Corrosion Behavior of Ti-Si-B-C Nanocomposite Hard Coating with Different Si Contents on 4130 Steel

Abstract

Microstructural, mechanical and electrochemical properties of a Ti-Si-B-C nanocomposite coating with different Si percentages on 4130 steel were investigated. All the films with different SI contents in the range of 10 to 12 mu m thickness showed amorphous structures by X-ray diffraction. The hardness decreased with the increase of Si content in Ti-Si-B-C film. The particle size, pores, roughness and phases were responsible for the decrease of hardness with the increase of Si content. Electrochemical behavior is studied using open-circuit potential, impedance spectroscopy (EIS) and anodic polarization methods in 3.5 wt pct NaCl solution. The corrosion current density (icorr) was much lower, 0.45 to 2.34 mu A/cm(2), with varying Si content compared with uncoated steel (9.37 mu A/cm(2)), and passivation behavior was observed during the polarization study. The EIS fit model suggested the presence of a duplex oxide layer on the Ti-Si-B-C nanocomposite coatings. The Ti-Si-B-C coatings with lower Si (24 pct) content showed the best corrosion resistance compared with higher Si content (36 to 52 pct). Overall, the present study suggests that the hard Ti-Si-B-C nanocomposite coating significantly improved the corrosion resistance of 4130 steel.