Investigation of Isothermal Oxidation on Heat- treated Fe-40Ni-24Cr Alloy at 950°C

Abstract

In this research, Ni-based superalloy which is Fe-40Ni-24Cr alloy was experienced a heat treatment process to alter the grain size of the sample to observe its influence on the oxidation properties. The alloys were heat-treated at temperatures of 950°C, 1050°C, and 1150°C for 2 hours followed by water quench. The heat-treated alloys were undergoing an isothermal oxidation test at 950°C for 150 hours in laboratory air. The weight gain of oxidized heat-treated alloy was recorded in order to determine the oxidation kinetic of the test samples. Scanning electron microscopy (SEM) technique was employed in this study to analyze the oxidation behaviour of heat-treated samples. Grain size measurement shows that the grain size increases as the heat treatment temperature increases. The oxidation rate of heat-treated Fe-40Ni-24Cr alloy obeys the parabolic rate law indicating the diffusion-controlled oxide growth mechanism. The fine grain size of alloy heat-treated at 950°C possess a better oxidation resistance and has a lower oxidation rate compared to coarse grain samples. The surface morphology indicate that the fine grain heat-treated alloy at 950°C shows uniform oxide layer formed on the surface, while alloy heat-treated at 1050°C and 1150°C shows the uneven oxide growth, oxide flaking and oxide spallation.