Directionally solidified large size ZrB₂–SiC eutectic composite ceramics with good mechanical properties by optical floating zone melting

ZrB₂–SiC eutectic composite ceramics with large size (Φ 6 mm × 15 mm) and near full density (≥99.5 %) were directionally solidified by optical floating zone melting (OFZM) for the first time. There exist some regularly arranged coarse eutectic bands among fine eutectic structure, which were probably formed by the movement of the melting pool during OFZM. Single-phase instability phenomenon featured by coarse primary ZrB₂phase and two-phase instability phenomenon featured by coarse eutectic dendrites among fine eutectic structure were observed at the edge and the middle of the molten pool, respectively. With increasing the pulling rate from 50 mm/h to 200 mm/h, the eutectic spacing decreases from 3.83 μm to 1.93 μm, which brings an slight improvement of Vickers hardness and fracture toughness. The good mechanical properties are attributed to many strengthening and toughening mechanisms such as crack branching, crack deflection, crack bridging, and multiple parallel crack initiation/propagation.