Features of the disorder→order phase transition in non-stoichiometric Cu-56at%Au alloy

Abstract The evolution of the structure, electrical resistivity and microhardness of the non-stoichiometric Cu-56Au (at%) alloy during the disorder↔order phase transitions of samples with different thermo-mechanical histories has been studied. It was found that the rate of atomic ordering of the Cu-56Au alloy was much lower compared to the equiatomic Cu-50Au alloy that had been well studied earlier. It was shown that the deformation of the quenched alloy slowed down the rate of atomic ordering. It was established that annealing of the quenched alloy for 1 week at 250 °C led to the formation of the CuAuI phase with a degree of long-range atomic order S ≈ 0.8. The electrical resistivity of the alloy in this state is ρ = (7.75 ± 0.04) × 10 = (7.75 ± 0.04) × 10–8 Ωm, which is the lowest value known for this alloy. It was revealed that the ordered CuAuII phase forms as a result of annealing of the Cu-56Au alloy at high temperature followed by slow cooling to room temperature. During the experiments, we did not receive any data confirming the CuAuII→CuAuI transition both at heating and at cooling of the alloy. There was made a conclusion of a high thermal stability of the ordered orthorhombic CuAuII phase in the alloy under investigation.