Evaluation of Thermocyclic Oxidation Behavior of HVOF Sprayed (Cr3C2-35% NiCr) + 5% Si Coatings on Boiler Tube Steels

In the present study, the alloying element Si is blended with (Cr3C2-35% NiCr) powder and this composite powder is HVOF sprayed on three different Fe-based steels namely SA213-T22, MDN-310 and SUPERFER 800H. Oxidation studies have been conducted on the coated as well as uncoated specimens at 700 oC in air under cyclic conditions. The weight change method was used to establish the kinetics of oxidation. (Cr3C2-35% NiCr) + 5% Si coated steels showed slow oxidation kinetics and considerably lower weight gains than that of uncoated steels. The superior performance of (Cr3C2-35% NiCr) + 5% Si coatings can be attributed due to the formation of a compact and protective oxide layer consisting of Cr2O3, SiO2, NiCr2O4 and Ni2(SiO4) phases. The uncoated T22 steel suffered a catastrophic degradation in the form of intense spalling of the scale. The combined technique of X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM.EDAX) and X-ray mapping were used to analyze the oxidized products of coated and bare substrate steels.