The preparation, microstructure and mechanical properties of a dense MgO–Al2O3–SiO2 based glass-ceramic coating on porous BN/Si2N2O ceramics

Abstract

A dense MgO–Al₂O₃–SiO₂ based glass-ceramic coating was prepared by a doctor blade process on a porous BN/Si₂N₂O ceramic surface followed by heat treatment at 1050 °C under nitrogen flow. The phase composition, microstructure, mechanical properties and water absorption of the coating were studied. The coating consisted of α-cordierite phase with a small amount of glass phase. The dense coating without pores and cracks was favorable to seal and densify the porous ceramic surface due to part of the molten glass infiltrating the surface pores. The coating was defect-free and tightly bonded to the substrate because of a larger bonding area between the coating and the substrate. The elastic modulus and bending strength of the glass-ceramic coating were 37.9 GPa and 67.1 MPa, respectively. Moreover, the coated samples had a high Vickers hardness and low water absorption.