Study on Microstructure and Corrosion Resistance of Ni-Co/SiC Nano Composite Alloys for Marine Machinery

Abstract:

In this paper, the effects of SiC nanoparticles on the structure and morphology of Ni-Co coating were investigated by scanning electron microscopy (SEM), energy spectrum analysis (EDS) and X ray diffraction (XRD). The influences of SiC nanoparticles on Ni-Co composite electrodeposition process and the electrochemical corrosion properties of Ni-Co/SiC composite coatings were studied by EIS and Tafel methods. The results show that the addition of Co2+ ions will refine the grain size of the Ni coating, reduce the porosity, transform some structure to amorphous and improve the corrosion resistance. SiC nanoparticles can promote the nucleation and growth of Ni-Co alloy and improve the hardness of the alloys. Compared with Ni-Co alloys, Ni-Co/SiC coatings have excellent corrosion and wear resistance which have the more positive Ecorr, the lower icorr and the larger Rc. Ni-Co/SiC composite coatings have the better stability of service performance, while the corrosion resistance of Ni-Co alloy decreased fast in 3.5 wt.% NaCl solution. The process of corrosion experienced three stages, namely the wetting stage, diffusion control stage which electrolyte transport in the coating and electrochemical control stage in which diffusion process is larger than that of electrochemical’s after electrolytes reach the substrate surface. Ni-Co/SiC alloys can provide long-term protection of marine engineering machinery under the influence of multifactors interaction in seawater environment.

Key words:electrodeposition;SiC;Ni-Co/SiC alloys;corrosion resistance, nano composite coatings