The Effect of Bilayer Periods and Their Thickness in Magnetron Sputtering Protective Multilayer Coatings for Tribological Applications

Abstract

CrN/CrAlN thin films were deposited by DC reactive magnetron sputtering. The influence of CrN/CrAlN bilayer thickness on the microstructure, mechanical, and tribological properties was studied. Crystallinity of the layers was characterized by x-ray diffraction. The microstructure of all coatings was observed by scanning electron microscopy. Results exhibit that bilayer thickness was a dominant factor. The analyses showed a columnar microstructure for the CrN/CrAlN coatings. Owing to their denser structure and interfacial strengthening, CrN/CrAlN multilayer coatings exhibited higher mechanical properties than that of monolayers. Indeed, CrN/CrAlN multilayer coating with four bilayers and thickness gradient reaches a maximum of hardness around 43 GPa. Also, its resistance to spallation reaches 97 N which is a very excellent value. After ball-on-disk wear tests, it is found that all multilayer films exhibited a good wear resistance, especially the one with four bilayers and different CrN and CrAlN monolayers thickness. The lowest coefficient of friction is obtained for the coatings with 4 bilayers.