Crystallographic orientations and interfaces of icosahedral quasicrystalline phase growing on cubic W phase in Mg-Zn-Y alloys

Formation of icosahedral quasicrystalline phase on the W cubic phase in α-Mg matrix has been studied in a Mg₉₇Zn_2.5 Y_0.5 alloy. The orientation relationship of the W phase with the matrix is determined to be [0 0 1]_W ∥[1 0 0]_Mg, (1 1 0)_W∥ (0 0 1)_Mg, equivalent to Burgers orientation relationship. The icosahedral phase forms curved interfaces with the W phase, but planar interfaces on five-fold and two-fold planes with the matrix. The icosahedral phase shows its unique orientation relationship to the W phase, which results in two orientation relationships WOR1 and WOR2 with the matrix. WOR1 is a slight deviation of the orientation relation, OR1, of icosahedral phase precipitates in the matrix. In WOR2, one of the five-fold axes occur along the hexagonal axis. The resulting morphology and the interface structures are described here. It is shown that WOR1 and WOR2 are related to each other by twinning of the icosahedral phase.