We report on the growth and characterization of 4mm diameter x50mm long boron carbide (B4C) single crystals using a laser diode floating zone (LD-FZ) method. Electron micro-structure analysis shows the presence of a significant number of twinning-boundaries along the growth direction (h) oriented in the h plane. Faster growth rates tended to reduce the number of twins seen. Zone refinement of these crystals led to a significant reduction of trace impurities at the expense of increased twinning. Powder x-ray diffraction confirms that the bulk is rhombohedral B4C, as shown by the micro-structure. Berkovich nano-indentation of the key h plane showed 41 +/- 1 GPa hardness, with a Young’s modulus of 520 +/- 14 GPa, like the other planes measured in the literature.
