Application of electron backscatter diffraction (EBSD) to quasicrystal-containing microstructures in the Mg-Cd-Yb system

We develop a new analysis system for identifying orientation of an icosahedral quasicrystal (iQc) in a SEM installed with an electron backscatter diffraction (EBSD) instrument. The system is successfully applied to determine the orientation of any given iQc grain by reading and assigning the Kikuchi bands obtained with the EBSD. This enables us to analyze relative orientations of iQc and αMg grains in a eutectic structure obtained through a unidirectional solidification process for the Mg-Cd-Yb system. According to EBSD analysis, growth direction of the eutectic structure is shown to be clearly parallel to a two-fold axis of the iQc and {10-10} of αMg, and a unique orientation relationship in iQc and αMg grains is verified in all iQc-αMg coexisting regions. The similarity between primary inter-planar spacings of the iQc and αMg phases is a key factor for stabilizing the interface of two phases and favoring the formation of eutectic structure. This stabilization mechanism is supported by a simple argument on the energetics of a quasiperiodic/periodic lattice interface.

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