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 degrees 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 degrees C for 15 min. This nanostructured vanadium boride had a microhardness of 18 GPa and wear volume loss of 3.2 x 10(-4) mm(3).