Nickel concentration dependent mechanical and tribological properties of subsurface layer of electrodeposited Ni-C nanocomposite thin films.

• Mechanical properties of subsurface layer of films improve with nickel content. • Nickel incorporation increases the compactness and uniformity of composite films. • Subsurface layer of composite thin film shows enhanced tribological behaviour. • Frictional behaviour rely on chemical and structural properties of composite film. • Friction coefficient of films decreases with nickel which enhances the sp2 bonding. Electrodeposited nickel- carbon (Ni-C) nanocomposite thin films are found to have varying mechanical and tribological properties. Ni-C nanocomposites thin films of varying nickel content were synthesized by a simple electrodeposition method. Annealed thin films possess a relatively hard and adherent subsurface layer. In order to have an understanding of the mechanical and tribological characteristics of the subsurface layer, the relatively soft and fragile outer layer of the thin films was removed by scraping. The sp2 and sp3 bondings of carbon atoms in the thin films were explored by Raman spectroscopy. The Fourier- transform infrared spectra of the diamond-like carbon (DLC) and Ni-C thin films also consist of sp2 and sp3 hybridized carbon bonds. Nanocrystalline nickel nanoparticles distributed in carbon matrix were observed in Transmission electron microscopy study of the films. Decrease in coefficient of friction of the films is observed with increase in nickel content in thin films having DLC structure. The highest nickel content Ni-C composite thin film shows the maximum hardness of 7.6 GPa while the amorphous DLC thin film possesses the least hardness of 2.19 GPa. The subsurface layers demonstrate a clear demarcation of mechanical properties with unmodified overlayer pointing towards an extra care must be exercised before applying these electrodeposited coating on technological appliances. [ABSTRACT FROM AUTHOR]