Nano-mechanical and nano-tribological characterisation of self-lubricating MoS2 nano-structured coating for space applications

Tribological components cost only a fraction of the entire spacecraft, but they often lead to failures that partially or completely disrupt the spacecraft, resulting in a mission compromise. Mechanical components used in space applications have to withstand extreme environmental conditions, thus inhibiting the use of a liquid-based lubricant. Therefore, solid-based lubricating materials are employed for space applications. In this work, a PVD process was used to deposit a nano-structured coating of MoS2 on AMS 5898 stainless steel. The structure, morphology, and chemical composition were evaluated using X-Ray diffraction, FESEM, EDS, and Raman spectroscopy. The nano-tribological and nano-mechanical behaviour of the developed coating was investigated under various loads. Further, a ramp load nano-scratch test was also used to determine the adherence of the coating to the substrate. Results indicate that the MoS2 nano-structured coating has a polycrystalline structure with basal planes oriented perpendicular to the surface of the substrate. A substantial decrease in coefficient of friction was observed with an increase in applied load, while the wear rate showed an increasing trend with the applied load. A very low coefficient of friction of 0.02 and a low wear rate of 4.69 × 10−6 mm3/m were obtained during this study. The hardness and Young's modulus increased with an increase in the indentation load due to the reverse indentation size effect and substrate effect, respectively. The maximum values of hardness and Young's modulus were determined to be 9.46 GPa and 350.50 GPa, respectively. Furthermore, the coating adhered well to the substrate, with an adhesion strength of 1286.5 µN, and a coefficient of friction of 0.18 was reported during scratch testing.