Abstract

Fully dense (Zr, Ti)C-(Ti, Zr)B2 composites were sintered via reactive pressureless sintering of ZrB2 and TiC based on the in-situ reaction and solid solution coupling effects. The effects of TiC content and sintering temperature on microstructure evolution and mechanical properties were explored. Elongated (Ti, Zr)B2 platelets were observed, stemming from the in-situ reaction between ZrB2 and TiC, and exhibited a high aspect ratio with the increase of TiC content. Besides, phase decomposition structures featuring semi-coherent interfaces were identified in the ZrB2-70mol.% TiC system sintered at 2200 °C, attributed to the chemical miscibility gap. High values of hardness (27.0 GPa), flexural strength (533 MPa), and fracture toughness (4.6 MPa m1/2) are found in ZrB2-70 mol.% TiC composite sintered at 2200 °C. The low porosity, solid solution strengthening, grain refinement caused by carbide phase decomposition, and high dislocation densities and strain concentration at the semi-coherent interfaces of carbide phase decomposed structures play an important role on hardening and strengthening. Furthermore, the presence of in-situ synthesized (Ti, Zr)B2 platelets with a high aspect ratio significantly contributes to toughening.

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