Comparative study of sintered and eutectic ZrB2–SiC composites: Hardness, micro-scale fracture behavior, and interfacial effects

ZrB2–SiC pseudo-binary composites were prepared using three distinct methods: spark plasma sintering (SPS), laser melting (LM), and arc melting (AM). The composites produced by SPS exhibited densely sintered microstructures, whereas those produced by AM exhibited typical eutectic microstructures. Both sintered and eutectic microstructures were observed in the composites prepared using LM. Nanoindentation test results indicated that the eutectic microstructures exhibited enhanced fracture toughness. In the sintered microstructure, the cracks propagated predominantly along the interfaces. In contrast, in the eutectic microstructure, the cracks tended to traverse the grain interior. The interfacial microregions exhibited intermediate hardness between those of the individual components of the sintered microstructure. However, in the eutectic microstructure, the hardness of the interfaces was comparable to that of SiC, suggesting that hardening occurred owing to dislocation accumulation in ZrB2 at the eutectic interfaces. These results demonstrate that the suppression of interfacial crack propagation at eutectic interfaces compared to sintered interfaces can be attributed to the enhanced plasticity of ZrB2 and interface strengthening via work hardening, which contribute to the overall higher fracture toughness of the eutectic microstructure.