Fabrication and characterization of FAST sintered micro/nano boron carbide composites with enhanced fracture toughness

Toughening of boron carbide (B₄C) without hardness degradation, was achieved by hierarchical structures consisting of B₄C micro-grains, titanium diboride (TiB₂) grains, and graphitic phases along B₄C grain boundaries. Such hierarchical structures were uniquely achieved by co-sintering of B₄C micro-powder and carbon-rich B₄C nano-powder, in situ formation of TiB₂, and by utilizing the short sintering time of field-assisted sintering technology. Toughening mechanisms observed after micro-indentation include crack deflection and delamination of graphite platelets, micro-crack toughening and crack deflection/bridging by TiB₂ grains. Fracture toughness enhancement was achieved while maintaining hardness: 4.65 ± 0.49 MPa m^1/2 fracture toughness and 31.88 ± 1.85 GPa hardness for a micro/nano B₄C-TiB₂ composite (15 vol% TiB₂ and 15 vol% B₄C nano-powders) vs. 2.98 ± 0.24 MPa m^1/2 and 32.46 ± 1.67 GPa for a reference micro B₄C sample. In future, macro-scale mechanical testing will be conducted to further evaluate how these micro-scale hierarchical structures can be translated to macro-scale mechanical properties.