Friction and contact resistance of nanocomposite Ti–Ni–C coatings

Ceramic nanocomposite coatings in the Ti–Ni–C were deposited using PVD and studied with respect to tribological properties and contact resistance. It was shown that coatings could be deposited combining of a low contact resistance and a low friction coefficient against silver, making them suitable for use in high performance electrical contacts.Nine coatings with different amounts of C and Ni were deposited. Coatings on flat Ni plated copper substrates were tested in a tribological ball-on-disc setup against ball bearing steel balls. Depending on primarily the amount of carbon the coatings showed very different friction coefficient and wear rate. The coatings were also deposited on cylindrical Ni plated copper substrates. Using geometrically identical silver plated cylinders as counter surface these were evaluated in a test setup better resembling a real life electrical contact. For most coatings a low electrical contact resistance was measured. The evolution of friction coefficient and contact resistance was correlated to wear marks and contact tracks, with their generated tribofilms, as examined after testing using electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.

Research highlights
► Long term stability and friction as low as 0.15, could be obtained against ball bearing steel during 70,000 revolutions.
► Generally, the coatings with high carbon content showed the best tribological behaviour.
► All nanocomposites showed low dynamic contact resistance.
► The dynamic contact resistance followed the coating resistivity.
► Differences between static and dynamic contact resistance are due to oxides on the coating surfaces that brake during sliding.