In situ synthesis, microstructure, mechanical properties and thermal shock resistance of (ZrB2 + SiC)/Zr2[Al(Si)]4C5 composites

• Novel (0–30 vol.%) (ZrB2 + SiC)/Zr2[Al(Si)]4C5 composites were designed and in situ prepared.
• In situ incorporated ZrB2 + SiC generate significant synergistic reinforcing–toughening effect.
• The composites show much improved modulus and could retain high modulus of 357 GPa at 1511 °C.
• The composites show much improved thermal conductivity (25–1200 °C) and thermal shock resistance.
• The composites exhibit promising prospect as candidate for ultra high-temperature ceramics.

Dense (ZrB2 + SiC)/Zr2[Al(Si)]4C5 composites with adjustable content of (ZrB2 + SiC) reinforcements (0–30 vol.%) were prepared by in situ hot-pressing. The microstructure, room and high temperature mechanical and thermal physical properties, as well as thermal shock resistance of the composites were investigated and compared with monolithic Zr2[Al(Si)]4C5 ceramic. ZrB2 and SiC incorporated by in situ reaction significantly improve the mechanical properties of Z2[Al(Si)]4C5 by the synergistic action of many mechanisms including particulate reinforcement, crack deflection, branching, bridging, “self-reinforced” microstructure and grain-refinement. With (ZrB2 + SiC) content increasing, the flexural strength, toughness and Vickers hardness show a nearly linear increase from 353 to 621 MPa, 3.88 to 7.85 MPa·m1/2, and 11.7 to 16.7 GPa, respectively. Especially, the 30 vol.% (ZrB2 + SiC)/Zr2[Al(Si)]4C5 composite retains a high modulus up to 1511 °C (357 GPa, 86% of that at 25 °C) and superior strength (404 MPa) at 1300 °C in air. The composite shows higher thermal conductivity (25–1200 °C) and excellent thermal shock resistance at ΔT up to 550 °C. Superior properties render the composites a promising prospect as ultra-high-temperature ceramics.