Investigation of the Al-Cr γ-range

The range of Al-Cr between 25 and 50 at.% Cr was reinvestigated by powder X-ray diffractometry, differential thermal analysis, scanning and transmission electron microscopy. Experiments point to the existence of only one high-temperature and one low-temperature phase extending in the compositional range between about 30 and 42 at.% Cr. The low-temperature phase (γ2) has a rhombohedrally distorted γ-brass structure with α < 90° continuously varying with the composition. This phase exhibited twin-oriented domains, which, in turn, consisted of the second-order twins. At 36 at.% Cr and below very fine and periodically arranged stripes were formed, which resulted in additional reflections in the corresponding electron diffraction patterns.