Oxidation protection degradation mechanism and their improvement of RO-R2O-Al2O3-SiO2 enamel coatings for 06Ni9DR alloy steel at 1100–1200 °C

Abstract

RO-R₂O-Al₂O₃-SiO₂ enamel coatings with varying Al₂O₃ and MgO contents were prepared for the oxidation protection of 06Ni9DR alloy steels at 1100–1200 °C. The oxidation protection ratios of these coatings were investigated under different oxidation temperatures and time, and the degradation mechanism as well as the improvements in oxidation protection were explored. The results revealed that the oxidation protection ratio of traditional enamel coating with low crystalline phase content significantly decreased with oxidation test temperatures and time. The viscosity of the liquid phase in coating reduced with temperatures, facilitating oxygen diffusion. Additionally, the interaction between the coating and the oxidation products of alloy steel further reduced the liquid phase viscosity, decreasing coating thickness and shortening oxygen diffusion paths. However, the oxidation protection of coating with higher Al₂O₃ and MgO content were enhanced. These coatings exhibited higher crystalline phases content, which effectively increased the apparent viscosity of enamel coating and prolonged oxygen diffusion paths. The thermal stability of coating with high crystalline phases content also were improved. Among these coatings, the coating with 27.47 wt% Al₂O₃ and 9.93 wt% MgO achieved superior oxidation protection, up to 92.1 %, 76.6 %, and 73.4 % at 1100 °C, 1150 °C, and 1200 °C for 180 min, respectively.