Cyclic oxidation kinetics and oxide scale morphologies developed on alloy 617

In this paper, an attempt was done to investigate the cyclic oxidation behaviour of alloy 617, cyclic oxidation tests were carried out in laboratory air at 750, 850, and 950 °C up to 12 cycles (14 h/cycle). The oxidation behaviour of alloy 617 approximately followed the parabolic rate law and the average activation energy is about 206 kJ/mol. At lower temperatures, a two-stage oxidation kinetics were observed and the transition time decreased as the oxidation temperature increased. SEM observations indicated that continuous and relatively irregular oxide layers were formed that had a surface nodular-type structure thickening with temperatures. XRD-patterns and SEM-EDS analysis revealed that the oxide scales were mainly composed of Cr2O3 scale mixed with minor amounts of MnCr2O4. Other oxides were detected such as NiO, TiO2 and MnTiO3. Also, the geometrical-irregularities and Ni-metallic inclusions were detected at the oxide/alloy interface. Moreover, Aluminium was internally oxidized to form A12O3 as elongated particles, which were grown along grain boundaries via branch-like growth. The internal oxidation depth was increased as the temperature increased.