Preparation, microstructure, and mechanical properties of ZrB2-based ceramics with layered Zr2Al4C5 inclusions

ZrB2/Zr2Al4C5 composite ceramics with different volume contents of Zr2Al4C5 formed in situ were fabricated by the spark plasma sintering technique at 1800 °C. The content of Zr2Al4C5 was found to have an evident effect on the preparation, phase constitution, microstructure as well as the mechanical properties of ZrB2/Zr2Al4C5 ceramics. The results indicated that sinterability of the composites was remarkably improved by the addition of Zr2Al4C5 compared to the single-phase ZrB2 ceramic. The microstructure of the resulting composites was fine and homogeneous, the average grain size of the ZrB2 decreased, and the average aspect ratio of the Zr2Al4C5 increased with the increase in the amount of Zr2Al4C5. As the content of Zr2Al4C5 increased, both the Vickers hardness and Young's modulus of the composites first increased and then decreased. The fracture toughness of the ZrB2-40 vol% Zr2Al4C5 composite was 4.25 MPa m1/2, which increased by approximately 70% compared to the monolithic ZrB2 ceramic. The improvement was mainly attributed to the toughening mechanisms such as the layered structure toughening, crack deflection and crack bridging, caused by the in situ formed layered Zr2Al4C5 inclusions.