Paper AS+BI-TuA11
Study of Quasicrystal / α - Mg Eutectic Structure in the Mg-Cd-Yb System by EBSD

Tuesday, October 29, 2013, 5:20 pm, Room 204

A pseudo-binary phase diagram composed of iQc (icosahedral quasicrystal) and α-Mg in Mg-Cd-Yb system reveals a eutectic reaction at Mg₆₈Cd₂₄Yb₈. The alloy with eutectic composition prepared by slow cooling shows irregular eutectic structure of QC and α phases. In terms of interface stability, the iQc / α interfaces are realized to be most stable since eutectic structure contains largest area of interface. This study is aiming at understanding an essential question; “how does a quasiperiodic lattice match a periodic lattice ?” The other challenging topic is the application of EBSD (Electron Back Scattering Diffraction) for the first time to study microstructure of a quasicrystalline material.

In X-ray diffraction patterns, a number of main peaks of iQc coincide with those of α phase, indicating good lattice matches between two phases. For examples, basal plane and prismatic plane of α phase have the similar lattice spacing to 2-fold symmetry plane and 5-fold symmetry plane, respectively. EBSD analysis revealed that the growth direction of iQc-α eutectic is ,,2f .-iQc. // ,,1 0 ,1. 0 .-Mg. and a number of orientation relationships between QC and α phase have been verified. Furthermore, a number of directions normal to the planes of iQc coincide to those normal to the planes having similar lattice spacing of iQc in the α phase. The interface stability is likely due to good lattice matches between iQc and α phase.