Strengthened interfacial bonding and its effects on fracture mode of TaC ceramics with addition of B

TaC ceramics with 0-0.237 wt% B addition were prepared by hot pressing. The effect of B addition on the phase constitution, interfacial chemistry/bonding and mechanical properties of the TaC ceramics were investigated. Upon B addition, the elimination of O impurity and segregation of B at grain boundaries were evidenced, accompanied by an increase in bonding strength of the TaC grains, to result in a fracture mode change from intergranular to transgranular and a reduced fracture toughness. Addition of excessive B resulted in the formation of TaB 2 and C within TaC ceramics. Further, TaC-TaB 2 -SiC composites were prepared by Si addition. Coherent bonding between TaB 2 and TaC was preserved in the TaC-TaB 2 -SiC composites, and residual stresses due to thermal expansion mismatch of the different phases increased flexural strength and fracture toughness of the composites.