The structure and tribological properties of Ni/MoS2 composite layers formed on aluminum and its alloys

Abstract

This work investigates the influence of process parameters on microstructure, adhesion of layers to the substrate and wear resistance of Ni/MoS2 micro- and nanocrystalline composite layers. Pure nickel coatings were also fabricated and tested for comparison. The layers were deposited by electrochemical reduction on pure A2 aluminum and on PA6 alloy. The layers were produced at a current density of 3 A/dm2 and a mixing speed of 400 rpm. The bath composition was also modified by the addition of saccharin and the disperse phase of molybdenum disulfide in the bath (2.5 and 5 g/l). Materials prepared in this way underwent structural investigations (using scanning electron microscopy and optical microscopy), a scratch test and tribological tests (using a ball-on-disc method). The results of the tests allowed to determine the dependence of the structure and properties of the produced coatings on the production parameters. The composition of the electrolyte affects the size of crystallites as well as the morphology and topography of the surface. The scratch test confirmed the good adhesion of the nickel and composite layers to the substrate. The best lubricating properties were shown by nanocrystalline coatings. The too high content of molybdenum disulfide in the bath caused an undesirable increase in the coefficient of friction.