关键词: B₄C, Si₃N₄/Si₂N₂O结合SiC, 抗热震性, 干熄炉, 斜道区

Abstract: Si₂N₂O was synthesized using Si powder and SiO₂ micropowder as raw materials and treating at 700 ℃ in the air atmosphere and then at 1 400 ℃ in the nitrogen atmosphere.The effect of the B₄C addition (0,1.0%,2.0%,3.0% and 4.0%,extra adding,by mass) on the synthesis of Si₂N₂O was studied.With the optimal B₄C addition,Si₃N₄/Si₂N₂O bonded SiC samples were prepared after firing at 700 ℃ for 5 h in the air atmosphere and then at 1 400 ℃ for 5 h in the nitrogen atmosphere.The thermal shock resistance of the samples was evaluated by the retention ratio of the modulus of rupture after 5 cycles of thermal shock(1 300 ℃,air quenching).The phase composition and the microstructure of the samples before and after thermal shock were analyzed.The results show that:(1)the optimal B₄C addition is 3%;B₄C preferentially reacts with O₂ to generate B₂O₃ at 700 ℃ in the air atmosphere,which provides sufficient liquid phase for the formation of plate-like Si₂N₂O at 1 400 ℃ in the nitrogen atmosphere;(2)after thermal shock,the sample added with B₄C has complete Si₂N₂O bonding phase and increased strength retention ratio from 67.5% to 88.5% compared with the sample without B₄C;at the same time,B₂O₃ transforms to BN of good thermal conductivity and self-lubricating property through the carbothermal reduction nitridation reaction,which improves the thermal shock resistance and continues to protect Si₃N₄/Si₂N₂O bonded SiC materials during service.

Key words: boron carbide, Si₃N₄/Si₂N₂O bonded silicon carbide, thermal shock resistance, coke dry quenching furnace, inclined channel area