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

摘要： 以SiC颗粒和细粉、Si粉为原料,TiB₂细粉为添加剂,采用反应烧结法经1 400 ℃保温2 h制备了Si₃N₄-SiC耐火材料,以期改善它的性能。通过MIP、XRD、SEM等研究了TiB₂细粉添加量(加入质量分数分别为0、0.2%、0.4%、0.6%和0.8%)对反应烧结Si₃N₄-SiC耐火材料致密性、抗折强度、物相组成和显微结构的影响,并分析了致密化机制。结果表明:1)添加适量TiB₂有助于提高试样体积密度和高温抗折强度(1 200 ℃),增加≤1 μm小孔比例;2)随着TiB₂添加量的增加,Si₂N₂O杂相含量减小,Si粉氮化率提高,Si₃N₄开始为晶须状,后演变为发育良好的长棒状,最后异常长大;3)致密化机制为:添加少量TiB₂可增加SiO气相分压,促进Si₃N₄晶须遵循气固机制生长;当TiB₂添加量为0.6%(w)时,Si₃N₄在适量高温液相作用下发育为长棒状,形成三维交叉网络结构,继续增加TiB₂添加量至0.8%(w),试样中液相再次增多,棒状Si₃N₄异常长大;4)当TiB₂添加量为0.6%(w)时,试样综合性能最佳,其体积密度为2.75 g·cm^-3,显气孔率为11.6 %,常温抗折强度为40.2 MPa,1 200 ℃高温抗折强度为47.4 MPa。

关键词: TiB₂, Si₃N₄-SiC, 致密化, 气固生长机制