| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 93 === The mechanical properties of ceramics can be enhanced by adding either metallic inclusions or ceramic particles. The extent of enhancement is closely related to the second phase content. In the present study, the amount of second phase added is lower than 5vol%. Two systems, ZrO2/Al2O3 and ZrO2/Ni composites are investigated.
Pressureless sintering technique was used to prepare the composites. The sintering temperature was 15000C (one-stage) and 16000C (two-stage) for ZrO2/Al2O3 system and 16000C for ZrO2/Ni system. The two-stage sintering technique provides better dimension control. The relative density of the ZrO2/Al2O3 composites after sintering is higher than 99%. But the relative density of ZrO2/Ni composites varies with the Ni content. The sintering atmosphere used in the present study, air vs. CO, may play an important role on the densification behavior of the composites.
The flexural strength was determined by using the 4-point bending technique. The strength of ZrO2/Al2O3 composites does not increase when a small amount of Al2O3 is added. The strength of ZrO2/Ni system depends strongly on the Ni content. The strength variation of ZrO2/Ni composites corresponds closely to their density variation. The fracture toughness was determined by using the single-edge-notched beam method. The similar results were obtained as that for strength. The mechanical properties of ZrO2/Al2O3 composites sintered at 16000C are superior to those of the ZrO2/Ni composites sintered at 16000C. But there is an increase of strength in ZrO2/Ni system as a small amount of 0.17vol%, is added. From the microstructural observation, the grain size was determined. The addition of Al2O3 affects little on the size of ZrO2 matrix grains. However, the addition of Ni particles also affect little on the grain size of ZrO2. Nevertheless, the mechanical properties are not affected by the grain size. It may be due to that the mechanical properties are over-shadowed by the influence of porosity.
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