Structure and ordering of the 18-carat Al–Au–Cu β-phase

Hardness and colour trends along the 76 wt.% Au (18.2 carat) line of the Au–Cu–Al system

“…The Au24%Cu-0% Al samples, which had the 1:1 stoichiometry of the AuCu-I phase, were relatively hard, but the hardness decreased rapidly on addition of Al. X-ray diffraction indicated that the Au-24%Cu samples were in fact partially ordered [11], which explained their relatively high hardness. However, even very small additions of Al evidently either retard the ordering kinetics of AuCu or depress its ordering temperature, or perhaps even induce solid solution softening, as is reportedly the case in in Cu 3 Au [12].…”

Determination of the 76 wt.% Au section of the Al–Au–Cu phase diagram

“…The structures of some of the less familiar phases were subsequently determined, and are reported elsewhere [9][10][11]. The degree of ordering of the AuCu-I phase was primarily determined by computation of the ratio a/c, determined for a four-atom fct (a/c>1) or bct unit cell (a/c<1).…”

Ternary β and γ phases in the Al–Au–Cu system at 750°C

“…These samples showed only the peaks expected for α-(Au,Cu) plus some evidence for a small proportion of a second phase, possibly the β-phase. Evidently, quenching suppressed the ordering reaction, as in the case of α-(Au,Cu)→AuCu [23]. The α-(Cu,Au,Al)→Cu 3 Au transformation occurred about 20˚C higher than that of a binary (Au,Cu) alloy of the corresponding Au:Cu ratio, indicating that the addition of 15 at% Al raised the ordering temperature.…”