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

摘要

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°C 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.