Investigation of chromaticity and mechanical properties of (CuGe)100-xAlx alloys with bimodal-sized intermetallic compound

The (CuGe)_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 Cu₉₇Ge₃, Cu₉₅Ge₅, and Cu₉₃Ge₇ alloys led to microstructural evolution from a single-phase (α-Cu) to dual-phase structure consisting of α-Cu matrix and bimodal-sized ζ-Cu₁₇Ge₃ phase. The alloys with small amounts of Ge and Al have a single-phase structure or dual-phase structure with nanoscale ζCu₁₇Ge₃ precipitates. An increase in Ge and Al solute induces the formation of a microscale interdendritic ζCu₁₇Ge₃ phase with the α-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 ζ-Cu₁₇Ge₃ phase. However, nanoscale ζ-Cu₁₇Ge₃ precipitates are ineffective in changing chromaticity. For the mechanical properties of alloys, the nanoscale ζ-Cu₁₇Ge₃ precipitates and microscale ζ-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.