A novel ZrB2-C3N4 composite with improved mechanical properties

摘要

In this research, a novel application for graphitic carbon nitride as the sintering aid and reinforcement was investigated. In this regard, g-C3N4 doped ZrB2-based ultrahigh temperature ceramic was fabricated by route of spark plasma sintering at 1850 degrees C under an applied pressure of 40 MPa for 6 min. Microstructure development, sinterability, and mechanical properties were studied and compared to the additive-free ZrB2. The sinterability was remarkably enhanced, and a fully-dense ceramic was obtained by addition of 5 wt% g-C3N4, in comparison with the monolithic ZrB2 with a relative density of 76.5%. The elimination of oxide surface impurities of ZrB2 (B2O3 and ZrO2) through chemical reactions with g-C3N4 and the formation of in-situ phases like ZrC and BN were confirmed by microstructural and phase analyses. Mechanical properties were enhanced with a small amount of g-C3N4 additive due to the densification improvement and prevention of grain growth. The values of hardness, indentation fracture toughness and flexural strength increased from 10.1 GPa, 1.9 MPa m(1/2) and 187.6 MPa for monolithic ZrB2 to 16.2 GPa, 5.4 MPa m(1/2) and 516.4 MPa for g-C3N4 doped ZrB2 ceramic.