Influence of Ti on Oxide Formation During Isothermal Oxidation of 800H Ni-Based Alloys

In this research, a 800H Ni-based alloy was experienced a solution treatment procedure at two different temperatures. The solution-treated alloys were undergo a high-temperature oxidation under isothermal conditions at 500°C for 500 hours in laboratory air. The alloy was characterized using OES, XRD, SEM and FESEM equipped with an EDX spectrometer. It was found that the solution-treated alloy at 950°C produced a small grain size, and alloy treated at 1100°C produced a large grain size. The XRD results show that various oxides phases were detected. The oxidation kinetics followed the parabolic rate law indicating the oxide was formed based on diffusion-controlled oxide growth rate. The alloys with small grain sizes exhibited a lower oxidation rate, hence have excellent oxidation resistance. This is due to the accessibility of the high ion diffusion route through the grain boundaries of small-grained alloy and thus permits the speedy establishment of the initial oxide layer. Uniform oxide scale formed on a small-grained oxidized sample with visible overgrow discrete oxide particle comprised of Ti-rich oxide. The large-grained oxidized sample indicates evidence of oxide exfoliation indicating poor oxidation protection.