| In this paper,TiB2-TiCo s/xSiC multiphase ceramics containing different contents of SiC are fabricated with TiH2,SiC and graphite powders by in-situ synthesis under hot pressing(HP) with different temperatures. The preparation process and performances have been studied.TiB2-TiCo s/SiC composite samples consisting of10、20、30mol SiC are full dense and the relative densities are beyond99.8%. TiB2-TiC0.8SiC composites under HP consisting of10mol SiC, in the way, are full dense,microstructure indicate black SiC, gray lumps TiC0.8,gray strip TiB2. As SiC added over20mol, densification required temperature is2100℃under hot pressing.High densified TiB2-TiC0.8-SiC multiphase ceramics and optimized microstructure is obtained by sintering at1900℃, in which the Vickers hardness, fracture toughness, flexural strength and electrical conductivity of the TiB2-TiC0.8-SiC multiphase ceramics sintered at1900℃are23.6GPa,7.0±1.0MPa-m1/2,470.9MPa and2.2-2.5×106S·m-1, respectively. While the ceramic material was pre-treatment by cold isostatic pressing(CIP) fracture toughness and bending strength further increased to8.3±1.0MPa·m1/2,516.69MPa. TiB2, TiC0.8and SiC particles were incorporated to improve the particulate strength and toughness of composite material by the synergistic action of the mechanisms such as crack deflection, grain’s pull-out and fine-grain toughening.TiB2-TiCo.s/SiC multiphase ceramic material has excellent antioxidant properties.The curves of isothermal kinetics of the TiB2-TiC0.8/SiC multiphase ceramics obey parabolic oxidized law or parabolic-liner oxidized law.With the increase of SiC content,the oxidation resistance of composite ceramics gradually increase. In the state, the different SiC content of the oxide layer composite ceramic material is divided into two layers.Two-layer oxide film is formed as the inner layer of TiO2and SiO2buffer layer film,the outer layer is glassy TiO2and B2O3.In the high temperature, with the increase of SiC content, the oxide layer that is gradually evolving.that is a protection of the membrane surface by the pure SiO2film into amorphous boron silicate glass complex.This indicates that a sufficient amount of SiC phase can protect the body effectively.High temperature oxidation resistance of SiC, blunt oxidation of borosilicate glass blunt and uniform internal stress in the composite are incorporated to improve the excellent oxidation resistance properties. During the block-on-ring type test, TiB2-TiCo.s/SiC multiphase ceramic is dominated by abrasive wear at low speeds. And accompanied by a small amount of oxidation wear and slight adhesive wear.High-speed, complex phase ceramic is mainly adhesion wear with a small amount of oxidation wear and abrasive wear, then extruded debris lubricating film formed denser complete, with good anti-friction effect, so the friction factor appeared reduced. Speed is constant.as the load increases, the multiphase ceramic material is formed by a low load of abrasive wear into the wear mechanism based adhesive and oxidation wear mechanism supplemented.In the fatigue test of TiB2-TiC0.8/SiC multiphase ceramic material, fatigue behavior of TiB2-TiCo.s/SiC multiphase ceramics is very unstable, presents the obvious uncertainty. Composite ceramics at room temperature cycles107weeks times and the fatigue limit is323MPa-366MPa.Fatigue strength of TiB2-TiC0.8/SiC composite ceramics has no crack source in low cycle, almost completely brittle fracture,is very similar with the bending fracture morphology.In high cycle,the material cracks source is located at the corners.With the increase of the number of cycles, gradually along the sintering defects (holes) link called the main crack and break.TiB2, TiCos and SiC particles are incorporated to improve bending, fatigue strength via the particulate strength and toughness of composite material by the synergistic action of the grains pull-out and fatigue occurs intergranular, intragranular fracture mechanisms. |
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