Preparation and Corrosion Resistance Study of Nano-La2O3 Reinforced Electroless Ni-B Coatings

This study was conducted to explore how varying the concentration of nano-La2O3 particles in the plating bath influences the morphology, constitution, and corrosion resistance of Ni-B composite coatings deposited on N80 carbon steel via electroless plating. The novelty of this work lies in the systematic investigation on the co-deposition behavior and grain refinement mechanism of nano-La2O3 in electroless Ni-B system, which has been rarely reported in previous studies. The microstructure and chemical composition of the coatings were characterized through a combination of SEM, EDS, XPS and XRD analyses. SEM confirmed that a dense Ni-B/La2O3 composite coating was formed, with a uniform thickness of approximately 10 μm, and the nano-La2O3 particles were evenly distributed. XPS analysis verified the presence of B, C, O, Ni and La, while XRD analysis revealed a refinement in crystalline size due to the addition of the nanoparticles. The corrosion resistance enhancement mechanism is attributed to the triple synergistic effect: nano-La2O3 pins grain boundaries and refines Ni-B grains to the minimum average size of 12.943 nm at the optimal concentration of 8 g·L−1; the refined grain structure promotes the formation of a continuous and dense Ni(OH)2 passive film; the uniformly dispersed nanoparticles act as physical barriers to block the penetration of corrosive media. Electrochemical measurements demonstrated that this coating exhibited outstanding anti-corrosion performance, as confirmed by a remarkably positive corrosion potential (Ecorr = −0.37189 V) and a minimal corrosion current density (Icorr = 3.7524 μA/cm2). The results conclusively show that nano-La2O3 reinforcement effectively enhances the corrosion protection performance of electroless Ni-B alloy coatings.