关键词: TiB₂, Si₃N₄-SiC, 致密化, 气固生长机制

Abstract: To improve the performance,reaction sintered Si₃N₄-SiC refractories were prepared by reaction sintering at 1 400 ℃ for 2 h using SiC (particles and fines) and Si powder as the raw materials,TiB₂ fine powder as the additive.The effects of the TiB₂ fine powder addition (0,0.2%,0.4%,0.6%,and 0.8%,by mass) on the bulk density,modulus of rupture,phase composition,and microstructure of the reaction sintered Si₃N₄-SiC refractories were studied using MIP,XRD,and SEM,and the densification mechanism was analyzed.The results show that:(1)adding an appropriate amount of TiB₂ helps to improve the bulk density and hot modulus of rupture at 1 200 ℃,increasing the proportion of small pores (≤1 μm);(2)with the increasing TiB₂ addition,the content of Si₂N₂O impurity phase decreases,the nitridation rate of silicon powder improves;Si₃N₄ exists as a whisker structure at the beginning,then evolves into well-developed long rods,and finally grows abnormally;(3)the densification mechanism is as follows:a small amount of TiB₂ can increase the partial pressure of SiO gasous phase and promote the growth of Si₃N₄ whiskers,which follow the gas-solid growth mechanism;when increasing the TiB₂ addition to 0.6%,Si₃N₄ develops into long-rod shapes under moderate high-temperature liquid phase,forming a three-dimensional network structure;when continuing to increase the TiB₂ addition to 0.8%,the liquid phase in the samples increases again,and the rod-shaped Si₃N₄ grows abnormally;(4)when the TiB₂ addition is 0.6%,the comprehensive performance of samples is the best,with the bulk density of 2.75 g·cm^-3,apparent porosity of 11.6%,cold modulus of rupture of 40.2 MPa,and hot modulus of rupture at 1 200 ℃ of 47.4 MPa.

Key words: TiB₂, Si₃N₄-SiC, densification, gas-solid growth mechanism