可加工Si_3N_4/BN复相陶瓷的制备及性能研究

Investigation of Fabrication and Properties of Machinable Si_3N_4/BN Composite Ceramics

采用化学溶液法混料,然后用氢还原氮化法制备出具有包覆结构的Si3N4/BN纳米复合粉体,复合粉热压后获得较高强度,同时又具有良好加工性能的复相陶瓷。扫描电镜(SEM),X射线衍射(XRD)分析表明:复相陶瓷中氮化硼以六方晶(h-BN)均匀分布于以α-Si3N4为基体相的晶界与晶内,并抑制α-Si3N4的晶粒长大使基体晶粒细化。良好加工性能的获得是由于h-BN易沿其层间解理以及h-BN与α-Si3N4两相由于热膨胀失配产生的弱界面易在剪切方向剥层所致。

The Si3N4/BN nano-composite powders have been prepared by reducing the mixture of alpha-Si3N4 powder, H3BO3, and CO(NH2)(2) in hydrogen, then the machinable Si3N4/BN composite ceramics of good mechanical properties are fabricated by a hot-pressing sinter. According to the SEM micrographs and XRD analysis of the composites it is shown that the boron nitride in form of h-BN phase is evenly dispersed in the intragranular and intergranular fields of silicon nitride in form of alpha-Si3N4 phase and the alpha-Si3N4 grain growth is inhibited by the h-BN phase. The composites have a better machinability because the h-BN is easily cleaved along its weak cell boundaries and the weak interfaces due to their thermal expansion - mismatch between h-BN phases and alpha-Si3N4 phases are readily delaminated in shear.