Fabrication of SPS compacts from NbC–NbB2 powder mixtures synthesized by the MA–SHS in air process

When the powder mixture of Nb/B/C = 2/2/1 in molar ratio was mechanically activated (MA) by ball milling for 105 min and then exposed to air, it self-ignited spontaneously and the self-propagating high-temperature synthesis (SHS) was induced. The powder mixture of NbC and NbB2 was obtained by this MA–SHS in air process and then sintered by spark plasma sintering (SPS) at a temperature as low as 1800 °C. The sintered NbC/NbB2 composite compact showed the fine, homogeneous microstructure consisting of the a few μm-sized grains and the Vickers hardness of 19.8 GPa, which was higher than 14.3 and 16.6 GPa for the NbC/NbB2 composite compacts sintered from the powder mixture of Nb/B/C = 2/2/1 without MA–SHS and from the commercial powder mixture of NbC/NbB2 = 1/1.