Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2.

ABSTRACT

Transition metal silicides represented by MoSi2have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2at temperatures of 1000 °C-1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2underwent high-temperature selective oxidation reactions at 1000 °C-1200 °C, forming MoO2and SiO2oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2and the phase transformation of SiO2, a continuous Mo5Si3layer with a thickness of approximately 47µm was formed at the SiO2-MoSi2interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3during the high-temperature oxidation of MoSi2coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.