Influence of Cr addition on chromaticity and mechanical properties of solid solution Cu-Ni-Cr alloys with dual-phase structure based on liquid phase separation

Cu-Ni alloys are versatile materials for various industrial and engineering applications, known for their ability to maintain strength and ductility while possessing desirable chromatic properties. We focused on synthesizing a ductile solid solution of Cu-Ni alloy and incorporating Cr element to modulate chromaticity and to enhance mechanical properties. The influence of Cr content on the microstructure, chromaticity, and mechanical properties of (Cu85Ni15)(100-x)Cr-x alloys was systematically investigated. Microstructural analysis confirmed that phase separation of FCC alpha-Cu and BCC alpha-Cr solid solution phases occurred with increasing Cr content, and the size and morphology of alpha-Cr phase depended on the Cr content. The color difference of alloys evaluated using reflectivity analysis on the CIE L*a*b* color space system confirmed that there was a distinct color difference and the reflectivity, which significantly depended on Cr content and phase separation. The fine and coarse alpha-Cr phases contributed to color variation and improved hardness. The Vickers hardness of these alloys was significantly improved from 73 HV to 113 HV. Moreover, the yield strength and ultimate tensile strength also improved while maintaining large plasticity (similar to 34 %) and high work-hardenability with an increasing volume fraction of alpha-Cr phase. This study highlights the feasibility of designing Cu-based color alloys with expanded chromaticity and improved mechanical properties, offering valuable strategies for applications demanding specific color and material characteristics.