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.

Isothermal Oxidation Behaviour of 800H Nickel-Based Alloy

“…The refined grain structure has evidently show good oxidation protection on the alloy. The fine grain structure recorded a lower oxidation rate that enhance the oxidation protection on the alloy system [7][8]. On the other hand, establishment of stable oxide layer also reported, which is developed by fine grain structure.…”

“…Fine grain FG sample provide higher area of grain boundary that intensify a diffusion path of outward metal ion diffusion toward the alloy-gas interface. The higher diffusion rate at the beginning of the oxidation process will intensify the rapid establishment of initial oxide layer which perfectly encapsulate the whole alloy surface induce by the lateral diffusion [7][8]. As fully oxide layer covered the alloy surface, the oxide growth was dominated by vertical growth to further increase the oxide dimension to enhance the optimum thickness of the oxide scale to provide maximum protection.…”

“…When sufficient oxide thickness achieved, the oxidation rate starts to reduces due to the establishment of optimal oxide scale. The study on the oxidation rate can be seen through different experiment approach such as assorted alloy structure, surface modification and also a thermal treatment [5][6][7][8]. The refine grain structure has been notable to established excellent oxidation protection by lowering the oxidation rate and formation of uniform and adherence oxide layer [7][8].…”