Specific Features of Reactive Pulsed Laser Deposition of Solid Lubricating Nanocomposite Mo–S–C–H Thin-Film Coatings

Abstract

This work investigates the structure and chemical states of thin-film coatings obtained by pulsed laser codeposition of Mo and C in a reactive gas (H2S). The coatings were analysed for their prospective use as solid lubricating coatings for friction units operating in extreme conditions. Pulsed laser ablation of molybdenum and graphite targets was accompanied by the effective interaction of the deposited Mo and C layers with the reactive gas and the chemical states of Mo- and C-containing nanophases were interdependent. This had a negative effect on the tribological properties of Mo–S–C–H nanocomposite coatings obtained at H2S pressures of 9 and 18 Pa, which were optimal for obtaining MoS2 and MoS3 coatings, respectively. The best tribological properties were found for the Mo–S–C–H_5.5 coating formed at an H2S pressure of 5.5 Pa. At this pressure, the x = S/Mo ratio in the MoSx nanophase was slightly less than 2, and the a-C(S,H) nanophase contained ~8 at.% S and ~16 at.% H. The a-C(S,H) nanophase with this composition provided a low coefficient of friction (~0.03) at low ambient humidity and 22 °C. The nanophase composition in Mo–S–C–H_5.5 coating demonstrated fairly good antifriction properties and increased wear resistance even at −100 °C. For wet friction conditions, Mo–S–C–H nanocomposite coatings did not have significant advantages in reducing friction compared to the MoS2 and MoS3 coatings formed by reactive pulsed laser deposition.

Enhanced Tribological Performance of Low-Friction Nanocomposite WSexSy/NP-W Coatings Prepared by Reactive PLD

“…However, this view of the friction mechanism does not fully explain the tribological variability seen in TMD coatings of varying phases, their chemical composition, or architecture. As a result, there is continuing interest in investigating the ways to enhance the wear resistance of TMD coatings in a variety of conditions (such as medium composition and temperature) and to achieve ultralow friction [ 4 , 5 , 10 , 11 , 12 , 13 , 14 , 15 ].…”

Mechanism of tribo-induced structure modification for nanocomposite Mo-S-C-H thin film coatings

“…Mo−S−C−H coatings can differ significantly in properties from the currently actively studied coatings in Mo−S, Mo−S−C and a-C(H) systems created mainly by the method of ion-plasma deposition [9,10]. Thus, Mo−S−C−H coatings obtained in [8] overpassed in tribological properties the a-C(H) coatings when tested in humid air and inert gas at low temperatures. However, in the inert gas at room temperature the friction coefficient for the a-C(H) coating turned out to be the smallest, which is traditionally associated with hydrogen passivation of dangling bonds of carbon atoms.…”

“…Reactionary pulsed laser deposition (RPLD) makes it possible to flexibly control the composition and structure of coatings in the Mo−S−C system, as well as to implement hydrogen incorporation [8]. Mo−S−C−H coatings can differ significantly in properties from the currently actively studied coatings in Mo−S, Mo−S−C and a-C(H) systems created mainly by the method of ion-plasma deposition [9,10].…”

Laser Synthesis of Nanomaterials

“…The structure and chemical states of thin-film coatings obtained by pulsed laser co-deposition of Mo and C in a reactive gas (H 2 S) are investigated [ 9 ]. The performance of these coatings was analyzed for their prospective use as solid lubricating coatings for friction units operating in extreme conditions, showing that the nanophase composition in Mo–S–C–H_5.5 coatings has good antifriction properties and increased wear resistance, even at −100 °C.…”