High Temperature Isothermal Oxidation of Heat-treated HR-120 Ni-based Alloys

The effect of heat treatment of HR-120 Ni-based alloys on the isothermal oxidation at high temperature was studies. HR-120 Ni-based alloys was undergo a heat treatment process at two different temperatures, namely 1000 °C and 1200 °C for 3 h soaking time, followed by water quench. The heat-treated samples were then undergoing an isothermal oxidation test at 500 °C for 500 h exposure time in air. Oxidized samples have been characterized in terms of the kinetics of oxidation, phase analysis using x-ray diffraction (XRD) and oxide surface morphology using scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM) equipped with energy dispersive x-ray (EDX) spectrometer. The heat treatment process exhibits an increasing of average grain size alloy as the temperature increases. Whereas, the oxidation kinetics of oxidized samples exhibits a parabolic rate law, representing a diffusion-controlled oxide growth rate. The oxidized of heat-treated sample at 1000 °C recorded low oxidation rate with low parabolic rate constant values. The oxide surface morphology of oxidized samples indicates the formation of continuous oxide scales with overgrown Nb-rich oxide particles after exposure for 300 h. At 500 h exposure time, the formation of Nb-rich oxide particles was growing with evidence of crack occurred around the overgrown oxide particles.