Metastability matters: Exploring hardness and conductivity in bell bronze alloys

The Cu-Sn alloy system exhibits diverse stable and metastable phases with complex phase transformations, making it attractive for applications requiring tailored mechanical and electrical performance. This study investigates the mechanical response of individual phases during ongoing phase transformations in a Cu-20 m.% Sn alloy. Heat treatments produced large-grained microstructures containing distinct phase combinations in equilibrium and non-equilibrium states. The evolving microstructure was characterized using light optical and scanning electron microscopy. Phase-specific hardness, Young’s modulus, and strain rate sensitivity were determined through room-temperature and high-temperature nanoindentation combined with electron back-scattered diffraction phase mapping, alongside compression testing. This method enables direct quantification of phase properties under phase transformation, separating the contributions of stable and metastable phases. Results reveal how transformation kinetics and solute interactions govern the phase-specific deformation bulk performance, offering new insights into structure–property relationships in Cu-Sn alloys. The methodology provides a framework for phase-specific property characterization in transforming systems, supporting the design of materials with transformation-informed properties optimization.