Effects of electroless nickel interlayer on surface properties of CrN arc-coated austempered ductile iron

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) substrate. The eligibility of applying the EN and CrN duplex coatings on ADI, along with the coating properties, such as surface roughness, surface hardness, and coating adhesion were evaluated and analyzed. Moreover, the microstructures of ADI were observed before and after the surface treatment. In addition, polarization tests were carried out to further understand the effect of the coatings on the corrosion resistance of ADI. The results showed that the unique microstructure of ADI did not deteriorate after EN and CAD treatments. Although the use of EN interlayer resulted in the increase of surface roughness, the interlayer evidently improved adhesion and hardness for the CrN arc-coated substrate. With regards to the corrosion resistance, the coated specimens performed better than that of the uncoated one in 3.5 wt.% NaCl aqueous solution. Moreover, the coating with EN interlayer was superior to that without EN interlayer.