Effect of rainwater immersion on the wear and friction characteristics of Ni–B and Ni–B–TiO ₂ coatings

Abstract This research aims to study the combined effects of corrosion and wear of the heat treated P20 steel substrate, as well as Ni–B and Ni–B–TiO 2 coatings. To this end, these samples are subjected to long-term immersion tests in rainwater for 75 days before being examined with a pin-on-disk tribometer to explore their tribological behavior. The morphology, structure, and chemical composition are investigated using a Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), and Energy-Dispersive Spectroscopy (EDS) analysis, respectively. After immersion tests, the uncoated P20 HT steel surface exhibits the weakest corrosion and wear resistance. However, Ni–B alloys are promising coatings for protecting against the combined effects of corrosion and wear in natural environments. Compared to Ni–B–TiO 2 , the Ni–B coating exhibits the best corrosion and wear resistance after immersion in rainwater owing to the formation of a dense and thick nickel oxide (NiO) layer. This layer, acting as tribo-film, provides additional protective and lubricating effects, thereby reducing contact between the alumina ball and the coating. The wear rate of Ni–B coating decreased by roughly 40 %.