Isothermal and cyclic oxidation behavior of in-situ grown MoSi2-SiC coating on Mo substrate at 1300 °C

Abstract

We prepared the in-situ grown composite coating layer on Mo substrate to improve the resistance of MoSi2 coating against cyclic oxidation by introducing SiC reinforcement to reduce the thermal expansion mismatch with Mo substrate. Composite coating of MoSi2-19.3 vol% SiC was fabricated using a two-step approach of Mo2C coating on Mo substrate followed by siliconizing to achieve uniform dispersion of nanosized SiC particles in a matrix of equiaxed MoSi2 grains. The superior performance of this coating over monolithic MoSi2 coating was clearly demonstrated through evaluations of bot its isothermal and cyclic oxidation behavior at 1300 degrees C. In both coatings, diffusion-limited growth of oxide film was observed as indicated by parabolic weight gain up to 100 h at 1300 degrees C. Slightly faster oxidation rate in this isothermal test was observed in the composite coating and mainly attributed to the fast oxygen transport through open pores and blowholes created by CO gas evolution from the internal oxidation of SiC particles. Composite coating gave rise to drastic improvement of cyclic oxidation resistance at 1300 degrees C while monolithic MoSi2 coating broke into pieces in less than 35 cycles. Both equiaxed grains of MoSi2 and SiC dispersion was effective in suppressing the occurrence of through-thickness cracks in coating layer due to lower thermal stress generated during cooling to room temperature.