CALPHAD coupled experimental investigation of structure–property evolution in solute lean Cu–Ni–Sn alloys

The transition towards low-Sn content alloy design represents a promising avenue for developing high-performance Cu–Ni–Sn alloys, enabling tailored microstructural evolution while minimizing the propensity for undesirable secondary phase formation. Accordingly, the present work presents a CALPHAD-coupled experimental investigation to elucidate the influence of Sn addition on microstructural characteristics and resulting properties of solute-lean Cu–Ni–Sn alloys. The alloys were synthesised using powder metallurgy route, wherein the Ni content was fixed at 4 wt%, while the Sn concentration was systematically varied from 0 to 4 wt%. The experimental findings closely corroborated the thermodynamic predictions, revealing that Sn additions up to 3 wt% preserve an FCC-dominated microstructure containing only a limited amount of solute-rich precipitates. Progressive enhancement in densification was observed with increasing Sn content from 0 to 3 wt%, where Cu–4Ni–3Sn alloy achieved the highest relative sintered density (~91%), corresponding to an improvement of ~11% over Cu–4Ni alloy. In contrast, further increasing the Sn content to 4 wt% resulted in reduced densification and a marked deterioration in electrical conductivity. Moreover, the compressive yield strength of Cu–4Ni–3Sn alloy exhibited more than two-fold increase relative to the Cu–4Ni alloy, with only marginal strengthening thereafter, indicating the onset of strength saturation with further Sn addition. Collectively, the findings obtained in this study demonstrate that judicious incorporation of 3 wt% Sn represents an effective solute-lean alloy design strategy for achieving a favourable combination of densification, strength and electrical conductivity in sintered Cu–Ni–Sn alloys.