Comparison of Tribological Behavior of Single-Layer and Multilayer Electroless Nickel-Phosphorus Coatings in the Presence of Al2O3 and SiC Reinforcing Particles

Due to their morphology, chemical composition, and phase structure, electroless nickel-phosphorus coatings are used on various substrates, including st37 steel, with the aim of improving working life in various industries. The latest generation of these coatings is the multilayer or hybrid type of nickel-phosphorus electroless coatings. In this research, for the first time, a three-layer Ni-P/Ni-P-Al2O3/Ni-P-SiC coating was produced and its tribological properties were investigated. X-ray diffraction test, energy beam spectrometer, optical and electron microscope images, hardness measurement, roughness measurement, adhesion test (according to ASTM B571 standard), and pin-on-disk wear (according to ASTM-G99 standard) were used for characterization. In the X-ray diffraction pattern related to the multilayer coating, in addition to the amorphous nickel-phosphorus phase, SiC and Al2O3 phases were also seen. The hardness of multilayer coating was 126 Vickers more than that of single-layer coating. The adhesion of all the coatings was very good, so after performing the bending test, no galling was observed in the coatings. In general, it was found that the use of multi-layer coating compared to single-layer coating (with the same thickness) leads to increased hardness, better adhesion, and superior wear behavior. The wear mechanism of the coatings was also evaluated with the help of electron microscope images and energy-dispersive X-ray spectroscopy. The wear mechanism of the electroless nickel-phosphorus coating was delamination and Abrasive, while the hybrid coating changed the mechanism to adhesive by creating a gradient of mechanical properties and lubrication.