Development of high temperature tribological features of electroless nib and NiB/Al2O3 nanocomposite coatings

This study examines the microstructural, mechanical, and tribological performance of electroless NiB and NiB-Al2O3 coatings applied to mild steel (St-37) substrates. In this dissertation, the electroless NiB and NiB-Al2O3 coatings were deposited onto the steel substrates to produce homogeneous microstructures using the electroless deposition method. The effects of electroless deposition parameters on the microstructure and the friction behaviours of the coatings were investigated in detail. A temperature-controlled wear testing setup was employed to evaluate their high-temperature tribological behavior. The investigation specifically explored the influence of Al2O3 nanoparticle concentration, the configuration of the wear test, and the testing temperature on the dominant wear mechanisms of the coatings. Tribological testing was carried out to assess the performance of the coatings under varying thermal conditions. The tests were conducted at four distinct temperatures: 25 °C (room temperature), 200 °C, 400 °C, and 600 °C to evaluate the influence of elevated temperatures on the friction and wear characteristics of the coatings. A ball-on-disk configuration was utilized for providing controlled and consistent test conditions. During the experiments, a constant applied load of 3 N was applied to simulate realistic contact pressures typically encountered in practical applications. By systematically increasing the temperature, the study aimed to observe and analyze how thermal effects, and changes in material properties, impacted the tribological behavior of the coatings. The results provided valuable insights into the coatings' ability to maintain wear resistance and frictional performance across a wide range of operating temperatures. The experimental findings revealed that the electroless NiB-Al2O3 nanocomposite coatings consistently demonstrated a lower wear rate across all tested temperatures compared to the electroless NiB coatings without Al2O3 reinforcement. This enhanced wear resistance was attributed to the incorporation of Al2O3 nanoparticles, which significantly improved the coatings' ability to withstand wear under varying tribological conditions. Detailed characterization of the microstructures of the coatings, worn surfaces, and wear mechanisms was carried out using advanced analytical techniques, including Scanning Electron Microscopy (SEM) for observing surface morphology, Energy Dispersive X-ray Spectroscopy (EDS) for elemental analysis, X-ray Diffraction (XRD) and Raman Spectroscopy for chemical and structural identification. These techniques provided a comprehensive understanding of the tribological behavior of the coatings and the role of Al2O3 in improving their performance under high-temperature conditions.