Carbon nanofiber (CNF)-dispersed B₄C nanocomposites containing 2.5 vol% Al₂O₃ as a sintering aid were fabricated directly from mixtures of amorphous B and C, CNF, and Al₂O₃ powders by pulsed electric-current pressure sintering (PECPS) at 1800°C for 10 min under 30 MPa in a vacuum. Dispersion of CNF into the B₄C matrix up to ∼15 vol% introduced the enhancement of densification. A 15 vol% CNF/B₄C nanocomposite revealed excellent mechanical properties: a bending strength (σ_b) of ∼710 MPa, a Vickers hardness (H_v) of ∼36 GPa, and a fracture toughness (K_IC) of ∼7.6 MPa·m^1/2, in comparison with those (σ_b∼530 MPa, H_v∼29 GPa, and K_IC∼4.3 MPa·m^1/2) of monolithic B₄C.
Interfaces between CNF and B₄C matrix were investigated using high-resolution TEM and Eels. Thin Al-B-C-O layer with a several nm order thickness was observed along with CNF, and Eels showed that the densification and mechanical properties of CNF/B₄C nanocomposites might be related to this thin binding layer.