| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 89 === The fracture toughness of zirconia is superior to other ceramics, and it is frequently used as a toughening agent to increase the fracture toughness of other brittle ceramics. In the present study, both alumina and silver particles are into zirconia (3Y-TZP) to enhance the mechanical properties of zirconia. Three systems: ZrO2/Al2O3, ZrO2/Ag and ZrO2/(Al2O3+Ag) composites, are prepared by pressureless sintering at 1600℃ for 1 hour.
A peculiar microstructure, abnormal ZrO2 grains are large pores, present in the zirconia matrix. From EPMA analysis, the abnormal grain growth of ZrO2 can be related to the non-uniformly distributed Y2O3. The alumina particles can be trapped into abnormal zirconia grains.
Apart from the pores and abnormal grains in zirconia matrix, adding silver into zirconia would also induce large pores due to the vaporization of silver and decomposition of the starting material of silver oxide.
On the other hand, the mechanical properties of zirconia indeed are affected by the inclusions. The elastic modulus of the zirconia composites matches the predictions from the rule of mixtures. Adding alumina increases the elastic modulus of zirconia; adding silver decreases the elastic modulus. The flexural strength of ZrO2/Al2O3, ZrO2 /Ag and ZrO2/(Al2O3+Ag) composites are dominated by the size of flaws, which are significantly larger than that of grain size. Adding alumina decreases the fracture toughness of zirconia; adding silver enhances the fracture toughness of zirconia due to the crack-bridge mechanism. From phase analysis, martensitic transformation of zirconia plays minor role on the increment of toughness.
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