添加氧化鎳對釔安定氧化鋯/氧化鋁複合材料之燒結行為及機械性質研究

Abstract

3mol%Y2O3-stabilized ZrO2/20wt%Al2O3 (YSZ/Al2O3)係藉由20wt%Al2O3第二相散佈於3YSZ中，所發展的陶瓷基複合材料，展現了相當優異的機械性質。已知ZrO2的微結構及相穩定性和添加之溶質有相當的關係，本研究係藉由添加微量NiO，控制ZrO2的微結構以及相變化，更進一步提升YSZ/Al2O3的機械性質。利用無壓燒結YSZ/Al2O3/NiO複合材料，在1600°C可達緻密化，再研究NiO的添加對於複合材料之相變化、微結構以及機械性質的影響。另外，也進行了微量NiO對於YSZ/Al2O3熱傳導性質的研究。 本研究中，Ni2+固溶於ZrO2晶格中，幫助了YSZ和YSZ/Al2O3複合材料的燒結緻密化。對於ZrO2高溫相(立、正方晶相)的穩定性而言，除了複合材料中內含的Y2O3以外，NiO可作為額外的穩定劑，固溶至ZrO2之晶格中進行原子置換，促使氧空缺的生成，幫助高溫相的穩定。然而，在燒結時，NiO可影響Y2O3在ZrO2中的重新分配，更進一步影響了正方晶相ZrO2的穩定性。另外，研究發現，NiO微量添加並固溶於晶格中，可以幫助YSZ/Al2O3複合材料的晶粒成長。在相穩定性以及晶粒大小的改變下，NiO的添加，確實可以更進一步地提升YSZ/Al2O3複合材料的機械性質。

Some ceramic matrix composites exhibit excellent mechanical properties. The 3mol% Y2O3-stabilized ZrO2/20wt%Al2O3 (YSZ/Al2O3) composite is one of these composites. To further enhancement the mechanical properties of ceramics, the formation of solid solution could be employed to control the microstructure and phase transformation of ZrO2. In the present study, a small amount of NiO was added into YSZ/Al2O3 composite as a second stabilizer to increase the concentration of oxygen vacancies. The YSZ/Al2O3/NiO composites were then prepared using the pressureless sintering at 1600°C to achieve full densification. Several analyses were conducted to investigate the influence of NiO addition on the phase transition and microstructure evolution. The fracture toughness and flexural strength of YSZ/Al2O3/NiO composites were then evaluated. Furthermore, the thermal conductivity of composite was determined. The Ni2+ ion could act as a sintering-aid, promoting the densification of YSZ and YSZ/Al2O3 composite. It is found that NiO not only provides extra oxygen vacancies but also increases the redistribution of Y2O3 during sintering. The phase stability of ZrO2 is thus affected. The grain growth of YSZ/Al2O3 composite could also be promoted by the addition of Ni2+ solutes. Because the microstructure and phase stability is affected significantly, the mechanical properties could be further enhanced through the addition of a small amount NiO.