In situ synthesis, microstructure, mechanical properties and thermal shock resistance of (ZrB_2 + SiC)/Zr_2[Al(Si)]_4C_5 composites

摘要

Dense (ZrB_2 + SiC)/Zr_2[Al(Si)]_4C_5 composites with adjustable content of (ZrB_2 + 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 Zr_2[Al(Si)]_4C_5 ceramic. ZrB_2 and SiC incorporated by in situ reaction significantly improve the mechanical properties of Zr_2[Al(Si)]_4C_5 by the synergistic action of many mechanisms including paniculate reinforcement, crack deflection, branching, bridging, "self-reinforced" microstructure and grain-refinement. With (ZrB_2 + 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-m~(1/2), and 11.7 to 16.7 GPa, respectively. Especially, the 30 vol.% (ZrB_2 + SiC)/Zr_2 [Al(Si)]_4C_5 composite retains a high modulus up to 1511℃ (357 GPa, 86% of that at 25℃) and superior strength (404 MPa) at 1300℃ in air. The composite shows higher thermal conductivity (25-1200℃) and excellent thermal shock resistance at ΔT up to 550℃. Superior properties render the composites a promising prospect as ultra-high-temperature ceramics.