Comparative study of high temperature oxidation behavior and mechanical properties of wire arc sprayed Ni-Cr and Ni-Al coatings

摘要

In the present investigation, Ni-20Cr and Ni-5Al wires were used to deposit coatings on T22 and SA516 boiler steels for protection in high temperature environment. The microstructure, mechanical properties and high temperature oxidation behavior of the deposited coatings were studied. The coatings were found to have a uniform thickness (250-300 mu m) and well intact with the substrate steels. The weight change study was conducted to ascertain the high temperature oxidation behavior of the coatings at 900 degrees C under laboratory conditions. The kinetics of oxidation was established using weight change values for the uncoated and the coated steels. The oxidation products of the coated and uncoated samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray mapping analysis. The results showed that Ni-20Cr coating on SA516 steel reduced the weight gain by 99%, whereas the Ni-5Al coating on T22 steel decreased weight gain by 83% than the bare steel. This higher oxidation resistance is due to the presence of a protective phases in the oxide scale (Cr2O3, NiCr2O4, NiO, and Al2O3), lower porosity (2%), and higher micro hardness of the coating.