Multilayer Coatings Based on van der Waals MoS2/WS2/WSe2 Heterostructures with Improved Antifriction Properties

Multilayer coatings consisting of nanocrystals with layered atomic packing, in which planes with dense atomic packing are combined into a crystal through weak van der Waals interaction, were created by alternating pulsed laser ablation of MoS2 and WSe2 targets in vacuum conditions. Deposition on a substrate heated to 400°C caused both the crystallization of the layers and the formation of the WS2 phase at the layer interfaces. As a result of the peculiarities of pulsed laser ablation of the selected targets, the van der Waals matrix of the layers contained metal nanoinclusions (bcc-Mo and β-W). The tribological properties were studied by sliding a steel ball over the coating at low relative humidity. The coefficient of sliding friction decreased with increasing load on the counterbody down to an ultralow value of 0.01. The friction caused some disordering of the crystalline structure of the layers and mass transfer in the contact area of the coating. The low value of the friction coefficient could be due to the difference in the packing parameters of atoms in the basal planes of molybdenum and tungsten dichalcogenides, accumulating in the tribofilm and determining the shear stresses of the atomic layers at local interfaces during counterbody sliding. Metallic nanoparticles could influence the tribo-activated modification of the nanostructure and the composition of the coating in the tribofilm.