Combinatorial exploration of color in gold-based alloys

Combinatorial approaches comprised of combinatorial magnetron co-sputtering deposition and fast screening methods are introduced to study color as a function of composition in Au-based alloys. The microstructures of the thin films and bulk alloys are identified by X-ray diffraction, and their colors of the alloys are characterized by optical reflectivity. The results reveal that when comparing microstructures and reflectivity, thin films are similar to bulk alloys. In Au-Ag-Cu solid solutions, the color of the ternary alloy follows the rule of mixture. For colors resulting from Au[Al.sub.2] intermetallic, the color of an alloy scales with the percentage of the intermetallic phase and the deviation from its ideal binary composition. In the Au-Al-Cu library, we found a ~90% Au[Al.sub.2] area fraction compositional window where copper addition can be tuned to improve mechanical properties while keeping purple color, even though Al and Cu[Al.sub.2] phases exist. Moreover, when comparing the color in Au-Cu-Si-Ag amorphous and crystalline state solid solution for the same composition, the colors are essentially identical. Keywords Gold alloys * Microstructure * Amorphous alloys * Intermetallics * Solid solution * Decorative thin film coating
Introduction Color is ubiquitous and plays an important role in our daily life [1]. Although there are various mechanisms underlying the generation of color, for gold(Au) and copper(Cu), it is [...]