Effects of group-VB transition metals diborides substitution on HfB2-based ceramics

In order to study the effects of solid solution of group-VB (VB=V, Nb and Ta) transition metal diborides on HfB2 ceramics, the particle size, sinterability, microstructure, and mechanical properties of Nb substituted HfB2-based ceramics were investigated, and compared with the reported (Hf,V)B2 and (Hf,Ta)B2 ceramics. The results showed that the solid solution of group-VB transition metal diborides could refine the particle size of powder and improve the densification by spark plasma sintering. This might be related to the solubility of diboride phase in B2O3 liquid phase. With the addition of SiC, no obvious difference of densification could be observed between (Hf,VB)B2-SiC ceramics. Instead, after the substitution of V, Nb and Ta, the hardness of the (Hf,VB)B2-SiC ceramics was much improved, alongside the decreasing fracture toughness. The influence on mechanical properties of V, Nb and Ta substitution was discussed in combination of the microstructure analysis.