Synthesis, structure, and tribological behavior of nanocomposite DLC based thin films

Abstract

Diamond-like carbon (DLC) films possess a combination of attractive properties and have been largely employed to modify the tribological behavior of materials. Nanocomposite, metal-containing DLC films are the new generation of these coatings providing tremendous potential to modify and tailor their properties expanding their applications in the field of nanotechnology. The present study investigates nanoscale effects on the tribological behavior of composite nanostructured DLC-based films and functional coatings. Three aspects were studied: (i) effect of Cr interlayer on a functionally gradient substrate; (ii) nanoparticulate Cr-containing DLC (Cr-DLC) films; and (iii) nanocomposite multilayered Cr/DLC coatings. Intensified plasma assisted nitriding produced a functionally graded interface and Cr layers exhibited best tribological behavior in their presence validating the theoretical concept. Nanocomposite Cr-DLC films were synthesized with Cr content in the range of about 0.1 at% to about 17 at%, on Si100 substrate. TEM studies showed defect free, dense and continuous film containing crystalline nanoclusters embedded in amorphous matrix. X-ray absorption spectroscopy showed that the chemical state and environment around Cr in films with ¡Ý1.5 at% Cr is similar to that in Cr-carbide. However, the environment around Cr in films with Cr ¡Ü0.4 at% is distinctly different with atomic clusters of Cr dissolved in the DLC matrix. Nanoindentation experiments showed that Cr-DLC films possess high hardness. Also, Cr-DLC films exhibit low friction (up to 12 at% Cr) and excellent wear resistance (up to ~5 at% Cr) with a low stable wear rate (10-7 mm3/N-m). In the multilayered nanocomposite films, DLC layers were found to be amorphous whereas Cr layers exhibit a nanocrystalline structure. Cr/DLC interfaces were found to be dense and continuous. Presence of DLC and a decrease of Cr layer thickness increases the hardness. This behavior was found to be consistent with the Hall-Petch formalism. Multilayered nanocomposite films with a significant volume fraction of DLC were found to possess low friction and low wear rate (10-7mm3/N-m). A common wear mechanism was found on both nanocomposite and multilayered systems. These nanocomposite and multilayered systems exhibited wear and friction properties comparable to those of DLC films, thereby expanding their scope in the field of nanotechnology.