Tribological Investigation of Composite MoS2-TiO2-ZrO2 Coating Material by Response Surface Methodology Approach

Molybdenum disulphide (MoS2) is popularly used in tribological applications because of its excellent lubricating properties. However, its performance needs to further improve. In the present study, an attempt has been made to improve the wear resistance of pure MoS2 coating by incorporating TiO2 and ZrO2 nanoparticles as a reinforcement material into the MoS2 base matrix. The composite MoS2-TiO2-ZrO2 coating was applied onto substrate surface by bonding technique. The tribological performance of the coated specimens was evaluated employing various operating conditions (such as wt. % of compounding elements, contact pressure, sliding speed) using pin-on-disc friction and wear test rig. A statistical model was developed to identify the significant factors affecting the friction coefficient (COF) and wear rate of the composite coating material. The design of experiment (DOE) were formulated by response surface methodology (RSM) approach to cut down the number of experiments and to develop a mathematical model between the key process parameters such as wt. % of compounding elements, contact pressures, sliding speeds. Analysis of variance (ANOVA) test was executed for checking the adequacy of the empirical models developed. It was discovered that the COF and wear rate of composite MoS2-TiO2-ZrO2 coating significantly affected by the wt. % addition of ZrO2. The SEM and optical microscopy analyses of the worn surfaces and transfer films indicated that the tribological properties of composite MoS2-TiO2-ZrO2 coating were significantly improved compared to pure MoS2 coating.

Effects of Aviation Lubrication on Tribological Performances of Graphene/MoS2 Composite Coating

Four kinds of aviation liquid lubricants (i.e., 4010#, 4050#, 4106#, and 4109# oils) were homogeneously coated on the graphene/MoS2 composite coating through a spin-coating method to form the solid–liquid lubricating combinations. The tribological properties of the obtained solid–liquid combinations and pure graphene/MoS2 coating were investigated experimentally. Effects of the liquid lubricant type on the friction and wear behaviors of the solid–liquid combinations and pure graphene/MoS2 coating were studied at different applied loads and rotational speeds. Within the ranges of the applied load varying from 10 to 50 N and rotational speed varying from 750 to 1500 rpm, the presence of the above-mentioned liquid lubricants significantly reduces the friction coefficient of the pure graphene/MoS2 coating, and the reduction rate is as high as 24%. Additionally, the coating-4109# combination has the best synergistic effect under the above operation condition.

Reactive Pulsed Laser Deposition of Clustered-Type MoSx (x ~ 2, 3, and 4) Films and Their Solid Lubricant Properties at Low Temperature

We studied the tribological properties of amorphous molybdenum sulfide (MoSx) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (−100 °C). To obtain films with different sulfur contents (x ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H2S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS3 coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS2 coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS2 coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS4 coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoSx coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoSx films.

Effect of Zr Target Current on the Mechanical and Tribological Performance of MoS2–Zr Composite Lubricating Coatings

To improve the tribological properties of pure MoS2 coating, the MoS2–Zr composite lubricating coatings were prepared on the WC/TiC/Co carbide surface utilizing radio frequency magnetron sputtering method combining with multiple arc ion plating technology. The effects of different Zr target currents on the surface morphologies, roughness, Zr content, adhesive force, thickness, microhardness and tribological behaviors of the composite coatings were systematically investigated. Results showed that the properties of MoS2 coating can be remarkably enhanced through co-deposition of a certain amount of Zr. As the Zr target current increased, the Zr content, surface roughness, thickness, and micro-hardness gradually increased, while the adhesive force of coatings increased first and then decreased. The friction behaviors and wear modes of the composite coatings both varied obviously with the increase of Zr current. The mechanism was mainly attributed to the different components and mechanical properties of the coatings caused by various Zr current.