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 mechanically activated through ball milling. Some powders were milled to reduce crystallite size but to avoid initiating a reaction. In other cases powders were milled and allowed to partially react. All these were subsequently reacted in a spark plasma synthesis (SPS) apparatus. The products were composites with equimolar nitride and boride components with relative densities ranging from 90.1% to 97.2%. Crystallite size analyses using the XRD treatments 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, respectively. Vickers microhardness measurements (at 2 N force) on the dense samples gave values ranging from 14.8 to 21.8 GPa and fracture toughness determinations (at 20 N) resulted in values ranging from 3.32 to 6.50 MPa·m^1/2.