超重力场燃烧合成TiC-TiB_2凝固陶瓷组织与性能

Microstructure and properties of solidified TiC-TiB_2 composites prepared by combustion synthesis in high-gravity field

通过调整反应体系中Ti、C及B之间的原子摩尔比,采用超重力下燃烧合成工艺,制备出TiB2系列摩尔分数的TiC-TiB2复合陶瓷。利用场发射扫描电镜(FESEM)观察了复合陶瓷微观组织,研究了TiB2成分对复合陶瓷力学性能的影响。结果表明:随着TiB2摩尔含量增加,陶瓷基体逐渐从TiC球晶组织转化为TiB2片晶组织,在TiB2摩尔分数为50%时,可获得细晶乃至超细晶TiC-TiB2复合陶瓷,而且残留于基体上的α-Al2O3夹杂量也最低。陶瓷相对密度、Vickers硬度与弯曲强度均在50%TiB2(摩尔分数,下同)时呈现最大值,而陶瓷断裂韧性则在66.7%TiB2时出现最高值。陶瓷断裂模式为TiC穿晶断裂与TiB2沿晶断裂的混合模式,且随TiB2摩尔分数增加至66.7%,TiC穿晶断裂倾向显著减弱而TiB2沿晶断裂倾向明显增强。TiC-TiB2细晶及超细晶凝固组织的获得使TiC-50%TiB2复合陶瓷在小尺寸TiB2片晶诱发的裂纹偏转、裂纹桥接及片晶拔出增韧机制作用下,具有最高的弯曲强度及较高的断裂韧性。

By changing the mole ratio of Ti, C and B in primary reaction system, TiC-TiB2 composite ceramic with different TiB2 mole content were prepared by combustion synthesis in high-gravity field. The microstructure of composites was characterized by FESEM. The influence of the TiB2 composition on the mechanical properties of composite ceramic was studied. The results indicate that the matrix of TiC-TiB2 composite ceramics transforms from TiC grains to TiB2 platelets with increasing TiB2 mole content, moreover, the fine-grained microstructures and even ultrafine-grained microstructures are achieved in TiC-50 %TiB2, while volume fraction of α-Al2O3 inclusions in the ceramic also reaches the lowest value. The relative density, Vickers hardness and flexural strength of ceramics simultaneously reach the maximum values as the mole content of TiB2 is 50% in the ceramic, whereas the maximum fracture toughness is achieved in TiC-66.7%TiB2. FESEM fracture morphologies of the ceramics show that intercrystalline fracture is enhanced while transgranular fracture is weakened inversely with increasing mole content of TiB2 to 66.7%. FESEM crack propagation paths of TiC-TiB2 composite ceramics show that the highest flexural strength is achieved in TiC-50%TiB2 composite ceramic due to both the achievement of solidified fine-grained and ultrafine-grained microstructures and the presence of intensive toughening mechanisms of crack deflection, frictionally crack-bridging and pull-out by a large number of fine TiB2 platelets.