稀释剂含量对自蔓延高温合成Si_3N_4-SiC-TiN陶瓷的影响

EFFECT OF DILUENT CONTENT ON Si_3N_4-SiC-TiN CERAMICS PREPARED BY SELF-PROPAGATION HIGH-TEMPERATURE SYNTHESIS

以TiSi2和SiC为原料,利用自蔓延高温合成(self-propagation high-temperature synthesis,SHS)方法合成直径为24mm的Si3N4-SiC-TiN陶瓷。通过理论计算和实验研究了不同孔隙率压坯中稀释剂SiC含量对反应物TiSi2转化率的影响。结果表明:SiC在一定范围内增加有利于TiSi2的氮化, 且含40%(质量分数,下同)SiC和50％SiC的压坯在燃烧合成过程中发生了SiC的氮化反应。压坯孔隙率为50%(体积分数,下同)时,反应物TiSi2 氮化充分,最终产物为Si3N4-SiC-TiN。孔隙率为45%,含量为30％SiC和40％SiC压坯的合成产物中残留游离Si,50％SIC压坯的合成产物中未发现游离Si。在稀释剂含量为35％SiC,氮气压力为150 MPa条件下,所得的Si3N4-SiC-TiN复相陶瓷抗弯强度达430 MPa,断裂韧性为3．6 MPa·m1/2。

Si3N4-SiC-TiN multiphase ceramic samples with a diameter of 24 mm were prepared with TiSi2 and SiC powders as the raw materials by the self-propagation high-temperature synthesis （SHS） method. The effect of different contents of diluent SiC in the samples on conversion percentage of reactant TiSi2 was calculated in theory and an SHS test was carded out. The results show that a certain degree of increase of SiC content was helpful for nitrification of TiSi2, and SiC particles were nitrified during the SHS process in the samples of green compacts with 40% （in mass, the same below） SiC and 50% SiC diluent. The TiSi2 reactants in the green compacts with 50% （in volume, the same below） porosity were fully nitrified and the final products were composed of Si3N4, SiC and TiN. Free silicon was detected in the 30% and 40% SiC-diluted samples with 45% porosity, while no free silicon was found in the 50% porosity green parts. SiaN4~SiC-TiN ceramic with a bending strength of 430MPa and a fracture toughness of 3.6MPa·m1/2 was obtained after the SHS under a nitrogen pressure of 150 MPa and using a green compact with 35 % SiC diluent