Quasicrystals and Approximant Crystals subjected to the Mechanical Alloying in the Mg-Al-Pd Alloy System

Abstract

Mg-based quasicrystals possessing the rhombic triacontahedron (RT) cluster as a structural unit have been prepared through the mechanical alloying (MA) process. The MA process is efficient in searching for the formation area of the icosahedral quasicrystalline phase of the RT type (IRT-phase), because it forms directly from the crystalline elemental powders within a few hours through the solid state reaction. In the previous study, the formation area of the thermally stable IRT-phase and related approximant phases had been determined in the Mg-Al-Zn system. In this study, we have determined the formation area of the IRT-and 1/1 approximant phase in the Mg-Al-Pd system as in the Mg-Al-Zn system. The formation areas and the thermal stability of the IRT-and the 1/1 approximant phases in the Mg-Al-Pd system have been compared to those in the Mg-Al-Zn system. We concluded that both Mg concentration and an average number of sp-valence electron per atom play a critical role in determining the formation area of the thermally stable IRT-and 1/1-phases both in the Mg-Al-Pd and the Mg-Al-Zn systems.