Synergistic effects of electroless piston ring coatings and nano-additives in oil on the friction and wear of a piston ring/cylinder liner pair

To enhance the tribological performance of piston ring-cylinder liner pair in engines, Ni-P-TiN coated piston rings were prepared by electroless plating technology, and novel Fe₃O₄@MoS₂ nanocomposites were used as lubricating additives in oil. The tribological behavior of the coated friction pairs was evaluated on a multifunctional piston ring-cylinder liner tribometer. The results show that the concentration of TiN nanoparticles in the coatings has an important effect on the tribological performances. The coated piston ring-cylinder liner contact presented a mild abrasive wear with the concentration of TiN nanoparticles at 1.5 g/L. The coated piston rings did not increase the wear loss the cylinder liner due to the lubricating roles of TiN nanoparticles and the formation of transfer layer. The friction coefficient and wear loss of the Ni-P-1.5TiN coatings reduced by 23.8 ± 3.1 wt% and 64.3 ± 1.8 wt%, respectively, comparing to that of the Ni-P coating. Compared with nano-MoS₂ and nano-Fe₃O₄, the Fe₃O₄@MoS₂ nanocomposites as oil additives have a better effect on reducing the friction and wear of the Ni-P-TiN composite coating, mainly due to the synergistic effects of the coatings and the nanocomposite additives.