Corrosion behavior of duplex coatings

The titanium alloys are used in defense, aerospace, automobile, chemical plants and biomedical applications due to their very high strength and lightweight properties. However, corrosion is a life-limiting factor when Ti alloys are exposed to different chemical environments at high temperatures. In the present paper, duplex NiCrAlY/WC–Co coating is coated onto Ti6Al4V substrate to investigate the corrosion behavior of both coated samples and the substrate. The duplex coating was performed with NiCrAlY as the intermediate coat of 200μm thickness deposited by HVOF process and WC–Co ceramic top coat with varying thicknesses of 250μm, 350μm and 450μm deposited by DS process. Potentiodynamic polarization tests were employed to investigate the corrosion performance of duplex coated samples and substrate in Ringer’s solution at 37°C and pH value was set to 5.7. Finally the results reveal that 350μm thick coated samples showed highest corrosion resistance compared to 250μm thick samples as well as bare substrate. However, the 450μm thick coated sample showed poor corrosion resistance compared to the substrate. The scale formed on the samples upon corrosion was characterized by using SEM analysis to understand the degree of corrosion behavior.