Effects of Platelet TiB2 on the Formation and Mechanical Properties of (Zr,Ti)B2 Ceramics Prepared by Spark Plasma Sintering

(Zr,Ti)B2 ceramics with enhanced hardness and fracture toughness were prepared by spark plasma sintering using platelet TiB2 and irregular ZrB2 as starting powders. The effects of sintering temperature (1700–1900 °C) and platelet TiB2 content (0–30 wt.%) on the sinterability, phase composition, microstructure, and mechanical properties of the (Zr,Ti)B2 ceramics were investigated. With increasing sintering temperature, the relative density of the solid solution increased from 89.9 ± 0.5% at 1700 °C to 97.7 ± 0.4% at 1800 °C, followed by no significant change upon further temperature elevation; however, the relative density showed an initial increase and subsequent decrease with increasing TiB2 content. Under optimized parameters (1800 °C, 3 min, 50 MPa, with a TiB2 content of 30 wt.%), (Zr,Ti)B2 ceramics achieve a maximum hardness of 24.9 ± 1.0 GPa, a fracture toughness of 5.0 ± 0.3 MPa·m1/2, and a relative density of 96.5 ± 0.5%. The high content of platelet TiB2 refined the (Zr,Ti)B2 grain size, reducing the D50 by 25.8% to 1.70 μm compared to the 20 wt.% content. This study provides a novel perspective for the design and preparation of high-performance ceramics.