Endothermic quasicrystalline-to-crystalline phase transition in Al₆CuMg₄

Abstract

Electron microscopic and differential scanning calorimetric (DSC) studies have been performed to investigate the phase transitions in the rapidly solidified Al₆CuMg₄ alloy system. We present evidence, for the first time, that anendothermic quasicrystalline to crystalline transition occurs in this system around 340° C. This is an unexpected feature-for conventional wisdom would lead one to expect exothermic behaviour as was seen in Al₈₆Mn₁₄-and points to the fact that stability of certain quasicrystalline phases may be much larger than hitherto expected. Some comments on the recently reported large quasicrystal for the Al₆CuLi₃ system are also made in the light of our observation.