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

The (Cu Ge) 100-x Al 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 97 Ge 3 , Cu 95 Ge 5 , and Cu 93 Ge 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 17 Ge 3 phase. The alloys with small amounts of Ge and Al have a single-phase structure or dual-phase structure with nanoscale ζ Cu 17 Ge 3 precipitates. An increase in Ge and Al solute induces the formation of a microscale interdendritic ζ Cu 17 Ge 3 phase with the α-Cu matrix, and the nanoscale Cu 17 Ge 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 17 Ge 3 phase. However, nanoscale ζ-Cu 17 Ge 3 precipitates are ineffective in changing chromaticity. For the mechanical properties of alloys, the nanoscale ζ-Cu 17 Ge 3 precipitates and microscale ζ-Cu 17 Ge 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. • Addition of Al content on Cu-Ge alloy introduces bimodal-sized ζ-Cu 17 Ge 3 phase in α-Cu matrix. • Nanoscale and microscale ζ-Cu 17 Ge 3 phase have different roles in chromaticity and mechanical properties. • Chromaticity of alloys is significantly influenced by Al and Ge content and formation of microscale ζ-Cu 17 Ge 3 phase. • Nanoscale ζ-Cu 17 Ge 3 precipitates improve the hardness by precipitation hardening effect. • Microscale ζ-Cu 17 Ge 3 phase also contributes to enhance the hardness by dispersion hardening effect.