High Temperature Properties and Microstructure of Boron Nitride-Zirconia/Corundum/Mullite Composites

摘要

The high temperature properties and microstructure of boron nitride matrix with addition of 10wi%～30wt% zirconia/corundum/ mullite hot-pressing sintered have been studied. The results reveal that addition of zirconia/ corundum/mullite to BN-based material results in enhancement of bending strength and fracture toughness that may be due to the dispersion strengthening and toughness effects caused by the dispersion of oxide particles in the interwoven structure of BN. Furthermore, when oxide addition does not exceed 20wt% , the composite still retains excellent thermal shock resistance characteristic of BN material. The 9Al_2O_3 · 2B_2O_3 formed during the sintering process create a pull-out effect when the material tends to fracture, which may be beneficial for improvement of mechanial properties. The oxidation kinetics model has been worked out, together with formula for activation energy and rate. Thermal fatigue life formula has been derived, and the activation energy for subcritical crack growth and the stress intensity exponent have been calculated.