Synthesis and characterization of mechanical properties of boron–carbon-based superhard composites

Abstract

In this work, we investigated a modern combined processing technique for the synthesis of lightweight superhard composites based on boron–carbon. We used traditional B4C with precipitates of free graphite and Al powder as initial materials. In the frst stage, the composites were fabricated by the self-propagating high-temperature synthesis (SHS) with the subsequent hot pressing of the compound. Further, by the disintegration and attrition milling, the ultrafne-grained powder was obtained. We used HCl and HNO3 acids for the chemical leaching of the powder to remove various impure compounds. At the last stage, a solid composite was obtained by the spark plasma sintering (SPS) method under nitrogen pressure. The main feature of this approach is to implement diferent synthesis techniques and chemical leaching to eliminate soft phases and to obtain superhard compounds from low-cost materials. The phases were studied by X-ray difraction and scanning electron microscopy with energy-dispersive spectroscopy. The composites compacted by the SPS method contained superhard compounds such as B13C2, B11.7C3.3, and c-BN. The fabricated composite has an ultrafne-grained microstructure. Using a Berkovich indenter, the following nanohardness results were achieved: B13C2~ 43 GPa, c-BN~ 65 GPa (all in Vickers scale) along with a modulus of elasticity ranging between~400 GPa and~450 GPa.