Abstract
The effect of Ultrasonic Nanocrystal Surface Modification (UNSM) on the structural, mechanical, and tribological properties of WC–12Co coatings deposited by high-velocity oxygen fuel (HVOF) spraying onto 12 × 18H10T steel was investigated. The coatings were treated with UNSM using four combinations of amplitude (20 and 50 μm) and static load (10 and 40 N). Morphology and microstructure were evaluated using scanning electron microscopy; additionally, surface roughness, porosity, Vickers microhardness, Martens hardness, coefficient of friction, and acoustic response during scratching under a constant load were determined. The greatest relative reduction in Ra was observed for L2 (64.97%), while L4 exhibited the lowest final Ra value (1.512 ± 0.256 μm) and the greatest reduction in Rz (76.07%) and porosity (from 29.632% to 4.838%). The reduction in Ra and Rz was statistically significant for all treatment conditions. The maximum Martens hardness was observed for L3 (9162 N/mm2), whereas the differences in Vickers microhardness relative to the untreated coating were not statistically significant. The average coefficient of friction after UNSM did not decrease relative to the untreated coating, whereas samples L2–L4 exhibited lower maximum acoustic emission values during scratching. Overall, the results indicate a non-monotonic dependence of the coating properties on UNSM amplitude and static load. The findings indicate that the selection of the UNSM treatment mode should be based on the required balance between surface morphology, mechanical properties, and resistance to localized mechanical damage.