Investigation of the Tribofilm Formation of HiPIMS Sputtered MoSx Thin Films in Different Environments by Raman Scattering

Abstract

Understanding the generation of third body particles and their contribution to the formation of tribofilms of MoS x thin films is still challenging due to a large number of influencing factors. Besides the structure of the as-deposited MoS x films, the environment and the conditions during the Ball-on-disk tests affect tribofilms and thus the friction. Therefore, the influence of the surface pressure and sliding velocity in air, argon and nitrogen environments on the generation of the third body particles and the tribofilm formation of randomly oriented MoS x films is investigated. A high surface pressure is one major factor to achieve low friction, especially under humid conditions, which is important considering the use in industrial applications, for example dry-running screw machines. However, the mechanisms leading to that frictional behavior are still affected by the surrounding environment. While low friction is caused by a more extensive tribofilm formation in air, in argon and nitrogen, large size third body particles dispensed all over the contact area contribute to a lower friction. Raman scattering reveal a different chemistry of these particles reflected in the absence of laser-or temperature-induced surface oxidation compared to the as-deposited film and the wear track. The Raman scattering results are discussed with respect to the wear particle size, its chemical reactivity and strain-induced bonding changes.

Wear and Rolling Contact Fatigue Analysis of AISI 52100 Bearing Steel in Presence of Additivated Lubricants

“…However, in case of MoS 2 and PT, apart from the deposition of the additives, several other peaks were also observed, especially iron oxides. The Raman spectra at 287 cm −1 , 360 cm −1 , 391 cm −1 , 416 cm −1 and 473 cm −1 are quite close to the Raman spectra of MoS 2 as reported by Tillman et al [23], indicating the deposition of MoS 2 on the wear tracks. In addition, weak spectra of molybdenum oxides (MoO 2 ) was also detected at 744 cm −1 [24].…”

Structure and Tribo-Mechanical Properties of MoSx:N:Mo Thin Films Synthesized by Reactive dcMS/HiPIMS

“…This indicates the dynamic interaction of the generated film material. The generated film particles participate during the sliding process and are just removed from the contact area after both contact partners are separated as discussed in previous investigations (Ref 20,46). Due to the incorporation of a low amount of additional Mo, the amount of the film material contributing the lubricating effect is increased, since the breakup of the columns is complicated (Ref 47).…”

Controlling the Structural, Mechanical and Frictional Properties of MoSx Coatings by High-Power Impulse Magnetron Sputtering

“…S/Mo ratios between 0.8 and 1.5 are obtained for bipolar pulsed magnetron sputtered MoSx thin films [45]. According to reference [16], an increasing bias-voltage results in a reduction of the S/Mo ratio due to resputtering and an enhanced ion bombardment. These effects are most likely to be found in the resputtering of sulfur since it has a lower atomic mass than molybdenum.…”

“…A low coefficient of friction and an extended lifetime shall be achieved by combining a good adhesion of the surface layer to the substrate, a high purity of the coating, and a dense morphology with a small crystallite size [15]. For a HiPIMS grown MoS x thin film, a decrease of the friction coefficient is reported with an enhanced surface pressure applied during the tribological contact, due to the formation of more third-body particles leading to a thicker tribofilm formation [16]. A transfer film formation is also promoted by oxygen and H 2 O in the atmosphere as reported by Li et al [17].…”