Oxide Growth Behaviour of 800H and HR-120 Series Ni-based Alloys on Isothermal Oxidation

The isothermal oxidation of two types of Ni-based alloy, alloys 800H and HR-120 was investigated in this study. The alloy underwent an isothermal oxidation test at 950 ºC for 150 hours of exposure. Oxdised alloys were tested using oxidation kinetics methods, phase analysis using X-ray diffraction (XRD) and oxide morphology using scanning electron microscopy (SEM) techniques. Oxidation kinetics were determined based on the weight change per surface area of the oxidised alloy over a 30-hour interval. As a result, both alloys displayed a pattern of weight gain as the exposure period increased. Both alloys have followed a parabolic rate law, indicating a controlled kinetics of oxide scale diffusion. XRD analysis showed that the main Cr-containing oxide has formed on the surface of the alloy with the addition of Ti oxide for the 800H alloy and Nb oxide for the HR-120 alloy due to the different alloying element content of the two alloys. Oxide surface morphology records the uniform oxide scale that forms on the surface of the alloy.