Anti-oxidation modification behaviors and mechanisms of ZrB2 phase on Si-based ceramic coatings in aerobic environment with wider temperature region

Abstract

To improve the modification effect of ZrB2 phase on Si-based ceramic coatings in aerobic environment with wider range of temperature, ZrB2 was utilized to modify the SiC coating by the technique of liquid phase sintering. The modification behaviors of ZrB2 phase on oxidation inhibition ability of SiC coating were investigated in wider range of temperature through the TG oxidation tests (room temperature-1773 K). When the synthetic temperature is 1700 °C, pure phase ZrB2 powders were synthesized through the way of carbothermal reduction, the average particle size of which is 531 nm. The SiC coating modified by ZrB2 is comprised of ZrB2 and SiC phases, the thickness of which is about 200 μm. With the modification of ZrB2 phase, the oxidation resistance of the SiC coating is significantly enhanced, especial the temperature region below 1200 °C, leading to the delay of initial mass loss temperature (about 260 °C) and slowing down mass loss rate (reduced by about 67%) in the fastest mass loss area. While the final mass loss of the coated graphite substrate decreased from 18% to 5%. Owing to the formation of the protective B2O3, the fast weight gain temperature region (from 700 °C to 1240 °C) in the TG curve of the ZrB2 powders effectively compensate the weakness of the SiC coating in this temperature region. With the movement of the increasing SiO2 glass layer to cover the surface of the coating, Zr-oxides consisted of ZrO2 and ZrSiO4 were gradually peeled into tiny oxide particles to form Zr-oxides-rings. The refractory Zr-oxides-rings and the unpeeled large Zr-oxides-obstacles construct skeleton inlayed in the SiO2 glass layer, demonstrating the ability of restricting the growth of microcrack, which is responsible for the remarkably enhanced anti-oxidation modification effect of ZrB2 phase.