Effects of oxygen addition on properties of an amorphous Co–Ta–B system

Generally, amorphous alloys with metallic luster are mechanically strong and tough, whereas they are optically opaque. In contrast, amorphous metal oxides are optically transparent, whereas they show very low fracture toughness due to their intrinsic brittleness. Introducing oxygen into amorphous alloys enables formation of multifunctional amorphous materials, which combine high strength of amorphous alloys and optical properties of amorphous metal oxides. Using this strategy, a series of amorphous thin films were developed via oxygen manipulation in an amorphous Co–Ta–B system. The effects of oxygen addition on the optical properties of the amorphous Co–Ta–B–O thin films have been investigated systematically. Optical transmittance of these thin films increases with increasing the oxygen content. Integrating the transparent Co23·17Ta9·20B16·94O50.69 thin film with Si substrate forms a bilayer structure to display various colors via a simple thin film interference effect. In addition to the optical properties, the Co24·37Ta6·96B24·99O43.69 thin film with dual-phase nanostructure show a combination of high hardness of ∼7.49 GPa and a high H/E ratio of 0.062, representing good wear resistance. Our results offer a simple means to produce mechanically strong amorphous thin films with attractive optical properties, which show potential as advanced surface coatings to meet the requirements for high hardness and decorative appearance.