About γ-brass phases in the Al-Cr-Fe system and their relationships to quasicrystals and approximants

We have identified two gamma-brass phases in the Al - Cr - Fe system by X-ray diffraction and transmission electron microscopy. These structures (rhombohedral and cubic) are closely related to each other and can co-exist in the same alloy together with approximants of quasicrystals. In particular, a long-period superlattice, typical of gamma-brass phases, was characterized in the cubic structure. This superstructure is constituted of inversion domains separated by boundaries lying at ((1) over bar 10) planes. The displacement vector between like domains was determined from high resolution microscopy data. This study deals also with a description of some structural links between gamma-brass phases and approximants of decagonal and icosahedral quasicrystals.