Fabrication and characterization of HfB₂-based composites in the presence of TiC and CNT

In this research, the effects of carbon nanotubes (CNTs) on the sinterability, microstructure and hardness of HfB₂-TiC composites were investigated. For this purpose, two HfB₂-TiC specimens, with and without 1 wt% CNTs, were manufactured by spark plasma sintering (SPS) at the temperature of 2000 °C for 8 min holding time under 35 MPa pressure. The microstructure observation and phase analysis were conducted using field emission SEM (FESEM) and X-ray diffraction (XRD) techniques, respectively. It was found that CNTs have no sensitive effects on the densification of HfB₂-TiC composites as well as the growth inhibition of TiC grains. It was disclosed that the initial powders reacted together over the sintering process and led to the synthesis of new phases such as Ti₈C₅, TiC₈, TiB₂ and HfC in the microstructure. According to the XRD analysis, Ti and Hf diffused and dissolved in the HfB₂ and TiC lattices and resulted in the formation of the (Hf,Ti)B₂ and (Ti,Hf)C solid solutions, respectively.