Abstract
High toughness and high hardness Si3N4 ceramics with fine and bimodal microstructure was prepared by combination of HfB2 additive and spark plasma sintering (SPS). HfB2-free SPSed Si3N4 ceramics at 1600 °C exhibited major α-Si3N4 phase, a fine and equiaxed grain microstructure, high Vickers hardness (21.3 ± 0.2 GPa), and low fracture toughness (3.7 ± 0.3 MPa m1/2). The introduction of 2.5 vol% HfB2 into Si3N4 ceramics at 1600 °C promoted α-to β-Si3N4 phase transformation, produced a fine and bimodal microstructure, significantly improved the toughness (7.7 ± 0.6 MPa m1/2) but slightly decreased the hardness (20.4 ± 0.6 GPa) which was higher than that of traditionally hot-pressed or pressurless sintered Si3N4 ceramics (~14–18 GPa).
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