Effects of Amorphous Formation by Si Addition on Microstructure, Mechanical and Tribological Properties for CrCoNiSi Film Fabricated by Magnetron Sputtering

The nitride films have been studied with Si addition due to improvement of hardness and wear resistance. High hardness of Si-containing nitride films such as TiSiN, NbSiN, and CrAlSiN has been achieved by the formation of nanocomposite structure due to the strong thermodynamic incompatibility between nitride metal and SiN_x. Some studies of nitride HEA film with Si addition to improve their hardness announce that no nanocomposite structure was observed by high mixing entropy effect which enhances the solubility of constituent element. In some Si-containing nitride HEA films showing high hardness, the amorphous regions were observed in the nanocrystalline state. Nevertheless, the formation of nanocomposites containing amorphous has not been revealed because it is difficult to verify phase segregation within the films due to the lack of component distribution differences. The CrCoNiSi alloy, which simultaneously improves strength and elongation through the Si addition, is expected to form an amorphous structure instead of Si compound in Si-containing HEA film by forming a single crystal structure up to Si 9.1 at%. In the literature, it was confirmed that the CrCoNi alloy, which is the basis of the CrCoNiSi alloy, has high hardness and excellent corrosion resistance through the hierarchical nanostructure in the thin film. In this study, we investigated the formation mechanism of amorphous and the resulting increase in hardness for Si-added the CrCoNi thin film. Here, CrCoNiSi thin films are used to study crystal structure deposited on Al alloy substrates by magnetron sputtering from the target fabricated via hot isostatic pressing. In the crystal structure of the deposited film, the amorphous appears with increasing Si content and the crystalline disappears in high Si content. As the amorphous was formed, the cell size of the thin film increased, and the surface porosity decreased by more than half on micro-scale, and the hardness increased greatly from 4.0 GPa to a maximum of 8.8 GPa. In a reciprocal sliding test of the CrCoNiSi film, enhancing hardness with increasing Si content occurs a reduction of friction coefficient and wear amount. The amorphous formation ability according to the alloy component causes a difference in amorphous formation, which affects the microstructure and the improvement of mechanical and tribological properties.