On the constitution of the high-Al region of the Al–Cr alloy system

The compositional range of the Al–Cr alloy system above 75 at.% Al was investigated by powder X-ray diffractometry, differential thermal analysis, scanning and transmission electron microscopy. A hexagonal phase isostructural to μ-Al4Mn (a ≈ 2.00 nm, c ≈ 2.47 nm) was found to be formed in a compositional range from about 78.7 to 81.3 at.% Al. A higher-Al Al11Cr2 phase was associated with the C-centered monoclinic (pseudo-orthorhombic) structure with a ≈ 1.76 nm, b ≈ 3.05 nm, c ≈ 1.76 nm and β ≈ 90° reported earlier. No orthorhombic structure with a ≈ 3.46 nm, b ≈ 2.00 nm, c ≈ 1.24 nm related in the literature to either Al45Cr7, Al11Cr2 or Al4Cr was revealed at all. The peritectic temperature of the Al11Cr2 phase formation was found to be ∼865 °C and the stability of this phase was confirmed down to 600 °C.