Copper–Palladium Phase Diagram

Phase equilibria in the copper–palladium system are extrapolated to absolute zero of temperature subject to the third law of thermodynamics. The continuous solid solution with a FCC structure that crystallizes from melt experiences ordering to yield two intermetallic phases (Kurnakov phases), whose compositions shrink to CuPd and Cu3Pd stoichiometries as temperature lowers. As temperature raises, palladium partially occupies copper sites in the intermetallic phases. Ordering obeying a second-order phase transition to yield a phase whose idealized composition may be formulated as Cu21Pd7. When in a solid state, the system forms an eutectoid at 390°C and 30 at % Pd and two dystectoids with coordinates of 510°C, 15 at % Pd and 600°C, 40 at % Pd.