Effect of ball milling on simultaneous spark plasma synthesis and densification of TiC-TiB2 composites

The effect of ball milling pre-treatment of the starting Ti, B4C and C powders mixture on the synthesis of dense TiC/TiB2 composite was investigated through the combined use of a SPEX mill and the spark plasma sintering (SPS) apparatus. When unmilled reactants were used, amorphous carbon was converted to TiC through a combustion reaction with elemental titanium, while the complete conversion is achieved through a relatively slow reaction between the residual Ti and B4C. In contrast, powders ball milled for 24 h reacted completely under combustion regime. SPS product density was observed to increase from about 97% to 100% of the theoretical value, when the original powders were milled for 6 h, while further increase of the milling time led to a slight decrease in product density. Crystallite size of both boride and carbide phases decreased with milling down to about 50 nm after 24 h of mechanical treatment. The latter one also allowed for the formation of a material with relatively finer microstructure and more homogeneous phase distribution.