Synthesis of Dense TiB₂‐TiN Nanocrystalline Composites through Mechanical and Field Activation

Abstract

The synthesis of dense nanometric composites of TiN-TiB 2 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 TiB 2 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 MPa⅐m 1/2 .

Reactive electric-discharge sintering of TiN-TiB2

“…The reactive consolidation of TiN-TiB 2 composites [26][27][28] permits producing materials over a wide range of compositions (from 6.13 to 52.90 wt.% TiB 2 ) with excellent mechanical properties: microhardness to 25 GPa and fracture toughness to 6.50 MPa ⋅ m 1/2 . The following chemical reactions occur when the final phase composition is being formed:…”

“…These methods are disadvantageous in that they additionally need dehydrogenation [26], prolonged grinding of the starting powders (to 25 h) [27], and high-pressure nitrogen [28].…”

“…This technique has the following advantages that facilitate the CCM production as compared with the methods described in [24][25][26][27][28]: brittle and grindable titanium dihydride can be used as a starting material, dehydrogenation and sintering processes can be combined, active metal titanium (dehydrogenation production) is an intermediate reagent, atomic hydrogen recombination and molecular hydrogen burning are used as an additional heating source, and hydrogen can be used as a protective medium.…”

“…Alloys based on TiN-TiB 2 can be produced by conventional sintering of TiN and TiB 2 powders [14,15,24], hot pressing [25], reactive hot pressing [26], and electric-discharge sintering [27,28]. Reactive consolidation methods rely on the mechanism of self-propagating high-temperature synthesis (SHS) in the Ti-N-B system.…”

Phase differentiation via combined EBSD and XEDS

“…A good example are multiphase materials such as titanium diboride and titanium nitride (Lee et al ., 2001) where the spectrum is a clutter of overlapping low-energy peaks of all three elements, as shown in Fig. 1, and it is difficult to discern the individual phases in the XEDS maps.…”