Microstructure and mechanical properties of ZrB₂-SiC eutectic composite ceramic fabricated by laser surface zone-melting: The effect of laser power and scanning speed

Directionally solidified ZrB₂-SiC eutectic composite ceramic with near-full density was rapidly prepared by laser surface zone-melting. The microstructure evolution and mechanical properties were discussed as a function of laser power and scanning speed. The eutectic microstructure was well refined with increasing the laser power (1100–1400 W) and scanning speed (5–250 µm/s), and it showed uniform labyrinthine Chinese script structure on the transverse section but changed from Chinese script to well-aligned lamellar structure on the longitudinal section. When the solidification rate improved from 50 µm/s to 250 µm/s, the eutectic spacing λ decreased from 2.8 µm to 1.2 µm in accordance with λv^1/2=19.4, which improved its Vickers hardness from 20.7 ± 1.8 GPa to 22.5 ± 0.7 GPa (increased by 8.7 %) and fracture toughness from 6.4 ± 0.3 MPa‧m^1/2 to 7.3 ± 0.4 MPa‧m^1/2 (increased by 14.1 %), respectively. Transgranular fracture was verified to be the primary fracture mode in ZrB₂-SiC eutectic composite ceramic. Besides, multiple toughening mechanisms were also observed in ZrB₂-SiC eutectic composite ceramic, such as crack bridging, crack deflection, crack branching, and multiple parallel crack initiation, which effectively enhanced the fracture toughness. This work gives a feasible route to regulate the eutectic microstructure and mechanical properties by adjusting the laser power and scanning speed.