Crucible-free fabrication of ZrB₂–SiC composite ceramics with ultra-fine eutectic microstructure by laser surface zone-melting: The selection of lasers

Here we report the crucible-free fabrication of ZrB₂–SiC composite ceramics by laser surface zone-melting (LSZM, a rapid solidification method) using Nd: YAG laser, ytterbium-doped fiber laser, and CO₂ laser, respectively. Based on the comparative investigation of the thickness and the microstructure of the laser processed zone, this work highlights that the CO₂ laser is the most suitable laser resource for the fabrication of highly dense and large-scale ZrB₂–SiC composite ceramics with the eutectic colonies consisting of maze-shaped eutectic microstructure by LSZM. The high temperature gradient up to ∼4 × 10⁵ K/m using CO₂ laser extremely reduces the phase size down to submicron-scale, which contributes to the high relative density (∼99%), Vickers hardness (24.18 GPa) and fracture toughness (7.4 MPa m^1/2) of the ZrB₂–SiC composite ceramics. This work demonstrates for the first time that LSZM is a promising method for the rapid fabrication of dense ZrB₂ based ultra-high temperature bulk ceramics.