Oxide Growth Behaviour of Fe-Ni-Cr Alloy at High Temperature Oxidation

Abstract

The isothermal oxidation test has been investigated on two types of Fe-Ni-Cr alloy, namely Fe-33Ni-19Cr and Fe-40Ni-24Cr alloys. Both alloys were undergoing an isothermal oxidation test at temperature of 500? for 500 hours exposure time. The weight change per surface area of the oxidized samples has been recorded to calculate the oxidation kinetics of both alloys. The oxide growth behaviour of oxidized samples has been examined using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. The oxide phase formed on the sample surface has been analyzed using x-ray diffraction (XRD) technique. The results show that both alloys were followed a parabolic rate law, indicating a diffusion-controlled oxide growth mechanism. In addition, the oxidation kinetics indicating an increasing weight gain trend as the exposure time increase. Several oxide phases had formed on the oxidized surface of both alloys, consists of Cr-rich, Ti-rich, Fe-rich and spinel oxide structure. The surface morphology of both alloys demonstrated a continuous oxide scale formed on the alloy surface. Additionally, Fe-33Ni-19Cr alloy recorded a formation of Ti-rich oxide, whereas, Fe-40Ni-24Cr alloy displayed a formation of overgrown Nb-rich oxide particle which. Roles of the precipitates in oxidation mechanism give new insights into the alloy optimization.