Preparation And Sintering Performance Study Of ZrB₂/SiC Composite Powders

The fatal weakness of SiC ceramic is brittle, and the room temperature strength is low for SiC, making it subject to certain restrictions apply. Zirconium diboride(ZrB2), as an ultra-high temperature ceramic materials (UHTCs), has a combination excellent properties, such as high melting point, high hardness, high thermal and electrical conductivity and so on. ZrB2as the second phase particles added into SiC ceramic materials, can be guaranteed under the premise of their excellent performance, but improve the mechanical, thermal, electrical and other aspects of performance of SiC. In addition, the elastic modulus and coefficient of thermal expansion between ZrB2and SiC are different. Therefore, when ZrB2as the second phase particles add into SiC ceramic materials, the interface stress region will be formatied between the interface of ZrB2and SiC, then the crack advance will be blocked, or deflectied, bypassed and branched. Thus helping to improve the fracture toughness of the matrix material.First, Ultra-fine ZrB2/SiC composite powders have been synthesized by carbothermal reduction, and the process of synthesize composite powders conditions have been disscussed, then the composite powder phase composition and morphology of microstructure have also been analysed. The influence of synthesis temperature, holding time and reactant ratio on the phase composition, microstructure and particle size of ZrB2/SiC composite powders were investigated by X-ray diffraction and scanning electron microscope.The reaction mechanism of composite powders synthes-ized by carbothermal reduction has been investtigated in simply. The results show that the completeness of carbothermal reduction for the synthesis of ZrB2/SiC composite powders is needed of over dosage of boric acid (ZrO2:B2O3=1:1.5) when synthesized at1650℃for1h. The composite powders has an average particle size of less than0.5μm in different particle shape including whisker, rod and ball. With the increase of synthesis temperature, the whisker and rod particles gradually reduced while ball particles increase.At the same temperature, with the increase of holding time, also the whisker gradually reduced while ball particles increase, and the Larger particle size gradually accompany with combining more closely.Second, the ZrB2/SiC composite materials have been preparatied by pressureless sintering while using the micrometer commercial ZrB2and SiC powdes as raw materials, and be compared with Ultra-fine ZrB2/SiC composite powders have been synthesized by carbothermal reduction. The influence of formation pressure, the conten of effect sintering aids B4C-C and reactant ratio of ZrB2in composite materials on the densification and properties of ZrB2/SiC composite materials were investigated. The results show that, on the condition of the temperature about2200℃and the holding time is2h, the densification and properties of ZrB2/SiC composite materials were the best while the conten of effect sintering aids B4C-C are all about2wt%.With the briquetting pressure increase, the densification and properties became better, when the formation pressure be up to250MPa, flexural strength be up to highest.The interface of ZrB2and SiC may have oxide, such as ZrO2, B2O3and SiO2, et al. The oxidation film or borosilicate glass will be formationed while at the higher temperature in sintering process, thus, the densification of ZrB2/SiC composite materials will be hindered.But, when the Ultra-fine ZrB2/SiC composite powders have been synthesized by carbothermal reduction used as raw materials, the densification and properties of ZrB2/SiC composite materials are better.