Synthesis and characterization of a novel Zn-Ni and Zn-Ni/Si3N4 composite coating by pulse electrodeposition

To explore better or utterly new performance of Zn-Ni alloy for more challenging applications, a cauliflower-like Zn-Ni and a plate-like Zn-Ni/Si3N4 nanocomposite coating was successfully synthesized by pulse electrodeposition. Their morphology, microstructure, surface and electrochemical properties were studied by various methods. The effects of Si3N4 nanoparticles on microstructure and properties of Zn-Ni matrix were evaluated. The results show that the Zn-Ni alloy with cauliflower-like structure contains about 7-8 wt.% Ni including nanocrystal phase. The plate-like Zn-Ni/Si3N4 nanocomposite coating comprises 4-7 wt.% Ni and 1.5-3 wt.% Si3N4 nanoparticles. Si3N4 nanoparticles were uniformly distributed in Zn-Ni matrix. The inclusion of Si3N4 nanoparticles changed the cauliflower-like Zn-Ni to plate-like Zn-Ni/Si3N4 covered by a nanocrystal layer. The Si3N4 nanoparticles could fill crevices and micron holes, enhancing the effect of physical barrier. The Zn-Ni alloy is rougher than Zn-Ni/Si3N4 composite coating. The coating consists of metallic zinc, nickel and an amount of oxidized/hydroxide zinc species. The Nyquist plot is characterized by two capacitive loops and one low-frequency inductive loop, indicating a zinc dissolution process involving adsorption/desorption of the intermediate. The incorporation of Si3N4 nanoparticles in Zn-Ni coating promotes grain refinement, decreases roughness and improves the performance of the coating.