| Abstract: | Nano SiC-BN composite powders were prepared by dissolving analytically pure H3BO3 and CO(NH2)2 with the mole ratio of 1 :2.5 in the absolute alcohol,adding 80% β-SiC with 0.2 μm average grain size while stirring,firing at 850 ℃ in nitrogen(purity:99.99%,pressure:0.92-0.93 MPa)for 15 h.1Vano SiC-BN composite specimens were prepared by hot-pressed sintering the nano SiC-BN composite powder in N2 atmosphere with 0.92-0.93 MPa and at 30 MPa axial pressure for 0.5-1 h at 1 750-1 800 ℃.The thermal shock resistance of nano SiC-BN composites was studied by three-point bending,TEM and SEM.The results show that,adding BN can decrease the modulus of elasticity of SiC materials,which improves thermal shock resistance;furthermore,because of the large difference of thermal expansion coefficient between matrix SiC and second phase hexa-BN,thermal mismatch effect results in intercrystalline delamination of h-BN grains and forming many micropores in composite ceramic,which can relax the thermal expansion caused by high temperature effectively,and improve the thermal shock resistance significantly. |
