Lighter and more powerful next generation vehicles and other rotary machinery demand bearings to operate in harsher conditions for higher efficiency, and the continuous development of advanced low-wear and friction materials is thus becoming even more important to meet these requirements. New aluminium composites reinforced with high performance lubricate phases such as graphene nanoplatelets (GNPs) are very promising and have been vigorously investigated. By maintaining a low coefficient of friction (COF) and offering great strength against wear due to their self-lubricating capability, the solid lubricant like GNPs protect the bearing surface from wear damage and prevent change in metallurgical properties during temperature fluctuations. This paper first studies the high-temperature tribological performance of aluminium matrix composites reinforced with GNP, consolidated via powder metallurgy, then elucidates their tribological mechanism. We report that the best tribological performance is achieved by the composite containing 2.0 wt% GNP, with an extraordinarily low COF of 0.09 and a specific wear rate of 3.5×10^-2 mm³∙N^-1∙m^-1, which represent 75% and 40% reduction respectively, against the plain aluminium consolidated under identical conditions. The in-track and out-of-track Raman analysis have confirmed the role of GNPs in creating a tribofilm on the counterpart surface which contributed to the excellent performance.

The present study is focused on the evaluation of the tribological performance of novel Ni/hBN and Ni/WS₂ composite coatings electrodeposited from an additive-free Watts bath with the assistance of ultrasound. Lubricated and non-lubricated scratch tests were performed on both novel composite coatings and on standard Ni deposits used as a benchmark coating to have an initial idea of the effect of the presence of particles within the Ni matrix. Under lubricated conditions, the performance of the Ni/hBN composite coating was very similar to the benchmark Ni coating, whereas the Ni/WS₂ behaved quite differently, as the latter did not only show a lower coefficient of friction, but also prevented the occurrence of stick-slip motion that was clearly observed in the other coatings. Under non-lubricated conditions, whereas the tribological performance of the Ni/hBN composite coating was again very similar to that of the benchmark Ni coating, the Ni/WS₂ composite coatings again showed a remarkable enhancement, as the incorporation of the WS₂ particles into the Ni coating not only resulted in a lower coefficient of friction, but also in the prevention of coating failure.