(m - g.R),