Effects of CrN/EN and Cr 2O 3/EN duplex coatings on corrosion resistance of ADI

Abstract

This study utilized electroless nickel (EN) and cathodic arc deposition (CAD) technologies, with the known advantage of low processing temperature, to treat the austempered ductile iron (ADI) substrates. The eligibility of applying the CrN/EN and Cr 2O 3/EN duplex coatings on ADI, along with the effect of these coatings on corrosion resistance of ADI were evaluated. Two kinds of corrosion media were used in this experiment such as NaCl and H 2SO 4 aqueous solutions. In addition, surface roughness and film adhesion of the coatings were analyzed, and the microstructures of ADI were also observed before and after the surface treatments. The results showed that not only these coatings have been smoothly deposited on the substrate, but also ADI's unique microstructure did not deteriorate after the surface treatments. Although the use of EN interlayer resulted in the slight increase of surface roughness, this EN interlayer evidently improved the adhesion of the CrN and Cr 2O 3 coated substrates. In the corrosion resistance, all the coated ADIs performed better than that of uncoated one when the specimens were exposed to 3.5 wt.% NaCl and 10 vol.% H 2SO 4 aqueous solutions, respectively. In particular, the Cr 2O 3/EN coated specimen had the best performance on corrosion protection for ADI among all the coated specimens.