Investigation of chromaticity and mechanical properties of (Cu[sbnd]Ge) _100-xAl _x alloys with bimodal-sized intermetallic compound

The (Cu-Ge)100-xAlx alloys with different contents of Ge and Al solutes were designed to investigate the influence of solute elements on the microstructural evolution and chromatic and mechanical properties of the alloys. The addition of 0 -9 at% Al solute to the Cu97Ge3, Cu95Ge5, and Cu93Ge7 alloys led to microstructural evolution from a single-phase (alpha-Cu) to dual-phase structure consisting of alpha-Cu matrix and bimodal-sized zeta-Cu17Ge3 phase. The alloys with small amounts of Ge and Al have a single-phase structure or dual-phase structure with nanoscale zeta-Cu17Ge3 precipitates. An increase in Ge and Al solute induces the formation of a microscale interdendritic zeta-Cu17Ge3 phase with the alpha-Cu matrix, and the nanoscale Cu17Ge3 precipitates during solidification. The chromaticity (CIE a* and b* values) of the alloys is significantly influenced by the solute content as well as the microscale zeta-Cu17Ge3 phase. However, nanoscale zeta-Cu17Ge3 precipitates are ineffective in changing chromaticity. For the mechanical properties of alloys, the nanoscale zeta-Cu17Ge3 precipitates and microscale zeta-Cu17Ge3 phase contribute to improving the Vickers hardness via precipitation hardening and dispersion hardening effects. These results provide an effective way to expand the chromatic color range and improve the mechanical properties by developing dual-phase Cu-based alloys with a bimodal-sized second phase.