Effect of Load on Tribological Behavior of MoS₂/C Composite Films

MoS₂/C composite films with Ti interlayer were prepared by direct current magnetron sputtering and high power impulse magnetron sputtering, and the structure, composition and mechanical properties were characterized. The tribological tests were carried out on a ball-on-disc tribometer, and results show that the friction coefficient and the wear rate decreased regularly with an increasing load. The average friction coefficient was analyzed and fitted by Hertzian contact model, combined with the wear tracks and wear scars observed by scanning electron microscopy. It is found that the change in load resulted in a difference of the Hertzian contact area and the Hertzian contact pressure, which led to the change of the friction coefficient. Wear products detected by Raman spectroscopy showed that different loads did not cause the different graphitization degree of amorphous carbon. Microstructure of the transfer film analyzed by transmission electron microscopy showed that the transfer film was finely-aligned MoS₂ with basal plane in parallel to the shearing direction, which had a lower shear strength at higher loads and thus resulted in a low coefficient of friction. Based on the results of the experimental verification with the loads varied from high to low in the same tribological conditions, it can be concluded Hertzian contact accounted for a low coefficient of friction at high loads.