Use of Resistometry for Locating the Temperature–Composition Boundary of the L12 → A1 Phase Transformation in Cu–Pd Alloys

Resumo

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 (t_c) in the Cu–8 at % Pd alloy is ~380°C, and that in the Cu–5.9 at % Pd alloy is t_c ≈ 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.