Use of Resistometry for Locating the Temperature–Composition Boundary of the L 1 2 → A 1 Phase Transformation in Cu–Pd Alloys

The resistivity of low-palladium copper-based FCC solid solutions has been measured as a function of temperature during heating and cooling. We have compared the electrical properties of pure copper and those of the Cu–8 at % Pd alloy, which can undergo L12 ordering, after similar heat treatments. The anomalies found in the Cu–5.9 at % Pd alloy have been interpreted in terms of the formation of nuclei of an L12 ordered phase, in contrast to the generally accepted Cu–Pd phase diagram. The resistometry data indicate that the temperatures of the order → disorder phase transformation (tc) in the Cu–8 at % Pd alloy is ~380°C, and that in the Cu–5.9 at % Pd alloy is tc ≈ 350°C. The experimental data obtained are compared to first principles calculation results on the stability of the L12 phase in the Cu–Pd binary alloys.