Nanocrystalline TiB 2 is prepared by reaction of NaBH 4 and TiCU. The initial solution-phase reaction affords an amorphous precursor powder from which 5-100 nm TiB 2 crystallites are obtained upon annealing at 900-1100 °C. Crystallite sizes depend on the annealing temperature and other processing parameters. Crystallite morphology is size dependent; crystallites smaller than 12-15 nm are cuboidal, whereas crystallites larger than 12-15 nm are hexagonal platelets. The procedure affords gram quantities of the smallest available TiB2 nanocrystallites.

Nanocrystalline copper powder was produced by a NaBH4 reduction of CuCl in a simple solution phase room temperature reaction. Uniaxial hot pressing in a closed tungsten die was used to compact powder into dense specimens. Samples were analyzed by x-ray diffraction, precision densitometry, electron microscopy, energy dispersive x-ray analysis, and selected area diffraction. Mechanical properties of the consolidated samples were determined by microhardness measurements, three-point bending of rectangular specimens, and compression tests. Yield strength measured for nanocrystalline Cu in the present work was over two times that reported in literature for Cu with comparable grain size and over five times that of conventional Cu. Restricted grain growth observed in the hot-pressed samples and improved mechanical properties are attributed to the presence of boron. A unique method of obtaining homogeneous in situ nanosized reinforcements to strengthen the grain boundaries in nanocrystalline materials is identified.

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