Synthesis of dense TIB2-TIN nanocrystalline composites through mechanical and field activation

The synthesis of dense nanometric composites of TiN-TiB2 by mechanical and field activation was investigated. Powder mixtures of Ti, BN, and B were me chanically activated through ball milling. Some powders were milled to redu ce crystallite size but to avoid initiating a reaction. In other cases powd ers were milled and allowed to partially react. All these were subsequently reacted in a spark plasma synthesis (SPS) apparatus. The products were com posites with equimolar nitride and boride components with relative densitie s ranging from 90.1% to 97.2%. Crystallite size analyses using the XRD trea tments of Williamson-Hall and Halder-Wagner gave crystallite sizes for the TiN and TiB2 components in the range 38.5-62.5 and 31.2-58.8 nm, respective ly. Vickers microhardness measurements (at 2 N force) on the dense samples gave values ranging from 14.8 to 21.8 GPa and fracture toughness determinat ions (at 20 N) resulted in values ranging from 3.32 to 6.50 MPa .m(1/2).