Effect of ZrB2 content on phase assemblage and mechanical properties of Si3N4–ZrB2 ceramics prepared at low temperature

Based on the previous work on Si 3 N 4 –ZrB 2 [Wu et al. J Eur Ceram Soc ;2017,37:4217], the influence of ZrB 2 addition on the phase and microstructure evolution of Si 3 N 4 –ZrB 2 composites was emphatically investigated, and the mechanical properties were compared with pure Si 3 N 4 ceramics. It was revealed that the ratio of β- to (α+β)-Si 3 N 4 significantly increased from 14.3% in pure Si 3 N 4 ceramics to 39.8% in Si 3 N 4 with 15 vol% ZrB 2 addition, indicating that the introduction of ZrB 2 promoted α- to β-Si 3 N 4 phase transformation. As a consequence, the microstructure of the composite showed the bimodal distribution, containing both elongated and equiaxed Si 3 N 4 grains. For the pure Si 3 N 4 , Vickers hardness, fracture toughness and flexural strength was 22.8 GPa, 7.6 MPa m 1/2 , and 334.5 MPa, respectively. In contrast, the composite of Si 3 N 4 –30 vol% ZrB 2 simultaneously possessed an excellent combination of mechanical properties: 19.5 GPa in hardness, 9.8 MPa m 1/2 in toughness and 702.0 MPa in strength. Present study suggested that Si 3 N 4 -based ceramics with high hardness, high toughness, and high strength could be obtained by the combination of appropriate ZrB 2 content and low hot-pressing temperature.