Influence of Microstructure, Composition and Morphology on Tribological Performance of WTiN Coatings Obtained by DC Magnetron Sputtering at Various Working Pressures

Abstract

In this work, WTiN thin films were produced on silicon substrates using the DC magnetron sputtering technique varying the working pressure and keeping the power constant at 90 W and conducting the process at room temperature. The structure and morphology of the coatings were analyzed using the x-ray diffraction technique, which allowed the identification of a rock salt type FCC structure, with a relatively low micro-strain, and a grain size in the order of nm exhibiting a nanostructure formation. Elemental composition and the binding energies of samples were obtained using x-ray photoelectron spectroscopy and showed W-Ti-N chemical bonds and hence the formation of the ternary nitride. Moreover, a great influence of the pressure on the stoichiometry was identified, as a result of the differences in the deceleration and diffusion behavior of W and Ti atoms. The surface grain size and roughness (on average approximately 34 and 8.7 nm, respectively) of the coatings were determined using atomic force microscopy. Changes in the morphology can be attributed to re-sputtering and the adatoms mobility processes, as a part of the growth mechanism. Finally, for determining the tribological behavior, scratch and pin on disk tests were conducted. According to the results, the roughness and the pressure had a great influence on the coefficient of friction and the wear rate; however, the working pressure had no significant influence on the adherence of the films.