Preparation And Mechanism Of Strengthen And Toughening Of Al₂O₃/ZrO₂ Ceramics Compounds

The ZrO₂ matrix nano-ceramic composites were fabricated by hot press sintering using nano- ZrO₂ powders. The microstructures were analyzed by means of XRD, SEM, EDS and so on. The effect of the second phases Al₂O₃ and SiC particles on the mechanical properties and microstructure of ZrO₂ nano-ceramics were investigated, and the reinforced and toughening mechanism were discussed.First of all, based on the introduction of microstructure, development of ZrO₂ based ceramics, fabrication methods and sintering methods, the content and significance of this thesis were indicated. Second, fabrication techniques, testing methods of mechanical properties and observing methods of microstructure of nano-ZrO₂ matrix ceramic composites were introduced.The research results showed that composite powders of Al₂O₃/ZrO₂ can be well dispersed after being ultrasonically dispersed with dispersant agent of PHAA-NH4 and wet ball milled. The second phase Al₂O₃ dispersed homogeneously in the matrix grains. The second phase Al₂O₃ inhibited matrix grains growth, i.e. the ratio of grains is inverse proportion to the amount of Al₂O₃, but excessive amount of Al₂O₃ causes grains agglomeration decreasing the density. When the amount of doped-Al₂O₃ was 9mol%, the relative density, hardness and flexure strength of composite ceramics reached the maximum; but fracture toughness arrived crest value when doped-Al₂O₃ was 12mol%. The matrix ZrO₂ grains were refined after adding Al₂O₃ and SiC, which induced fracture model to change from intergranular fracture to transgranular fracture.It was analyzed from SEM photos that many toughening mechanisms played roles in composite ceramics material. Firstly, the second phase Al₂O₃ which located at grain boundary refined matrix grains as a result of pinning effect. Secondly, the second phases Al₂O₃ induced crack deflection and bridging crack obviously, which Al₂O₃ grains shape played a very important role in performance improvement. Thirdly, transgranular microstructure formed when Al₂O₃ entered matrix grains. The formation of this microstructure has direct relationship with sintering temperature and second phase's grain diameter. Transgranular fracture became the chief fracture model because that difference of thermal expansion coefficient between Al₂O₃, SiC and matrix ZrO₂ exerted compression stress on matrix and reinforced grain boundary. Those mechanics increased fracture toughness of composite ceramics.