Ultrafine Al2O3–B4C composites consolidated by pulsed electric current sintering

Al2O3–60 vol.% B4C composites with 0–5 wt% SiC addition were consolidated by pulsed electric current sintering (PECS) during 4 min at 1650 °C. The influence of the SiC additive on the densification behaviour, microstructure and mechanical properties of the Al2O3–B4C composites were investigated. Microstructural analysis revealed the presence of Al18B4O33 grains, formed by chemical reaction of Al2O3 with surface oxides on B4C, in agreement with thermodynamic calculations. The Al2O3 grains were found to coarsen from 0.22 μm in the starting powder up to about 0.60 μm during PECS, whereas the size of the ∼0.6 μm B4C grains hardly changed. The Al2O3 and B4C grain size slightly decreased upon SiC addition. The addition of 3 or 5 wt% SiC hardly influenced the hardness and toughness of the Al2O3–B4C composites, whereas the strength and stiffness were reduced. The composite with 1 wt% SiC combined a hardness of 26 GPa, an E-modulus of 448 GPa, a bending strength of 600 MPa and a fracture toughness of 6.2 MPa m1/2. The influence of the loading condition and dwell time during PECS of the 5 wt% SiC doped composite was assessed.