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

The (Cu[sbnd]Ge) 100-xAl x 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 Cu 97Ge 3, Cu 95Ge 5, and Cu 93Ge 7 alloys led to microstructural evolution from a single-phase (α-Cu) to dual-phase structure consisting of α-Cu matrix and bimodal-sized ζ-Cu 17Ge 3 phase. The alloys with small amounts of Ge and Al have a single-phase structure or dual-phase structure with nanoscale ζ[sbnd]Cu 17Ge 3 precipitates. An increase in Ge and Al solute induces the formation of a microscale interdendritic ζ[sbnd]Cu 17Ge 3 phase with the α-Cu matrix, and the nanoscale Cu 17Ge 3 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 ζ-Cu 17Ge 3 phase. However, nanoscale ζ-Cu 17Ge 3 precipitates are ineffective in changing chromaticity. For the mechanical properties of alloys, the nanoscale ζ-Cu 17Ge 3 precipitates and microscale ζ-Cu 17Ge 3 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.