常压烧结制备Al2O3/SiC纳米复合陶瓷及其显微结构的研究

以微米SiC颗粒和工业氧化铝为原料,采用机械混合法制备Al2O3/SiC复合粉末。将复合粉末煅烧、成型,在1 600℃,2h烧结可制备出Al2O3/SiC纳米复合陶瓷。通过XRD、DSC-TG、SEM和TEM等分析了煅烧和烧结过程中相组成的变化,烧成收缩和微观结构,结果表明:在氧化铝基体中添加80%(质量分数)平均粒径为5μm的SiC粒子,复合粉末经700℃煅烧后再成型,试样于1 600℃烧结,其相对体积质量可达93.8％。SiC粒子主要被包裹在Al2O3晶内形成“晶内型”纳米复合陶瓷。在烧结过程中由SiC氧化形成的SiO2包裹层与基质氧化铝反应形成的无定形莫来石前躯体可大大促进烧结;SiC埋料氧化形成的外壳可有效阻止烧结体内SiC的进一步氧化。

Microstructure and fabrication of Al2O3/SiC nano-ceramics produced by pressureless sintering

Al2O3/SiC nanocomposites were prepared by mechanical mixture of commercial Al2O3 and micrometric SiC powders, followed by pressureless sintering in SiC powder bed at 1 600℃ for 2h. The calcined composite powders were characterized by analysis of X - ray patterns and TEM. Sintering behavior was monitored by dilatometry to optimize the sintering schedule. The results indicated that composite powder containing 8wt% SiC with an average size of 5μm calcined at 700℃ could be sintered to 93. 8% of the theory density. Most of SiC nanoscale particles were randomly located in the Al2O3 grains. Amorphous mullite precursor formed by the reaction between matrix Al2O3 and SiO2 from the SiC oxidation could effectively promote the sintering. Meanwhile mullite coat on SiC particle would prevent the further oxidation of SiC particles. A shell resulted from the oxidation of SiC powder bed could also inhibit the oxidation of the wrapped SiC particles.