Yehong Cheng,Ping Hu,Shanbao Zhou,Xinghong Zhang,Wenbo Han
Graphene is one of the important candidates in ceramic toughening due to its outstanding physical and chemical properties. For the weak interface toughening of large-diameter graphene sheet and alleviation of the interfacial reaction between ceramic precursors and graphene sheets during high-temperature pyrolysis, ZrC–SiC‒Graphene composite was synthesized via a facile technology of infiltrating ceramic slurry instead of ceramic precursor into macroporous graphene network and spark plasma sintering . The incorporation of the graphene network improved fracture toughness, critical crack size, and fracture energy of ZrC–SiC ceramic. The multiple length-scale toughening mechanisms of ZrC–SiC‒Graphene composite include the macroscopic toughening mechanism of crack deflection and bifurcation and the micro toughening mechanism of graphene bridging, ceramic micro zone tearing, graphene pull-out, graphene and ceramic brick slipping.
Graceful toughness and high strength are mutually exclusive in engineering ZrC-SiC ceramic, which are hard to be possessed simultaneously. Here, the pyrolytic carbon (PyC) coated short chopped carbon fibers were utilized to toughen ZrC-SiC ceramic, tackling the dilemma between toughness and strength. Through the uniform incorporation of PyC coated short chopped carbon fibers, the penetration crack mode of ZrC-SiC was changed into an obviously deflecting propagation path with closed phenomenon. The PyC coating brought about a relatively weak interface bonding and guided the crack propagate along the weak interface, consequently resulting in a more flexuous crack propagation instead of passing through the fibers directly. Meanwhile, the fibers received effective protection of coating inhibiting from performance degradation. The PyC coated C f /ZrC-SiC obtained a fracture toughness highly reaching 7.57 ± 0.33 MPa m 1/2 with a rivaling flexural strength at 268 ± 16 MPa. Moreover, the graceful load-displacement curve is illustrated with a smoothly extended displacement of 0.12 mm and increased load to 83 N, which forms an obvious yield plateau. To some degree, this work provided an effective solution to tackling the dilemma between toughness and strength of engineering ZrC-SiC ceramic.
Yuan Cheng,Ping Hu,Wenzheng Zhang,Chen Ma,Jiaxin Feng,Qingpu Fan,Xinghong Zhang,Shanyi Du
The ZrC-SiC ceramics were introduced inside carbon fabric uniformly in one-step by vibration assisted injection. This novel method achieved a relative density of green body at 45%, nearly 50% higher than that of without vibration. The composite obtained a rivaling flexural strength at 185 ± 12 MPa, graceful fracture mode with fracture toughness at 5.86 ± 0.16 MPa∙m 1/2 and work of fracture reaching 1284 J/m 2 , 2 times of the value without vibration. By comparison, a poor fracture toughness and mediocre flexural strength of 4.05 ± 0.27 MPa∙m 1/2 and 113 ± 19 MPa are equipped with the non-vibration treated one.
In this work, porous ZrC-SiC ceramics with high porosity and low thermal conductivity were successfully prepared using zircon (ZrSiO 4 ) and carbon black as material precursors via a facile one-step sintering approach combining in-situ carbothermal reduction reaction (at 1600 °C for 2 h) and partial hot-pressing sintering technique (at 1900 °C for 1 h). Carbon black not only served as a reducing agent, but also performed as a pore-foaming agent for synthesizing porous ZrC-SiC ceramics. The prepared porous ZrC-SiC ceramics with homogeneous microstructure (with grain size in the 50–1000 nm range and pore size in the 0.2–4 µm range) possessed high porosity of 61.37–70.78%, relatively high compressive strength of 1.31–7.48 MPa, and low room temperature thermal conductivity of 1.48–4.90 W·m −1 K −1 . The fabricated porous ZrC-SiC ceramics with higher strength and lower thermal conductivity can be used as a promising light-weight thermal insulation material.
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