Research Output
Characterization of oxidation kinetics and oxide scale formation on isothermal oxidation of HR-120 ni-based superalloy at 500ºC
Isothermal oxidation behaviour of heat-treated Fe-33Ni-19Cr series ni-based superalloy
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Publication
The HR-120 Ni-based superalloy underwent isothermal oxidation at 500°C in order to better understand the oxidation kinetics and the production of oxide scales. To create small and large grain structure, the HR-120 Ni-based superalloy was heat-treated at two distinct temperatures, 950ºC and 1100ºC. A 500°C for 500 h isothermal oxidation test was performed on the heat-treated alloy of the study examined the oxidation kinetics, oxide phase development and oxide surface morphology of alloy that had undergone isothermal xidation. Plotting weight gain versus surface area allowed for the measurement of oxidation kinetics. The XRD method was used to examine the oxide phase. Surface morphology was investigated with SEM and EDX methods. A parabolic rate law was observed in the oxidation of both heat-treated alloys, suggesting a diffusion-controlled oxide growth mechanism. The alloy’s surface has developed many oxide phases as a result of exposures lasting 500 h. The oxidized samples’ surface morphology after 300 hours shows that overly large Nb-rich oxides are dispersed throughout the continuous oxide scale development. On coarse-grained heat-treated alloys, Nb-rich oxides produced that were abnormally big. This occurrence will initiate a crack that spreads around the oxide.
Publication
The impact of heat treatment on the high temperature oxidation of Ni-based superalloys, specifically the Fe-33Ni-19Cr series, is discussed in this study. This alloy, designated LT950 and HT1160, is heat treated at two distinct temperatures, 950 °C and 1150 °C, for three hours of soaking time, followed by a water quench. Rockwell hardness tests and optical microscopy were used to characterize the heat-treated samples. An isothermal oxidation test was performed on the heat-treated samples for 200 hours at 900 °C. The oxidation kinetics were ascertained by measuring the weight change of the oxidized sample. Oxidized samples were characterized by morphological analysis of the oxide scale using a scanning electron microscope (SEM) and oxide phase analysis using x-ray diffraction (XRD). As a result, the sample's grain size increases with increasing heat treatment temperature. The results of the Rockwell hardness test indicate that the Rockwell hardness number decreases as the heat treatment temperature rises. However, every heat-treated sample that was put through the isothermal oxidation test displayed a pattern of weight gain as the length of exposure increased. Because fine-grained LT950 has a lower parabolic rate constant, it indicates a lower rate of oxidation and therefore has good resistance to oxidation. XRD analysis shows that several oxide layers have formed on the surface of the oxidized sample consisting of Cr-containing oxides from the Cr2O3 and MnCr2O4 phases. SEM analysis of fine-grained LT950 showed uniform oxide scale, while coarse-grained HT1150 showed the formation of cracked and porous structures.