抄録
Studies of approximant crystals have been regarded as playing an important role to deepen the understanding of the quasicrystals. By making use of the fact that mechanical milling (MM ) technique can produce an icosahedral quasi crystalline (QC) phase over the composition range where the cubic 1/1-approximant phase is stable in the Mg-Al-Zn system, we have studied the transformation process from the 1/1-approximant to the quasicrystal by MM and vice versa by the heat treatment. The 1/1-approximant or the so called Frank Kasper Mg39.5Al20Zn40.5 alloy was used as a starting material. We revealed that the transformation into the QC accompanies the reduction in the lattice constant a1/1 of the approximant, while the initially grown QC has the quasilattice constant aR larger than the value eventually reached, which agreed with the calculated value from the a1/1 of the starting approximant. The reverse process is observed in the heat treatment mode. We conclude that the composition partitioning is induced by milling and also by the heat treatment and is responsible for the preferential growth of the Mg-rich thermally stable QC and the reduction in the a1/1 value of the approximant in the MM process.
