Static and kinetic friction of electroless Ni composite coatings

Abstract

The aim of this study was to examine the static and kinetic friction of electroless Ni coatings of different surface roughening, in unlubricated contact with various counter-body materials. In particular, difference between static and kinetic coefficients of friction was analysed. The Ni coatings deposition was done with electroless plating process. Samples of electroless Ni coatings without and with SiC nanoparticles were heat treated at 300 °С for 6 hours. The microstructure of all samples was characterized by optical microscopy. Microhardness of samples and counter-bodies were also examined. The static and kinetic coefficients of friction was measured for each coating with initial and working surface roughness. Three typical materials used in industry were chosen as a counter-body material. The possibility of stick-slip occurrence was analysed through the static and kinetic coefficients of friction difference. Obtained results show that coatings hardness has strong influence on coefficient of friction, and that slip-stick phenomenon is unlikely to occur, since the differences between static and kinetic coefficients of friction are small. The SiC nanoparticles were added to Ni coating in order to improve the abrasive wear resistance. In the same time, presence of SiC nanoparticles slightly increases the coefficient of friction in unlubricated conditions. Obtained results showed that surface roughness does not have major influence on the coefficient of friction of tested coatings, and that coatings hardness is more influential. The SiC nanoparticles were added to standard electroless Ni coating, and their properties are investigated. Heat treatment was applied to achieve crystalline structure and to improve mechanical and tribological properties. Coefficient of friction testing was performed by simply and easy to operate test rig.