Preparation and characterization of ZrB2–SiC–Zr2Al4C5 composites by spark plasma sintering-reactive synthesis (SPS-RS) method

ZrB2–SiC–Zr2Al4C5 composite ceramics were fabricated in situ by the spark plasma sintering technique using B4C/Zr/Si/C/Al powders at 1800 °C for 3 min under 20 MPa in a vacuum atmosphere. The Zr–Al–C layered phase incorporated into the ZrB2–SiC–Zr2Al4C5 composites improved the sinterability, microstructure and mechanical properties of the composites. As the content of Zr–Al–C increased, both of Vicker's hardness and fracture toughness of composites firstly increased and then decreased, and Young's modulus decreased linearly. The composite with 20 vol% Zr–Al–C showed optimized microstructure and the best performance, and its fracture toughness value was 5.31 MPa m1/2, which was about 30% higher than that of the ZrB2–SiC ceramic. The improvement mainly attributed to the layered phase toughening and the homogeneous distribution of in situ formed Zr–Al–C phases. The fracture mode exhibited a mixture of inter- and intra-granular fractures, and the toughening mechanisms were the laminated Zr–Al–C grains toughening, crack deflection and crack bridging. With further increase in Zr–Al–C content up to 40 vol%, the grain size of ZrB2 and Zr–Al–C increased remarkably, and the transgranular fracture of Zr–Al–C and ZrB2 grains led to a worse in mechanical properties.