Oxidation Kinetics of Fe-Ni-Cr Alloy at 900 °C

The study of isothermal oxidation of Fe-Ni-Cr alloy was done at 900 °C for 500 hours. The effect of oxidation kinetics and oxide growth behavior on Fe-Ni-Cr alloy were investigated on heat-treated Fe-Ni-Cr alloy to understand the oxidation mechanism on different grain size of alloy. The grain size of Fe-Ni-Cr alloy was varying through heat treatment process at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3 hours soaking time followed by water quench. The heat-treated Fe-Ni-Cr alloy was experienced discontinuous isothermal oxidation test at 900 °C up to 500 hours exposure. The oxidation kinetics plot was calculated based on the weight change per surface area over time. The oxide surface morphology was characterized by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. The heat treatment process recorded an increasing grain size alloy as the heat treatment temperature increase. 8H10 sample indicate the fine grain size, whereas 8H12 sample indicate the coarse grain size. The oxidation kinetics of all samples exhibit the weight gain pattern with fine grain 8H10 sample recorded the lowest weight gain compared to 8H11 and 8H12 samples. All samples were obeyed parabolic rate law indicating the oxide growth rate followed a diffusion-controlled mechanism. The oxide surface morphology of 8H10 sample displayed a continuous oxide scales with formation of grain boundary oxide along the grain boundary area. Similar oxide structure formed on 8H11 and 8H12 samples, except for the formation of crack on the grain boundary oxide on both samples. In addition, 8H12 sample also formed a porous oxide structure.