A comparative study of surface morphology, mechanical and tribological properties of DLC films deposited on Cr and Ni nanolayers

Applying metallic interlayer between diamond-like carbon (DLC) and substrate is a promising method to improve the adhesion and efficiency of DLC films. Understanding how the interlayer parameters affect the properties of DLC coatings leads to production of long-time excellent performance of them. In this study, DLC films deposited by PECVD and 10, 20 and 40 nm layers of Ni and Cr were sputtered on silicon substrates to use as the adhesion layers. The role of chemical structure and physical parameters (surface roughness) of interlayers on the final properties of DLC films were investigated using atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoscratch and nanoindentation techniques. It was found that a lower surface roughness with a sharp and homogenous distribution of particles sizes (height) results in formation of a smooth DLC film with lower friction coefficient, more stress reduction and better adhesion strength. It was discussed that the chemical structure of the interlayer was important in the solubility and diffusion of carbon atoms and consequently in instability of sp3 and sp2 bonding. Results demonstrated that 40 nm Cr interlayer, not only improved the adhesion of the DLC films but also generated the lowest friction coefficient, better wear resistance and the highest hardness (27 GPa).