Optimized electrophoretic zinc oxide coating on SS316L with enhanced hardness and scratch resistance

Abstract

The major issues in electrophoretic deposition of ZnO coating on SS316L are lack of adhesive strength, control of electrophoretic mobility, and the presence of cracks in the coating. The novelty of the present study is mainly focused on optimizing the electrophoretic deposition parameters by varying the concentration of the ZnO NPs (1.0 g/L and 1.5 g/L) and the applied voltages (30 V and 40 V) to minimize these coating defects. The impact of nanoparticle concentrations and applied voltages on the morphology, roughness, phase composition, functional groups, hardness, surface energy, and scratch resistance of ZnO coatings was analyzed. Various deposition conditions produced different crystal sizes ranging from 16 to 24 nm. Among the deposition conditions, the ZnO-3 coating demonstrated an increased crystal size with decreased microstrain. However, a higher applied voltage of 40 V in the ZnO-3 coating significantly increased the electrophoretic mobility of the NPs, leading to the agglomeration of the NPs and the formation of larger crystals. Furthermore, morphological analysis confirmed uniform distribution and higher deposition rates in the ZnO-2 coating. The ZnO-2 coating deposited at a concentration of ZnO NPs (1.5 g/L) and a lower applied voltage (30 V), exhibited higher coating hardness (216 HV), lower surface roughness (0.207 µm), low surface energy, and better adhesive strength than the other three ZnO coatings. Thus, the optimized electrophoretic coating of ZnO-2 on SS316L emerged as a solution to reduce the cracks, improve the adhesion with better control over electrophoretic mobility.