Low-temperature cyclic oxidation behavior of MoSi2/Si3N4 nanocomposite coating formed on Mo substrate at 773 K

The low-temperature cyclic oxidation behavior of MoSi2/(12.9∼17.7) vol.% Si3N4 nanocomposite coating formed on a Mo substrate in air at 500 °C was investigated and compared with that of the monolithic MoSi2 coating using field-emission scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The nanocomposite coating was produced by a prior ammonia nitridation followed by chemical vapor deposition of Si on a Mo substrate. While the accelerated oxidation behavior was observed for the monolithic MoSi2 coating after an incubation period, no pest oxidation but a fairly rapid rate of low-temperature oxidation was observed in the nanocomposite coating with increasing oxidation cycles. The good low-temperature cyclic oxidation resistance of the nanocomposite coating was attributed to the limited formation of massive MoO3 precipitates by reducing the oxygen concentration in oxide scale through the preferential oxidation of Si3N4 particles followed by oxidation of MoSi2 phase. However, fairly rapid oxidation resulted from the crack formation that resulted from the evaporation of nitrogen gas released by oxidation of Si3N4 particles at longer cycles.