A planar growth with a growth direction parallel to a 5-fold symmetrical axis was found in a melt-quenched Al72Pd25Cr3 icosahedral alloy. An interpretation is given on the basis of a stability criterion that the plane perpendicular to the 5-fold axis is that of stable growth in an icosahedral phase (i-phase) and the solid-liquid interface instability occurs during solidification. It leads to the formation of cellular growth along the 5-fold axis and dendritic morphology. We find that decagonal phase (D-phase) grains nucleate from the i-phase and grow with the relationship that one of the 5- fold directions of the i-phase which have an angle of 63.43° between each other coincides with the 10-fold direction of the D-phase.
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