Bio-inspired structured boron carbide-boron nitride composite by reactive spark plasma sintering

Abstract

Nature creates composite materials with complex hierarchical structure that possesses impressive mechanical properties enhancement capabilities. An approach to improve mechanical properties of conventional composites is to mimic biological material structured ‘hard’ core and ‘soft’ matrix system. This would allow the efficient transfer of load stress, dissipate energy and resist cracking in the composite. In the current study, reactive spark plasma sintering (SPS) of boron carbide B4C was carried out in a nitrogen N2 gas environment. The process created a unique core-shell structured material with the potential to form a high impact-resistant composite. Transmission electron microscopy observation of nitrided-B4C revealed the encapsulation of B4C grains by nano-layers of hexagonal-boron nitride (h-BN). Effect of the h-BN contents on hardness were measured using micro- and nano-indentation. Commercially available h-BN was also mechanically mixed and sintered with B4C to compare the effectiveness of nitrided B4C. Results have shown that nitrided B4C have higher hardness value and the optimum content of h-BN from nitridation was 0.4%wt with the highest nano-indentation hardness of 56.7GPa. The high hardness was attributed to the h-BN matrix situated between the B4C grain boundaries which provided a transitional region for effective redistribution of the stress in the material.