Effect of SiC content and particle size on pressureless sinteringbehavior and mechanical properties of ZrB۲-SiC composites

ZrB۲ is one of UHTC materials, with high melting temperature above ۳۰۴۰°C that hasunique properties. The highly covalent nature of bondings of these ceramics results insuperior mechanical properties such as hardness and strength and oxidation resistance. Zrbasedsystems were found to possess superior high-temperature oxidation resistance due toits high-melting point and low-vapor pressure of oxides and sub-oxides. The improvementin properties is making these ceramics suitable for use in thermal protection systems. In thepresent paper, ZrB۲-SiC composites were prepared by pressureless sintering attemperatures of ۲۰۰۰-۲۲۰۰°C for ۱ h under argon atmosphere. In order to preparecomposite samples, ZrB۲ powder was milled for ۲ h, then the reinforcing particlesincluding of micron and nano-sized SiC powder were added. The mixtures were formedand, after the pyrolysis, they were sintered. Desification, microstructural and mechanicalproperties of ZrB۲-SiC composites were investigated. The shrinkage of samples wasmeasured both before and after the sintering, and the microstructure of samples wasexamined using scanning electron microscopy (SEM), equipped with EDS spectroscopy.Both mass fraction and size of SiC powder have a great effect on relative density, porosity,shrinkage, hardness and microstructure of these composites. The highest relative densityand hardness were ۹۸.۱۲% and ۱۵.۰۲GPa, respectively, in ZrB۲-۱۰wt%SiCnano compositesintered at ۲۲۰۰°C.

کلیدواژه ها:

ZrB۲-SiC composites ، Pressureless sintering ، Microstructure ، Mechanicalproperties