Re-investigation of phase equilibria in the system Al–Cu and structural analysis of the high-temperature phase η(1)-Al(1−δ)Cu

The phase equilibria and reaction temperatures in the system Al–Cu were re-investigated by a combination of optical microscopy, powder X-ray diffraction (XRD) at ambient and elevated temperature, differential thermal analysis (DTA) and scanning electron microscopy (SEM). A full description of the phase diagram is given. The phase equilibria and invariant reactions in the Cu-poor part of the phase diagram could be confirmed. The Cu-rich part shows some differences in phase equilibria and invariant reactions compared to the known phase diagram. A two phase field was found between the high temperature phase η(1) and the low temperature phase η(2) thus indicating a first order transition. In the ζ(1)/ζ(2) region of the phase diagram recent findings on the thermal stability could be widely confirmed. Contrary to previous results, the two phase field between δ and γ(1) is very narrow. The results of the current work indicate the absence of the high temperature β(0) phase as well as the absence of a two phase field between γ(1) and γ(0) suggesting a higher order transition between γ(1) and γ(0). The structure of γ(0) (I-43m, Cu(5)Zn(8)-type) was confirmed by means of high-temperature XRD. Powder XRD was also used to determine the structure of the high temperature phase η(1)-Al(1−δ)Cu. The phase is orthorhombic (space group Cmmm) and the lattice parameters are a = 4.1450(1) Å, b = 12.3004(4) Å and c = 8.720(1) Å; atomic coordinates are given.