Effect of Surface Morphologies on the Isothermal Oxidation Behavior of MCrAlY Coatings Fabricated by High-velocity Oxyfuel Processes

Abstract

In this study, the effect of surface morphologies on the isothermal oxidation behavior of MCrAlY coatings fabricated by high-velocity oxyfuel (HVOF) processes was investigated. To do so, free standing coatings with as-sprayed and polished surfaces were isothermally oxidized at 1050°C. The thickness of the bond coat was approximately 380μm. The Ra of the as-sprayed and polished surfaces were 6.4μm and 1.1μm, respectively. Before and after oxidation, the surface scale composition and morphology were analyzed by scanning electron microscope (SEM/EDX) and X-ray diffraction. The results show that the roughness of the bond coat significantly affected oxide scales formed on the as-sprayed and polished coatings after 100h oxidation. With increasing roughness (Ra) of the bond coat, the oxidation rate constantly increased and composition of thermal growth oxidation (TGO) changed into oxide mixture consisting of Cr2O3, NiO and spinel. In addition, Scanning Electron Microscope analysis showed that thickness of TGO Layer of the polished CONiCrAlY coating at 1050°C was much thinner than that of the as-sprayed one.