Improved thermal shock and oxidation resistance of β-SiAlON incorporated with h-BN

Abstract

β-SiAlON ceramics incorporated with h-BN were prepared by gel casting combined with reaction bonding procedure. With the h-BN addition varying from 0 to 20 wt%, the bending strength was degraded from 102.5 MPa to 60.0 MPa. Compared to monolithic β-SiAlON, β-SiAlON/h-BNs have significantly better thermal shock resistance. At high temperature in air atmosphere, mass gain curves of both β-SiAlON and β-SiAlON/h-BN exhibited platform stage after certain oxidation time. Higher temperature benefits formation of protective layer which inhibited oxygen diffusion, then the oxidation of the samples was stagnated. Addition of h-BN make it easier to form the protective layer. Furthermore, B2O3 from oxidation of h-BN could inhibit the crystalizing of the glassy phase, hence, more stable protective layer could form stagnating oxidation process. Addition of h-BN in β-SiAlON exhibited excellent enhancement on thermal shock resistance and oxidation resistance, which is of vital importance for application in high temperature environments. An empirical biexponential model was suggested for describing the oxidation behavior of the ceramic material containing open pores prepared in this work.