Microstructures and mechanical properties of reactive spark plasma-sintered ZrB2–SiC–MoSi2 composites

Ternary ZrB 2 –SiC–MoSi 2 composites with different nominal volume fractions of SiC (10–25 vol%) and MoSi 2 (5–20 vol%) were sintered by reactive spark plasma sintering (RSPS) at 1650 °C and 35 MPa from the starting powders of ZrB 2 , Si, Mo and activated charcoal. The densification behaviour, microstructures and mechanical properties were comprehensively investigated. SiC clusters and MoSi 2 were formed by in-situ reactions and the improved sintering efficiency was attributed to the mass transfer by liquid Si. The formation of a core–shell (Zr, Mo)B 2 solid solution was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the addition of the nominal MoSi 2 content up to 15 vol%, the molar ratio of MoB 2 in the solid solution shell increased owing to the increase of Mo; the densification and mechanical properties decreased owing to the softness of MoSi 2 , the cracks, and the large size of SiC clusters. The relative density, Vickers hardness , and fracture toughness of ZrB 2 –SiC–MoSi 2 composites were significantly better than those of bulk ZrB 2 owing to the combined effect of phase enhancement and solid solution strengthening.