Effect of ball milling on reactive spark plasma sintering of B4C–TiB2 composites

The influence of mechanical activation by ball milling (BM) of Ti, B and graphite powders mixture on the synthesis of dense B4C-41% vol. TiB2 composite by Spark Plasma Sintering (SPS) is investigated. BM treatment produces grains size refinement (50–150 nm) in the processing powders and the formation of TiB and TiB2, when milling times are longer than 6 h. The synthesis process occurs through a solid-state diffusion mechanism where the first crystalline phase formed is TiB, which is gradually converted to TiB2, while the formation of B4C takes place subsequently. The complete conversion of unmilled reactants is reached at about 1500 °C, while this goal is achieved at 1100 °C when using 3 h milled powders. A near to fully dense product with fine grained microstructure (down to submicrometer level) and homogeneous phases distribution is obtained by SPS when starting from 8 h milled powders, if the applied current intensity does not overcome 1150 A.