Abstract:Ultrafine-grained and nanocrystalline Ni coatings were prepared without/with using a flexible friction assisted electrodepositing technology from the addtives-free Watts bath. The microstructure, nanoindentation mechanical properties and dry friction and wear behaviour of the both deposits was comparatively studied. The results show that nanocrystalline Ni has much higher nanohardness, elastic modulus, the ratio of nanohardness to elastic modulus than that of ultrafine-grained Ni. The wear mechanism of these both dposits is mainly adhesive wear, but the tribological behavior is different due to the load discrepancy. At low load (1-3 N), nanocryatalline Ni has lower surface roughness and relative smoother worn surface, thus a relative lower coefficient of friction; at high load (5 N), nanocryatalline Ni has a relative coarse worn surface as a result of loose oxidation worn debris, thus a relative higher coefficient of friction. At all the testing load, nanocrystalline Ni has much smaller wear depth and wear volume, and much better wear resistance.