Development of PGMs alloys suitable for the manufacture of jewelry

To address the limitations of pure palladium and its alloys in jewelry applications, particularly the insufficient hardness and poor castability, this study investigates novel alloying strategies using both noble and base metals. A minimum hardness of 150 Vickers is essential for wear-resistant jewelry, yet traditional palladium-platinum group metal (PGM) alloys fall short of this benchmark. Using CALPHAD and density functional theory (DFT) methods, the thermodynamic behaviour, phase stability, and mechanical properties of various Pd-based ternary and quaternary systems were analysed. The effects of alloying elements such as Ru, Al, Cu, Ga, and Co were explored in terms of hardness improvement, melting range modification, and structural behaviour. Results revealed that aluminium significantly broadens the melting range and enhances hardness through solid solution strengthening and precipitation. Ru, though limited in solubility, contributes to secondary phase formation and hardness enhancement. A compositionally optimized alloy, PdRu2255, was identified as a promising candidate that satisfies the mechanical, manufacturing, and regulatory requirements for high-quality jewelry applications.