Study On Preparation And Toughening Mechanism Of Zirconia/Alumina Fiber Composites

The development of composite materials plays a negligible effect in the scientific and technological progress of the country.The researches and developments of ceramic matrix composites are the main component of the development of composite materials,and zirconia ceramic matrix composites are the most important.Zirconia ceramic matrix composites are widely used,but their inherent brittleness has great limitations on the application.Using single crystal sapphire fiber to improve the inherent performance defects of zirconia ceramics,makes it applied fully in various fields.In order to reaserch the preparation process and toughening mechanism of zirconia/alumina fiber composites,the single crystal sapphire fiber was prepared by Vapor-Liquid-Solid deposition mechanism.Use pressureless sintering and spark plasma sintering to prepare pure phase zirconia ceramics,and analyzed contrastively.The best sintering method and process parameters of pure phase zirconia ceramics were used to prepare zirconia/alumina fiber composites with different fiber contents.The effects of different fiber contents on zirconia/alumina fiber composites were analyzed and the toughening mechanism was explained.Single crystal sapphire fiber was prepared by Vapor-Liquid-Solid deposition mechanism.After high-temperature and vacuum purification,the obtained single crystal sapphire fiber has smooth surface,uniform thickness and large aspect ratio.The average diameter is about 500 nm.The main phase of the sapphire fiber is?-Al₂O₃ in a single crystal state before and after purification.?-Al₂O₃ belongs to the hexagonal system,and its main crystal planes are?104?,?110?and?006?.Pure phase zirconia ceramics were prepared by pressureless sintering and spark plasma sintering with different process parameters.The phase composition,microstructure,density,Vickers hardness and fracture toughness of the sintered products were compared.Finally,the best sintering process was spark plasma sintering.Sintering temperature is 1200°C.Sintering pressure is 50 MPa.The optimum pure phase zirconia ceramic`s density is 98.1%.The Vickers hardness is 14.46 GPa.The fracture toughness is 10.74 MPa·m^1/2.The zirconia/alumina fiber composites with different fiber contents were prepared by the above-mentioned optimal sintering method and process parameters.The phase composition,microstructure and comprehensive properties of the composites were compared and analyzed.The results show that the single crystal sapphire fiber is combined with zirconia ceramic successfully.When the fiber content is 5 wt%,the composite has the best performance.The density is 5.875 g/cm³.The relative density is98.8%.The Vickers hardness is 15.14 GPa and the fracture toughness is 12.24 MPa·m^1/2.The toughening mechanism existing in single crystal sapphire fiber toughened zirconia matrix composites mainly includes the stress-induced phase transformation toughening,the second phase whisker toughening and the fiber toughening.