粉末粒径对热压烧结碳化硼致密化及力学性能的影响

采用平均粒径分别为3.5 μm、1.5 μm和200 nm的碳化硼粉体为原料经1850℃热压烧结制备了碳化硼陶瓷, 研究了粉体粒径对陶瓷烧结致密化过程及其性能的影响。根据保温时间对线收缩率的影响及热压初期的塑性流动机理, 得出了不同粉体间烧结初期的激活能差。结果表明: 在相同工艺条件下, 随着粉体平均粒径的减小, 粉体的扩散激活能降低, 致密化初始温度降低, 而且完成塑性流动所需时间也会明显缩短, 致密化速率加快, 致密度增大; 碳化硼陶瓷的显微结构与力学性能亦随着粉体粒径的减小而改善; 1850℃保温1 h后, 平均粒径为200 nm的粉体制备的碳化硼陶瓷相对密度可达90.5%, 硬度为(17±1.8) GPa。

Effect of Particle Size on Densification and Mechanical Properties of Hot-pressed Boron Carbide

Monolithic B₄C ceramics were prepared by hot-pressing using three types of B4C powders with average particle of 3.5 μm, 1.5 μm and 200 nm, respectively. The effect of particle size on densification and microstructure of sintered ceramics was studied. The activation energy difference of the starting powders in the initial sintering stage was obtained in terms of dwelling time as a function of linear shrinkage and plastic deformation mechanism. The result shows that at the same process, the diffusion activation energy and densification initial temperature of the powders decrease with the mean particle size decreasing, and the time of plastic flow in the initial sintering stage is also shortened markedly, while the relative density and densification rate are higher. The microstructure and mechanical properties of sinterd samples are also improved with mean particle size decreasing. The relative density of 90.5% and hardness of (17±1.8) GPa are achieved for the B4C ceramics sintered from the powders with mean particle size of 200 nm for 1 h at 1850℃.