Re-investigation of phase equilibria in the system Al–Cu and structural analysis of the high-temperature phase η1-Al1−δCu

AbstractThe 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 η1 and the low temperature phase η2 thus indicating a first order transition. In the ζ1/ζ2 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 γ1 is very narrow. The results of the current work indicate the absence of the high temperature β0 phase as well as the absence of a two phase field between γ1 and γ0 suggesting a higher order transition between γ1 and γ0. The structure of γ0 (I-43m, Cu5Zn8-type) was confirmed by means of high-temperature XRD. Powder XRD was also used to determine the structure of the high temperature phase η1-Al1−δCu. 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