An-Pang Tsai

Abstract:

We have developed a new analysis system for identifying the orientation of icosahedral quasicrystal (iQc) in a SEM installed with an electron back scattering diffraction (EBSD) instrument. The system has been successful in assigning the orientations of the iQc and a ��Mg phases in a eutectic structure prepared by a unidirectional solidification process at a different cooling rate in the Mg-Cd-Yb system. A regular rod-like microstructure was observed in wide regions, where inter-rod spacing decreases with increasing solidification rate. Significant contributions of unidirectional solidification on microstructure were confirmed. It is clear that basal plane of Mg and 2-fold symmetry plane of QC reveal the similar lattice spacing. Also, the prismatic plane of Mg and 5-fold symmetry plane of iQC have the similar lattice spacing. According to EBSD result, the growth direction of iQC/Mg eutectic structure is �q 2f �r_QC // �q 1 0 1 ̅ 0 �r_Mg and a unique orientation relationships between iQC and Mg have been verified. The similar lattice spacing with planar normal along growth direction is a key factor stabilizing the interface of iQC and Mg. In the unidirectional solidification samples, the eutectic growth of iQC/Mg is analyzed to be a non-facet/non-facet mode.