将平均粒径分别为150 μm和50 μm的SiC粉体与平均粒径分别为150 μm和50 μm的石墨粉体混合,得到粗粉末床(150 μm SiC+150 μm石墨)与细粉末床(50 μm SiC+50 μm石墨),粉末床中SiC与石墨的体积分数均为50%。采用粉末床技术对圆柱形Si3N4陶瓷预烧体进行放电等离子烧结,研究粗、细粉末床、预烧温度(1 400 ℃和1 500 ℃)和粉末床回收对等离子烧结Si3N4陶瓷圆柱体的变形程度、致密度、物相组成和显微结构的影响。结果表明,采用粗粒径粉末床、1 500 ℃预烧温度和回收使用一次的粉末床制备的Si3N4陶瓷圆柱体,横截面形状保持度最高,达到93%,维氏硬度和断裂韧性分别为(18.73±0.24) GPa和(3.64±0.23) MPa∙m1/2。Si3N4陶瓷的主相为α-Si3N4,晶粒形貌为等轴状。通过引入粉末床可克服放电等离子烧结制备Si3N4陶瓷制品的形状限制,有望实现高性能异形Si3N4陶瓷的制备。
SiC powders with average particle sizes of 150 μm and 50 μm were mixed with graphite powders with average particle sizes of 150 μm and 50 μm respectively to obtain coarse particle size powder bed (150 μm SiC+150 μm graphite) and fine particle size (50 μm SiC+50 μm graphite); the volume fractions of SiC and graphite in the powder bed were both 50%. Pre-sintered cylindrical Si3N4 green body was sintered by spark plasma sintering (SPS) based on powder bed technology. The effects of two different particle size bed powders, pre-sintering temperature (1 400 ℃and 1 500 ℃) and powder bed recovery on the deformation degree, density, phase composition and microstructure of cylindrical Si3N4 ceramics were investigated. The research results show that the circular section retention of cylindrical Si3N4 ceramic prepared by combining the coarse particle size powder bed, a pre-sintering temperature of 1 500 ℃ and a recycled once powder bed is the best, reaching 93%; the Vickers hardness and fracture toughness are (18.73±0.24) GPa and (3.64±0.23) MPa·m1/2, respectively. Due to the low sintering temperature (1 500 ℃), the main phase of the as-sintered ceramics is α-Si3N4; the grain morphology is equiaxed. This study shows that the shape limitation of the Si3N4 ceramics prepared by SPS can be overcame by introducing the powder bed. This technology is expected to realize the preparation of high-performance Si3N4 ceramics with complex shapes.
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