Synthesis and characterization of vanadium boride powders and their sintered bodies

In the present study, mechanochemical synthesis, pressureless sintering (PS) or spark plasma sintering (SPS) of vanadium boride powders were investigated starting from V₂O₅, B₂O₃ and Mg powders. Optimum synthesis conditions were determined by varying milling time and B₂O₃ or Mg contents. Powder specimens were examined by using XRD, SEM/EDX, TEM and HR-TEM. Influences of different methods on densification of the products were studied. Results showed that powders having the VB₂-VB-V₃B₄ phases were directly obtained without any intermediate phase and contamination by 7 h milling of the V₂O₅-B₂O₃-Mg powders with 50 wt% stoichiometric excess Mg and by subsequent leaching process. PS conducted at 1500 °C for 4 h was insufficient to achieve a high densification rate in the synthesized vanadium boride bulks. The final bulk product, relatively densified with a value of 90% and consisted of VB₂-VB-V₃B₄ phases in different proportions, was obtained by SPS at 1500 °C for 15 min. This nanostructured vanadium boride had a microhardness of 18 GPa and wear volume loss of 3.2 ×10^-4 mm³.