CaO-TiO 2烧结助剂对 SiC 基复相材料烧结性能的影响∗

摘要

6 H-SiC and α-Al2 O 3 powders that as raw materials were mixed as mass ratio of 7 ∶3 with CaO and TiO 2 as sintering additives.The green body was preoxidated for 1 h at 1 200 ℃ after being pressed.Sic matrix composites were prepared by pressureless sintering for 1 h in hydrogen atmosphere.The effects of CaO-TiO 2 content and sintering temperature on the sintering properties and phasecomposition were investigated.The re-sults suggested that:withthe increase of sintering temperature form 1 400 to 1 500 ℃,the compactness im-proves significantly.At the sintering temperature of 1 450 ℃,the samples were basically compact.And the sam-ple's apparent porosity decreased to 0.15% with m (CaO-TiO 2 )of 10% added.The reaction of CaO-TiO 2 cristo-balite,with α-Al2 O 3 ,had generated CaAl2 Si2 O 8 at 1 200 ℃,and generated CaTiSiO 5 after 1 300 ℃,which pro-mote the 6 H-SiC further oxidation.In the process of sintering,CaAl2 Si2 O 8 formed liquid glass phase which de-posits mullite and promoted sample’s densification.At 1 500 ℃,the main crystal phase of the composite materi-al was 6 H-SiC,mullite.%以质量分数30％Al2 O 3-70％SiC 为基,外加2％~10％ CaO-TiO 2复合烧结助剂,制备了一系列SiC 基复相材料.研究了不同的烧成温度和 CaO-TiO 2含量对该复相材料烧结性能的影响.研究结果表明,1400~1500℃,随着烧结温度升高,烧结致密性明显提高.烧结温度为 1450℃时,试样基本致密.当烧结助剂达到10％(质量分数)时,显气孔率降至0．15％,陶瓷烧结致密.烧结助剂 CaO-TiO 2,α-Al2 O 3和方石英反应,在1200℃ 已经生成 CaAl2 Si2 O 8,在1300℃以后才开始生成 CaTiSiO 5,促进6 H-SiC 进一步氧化.烧结过程中,CaAl2 Si2 O 8转化为玻璃相,在促进莫来石生成的同时也使试样致密.在 1500℃,复合材料的主晶相为6 H-SiC 和莫来石.