微量添加氧化鈮對釔安定氧化鋯複合材料之相穩定及機械性質之影響

Abstract

以3 mol%氧化釔安定之氧化鋯(3YSZ)具有優異的機械性質，如高強度及高韌性等。近年來在3YSZ中加入20wt%的氧化鋁(Al2O3)粉也因為其具有優秀的強度及熱穩定性而被廣泛應用。本研究將微量(0-2 mol%)的氧化鈮(Nb2O5)加到3YSZ及3YSZ/20wt%Al2O3中。試樣在空氣氣氛中進行燒結，持溫時間為一小時。本研究探討了添加氧化鈮對於相穩定性、微結構、機械性質、以及熱傳導性質的影響。 結果顯示當添加0.5 mol %氧化鈮時，3YSZ及3YSZ/20wt%Al2O3的破壞韌性將大幅度增加。當氧化鈮含量增加時，在試樣中的正方相氧化鋯將變得不穩定。不穩定的正方相氧化鋯易發生相變化，而伴隨的相變化增韌機制，使此兩氧化鋯系統的破壞韌性的提升。其他機械性質如強度以及硬度在本系統中並沒有隨著微量氧化鈮的添加而有明顯的變化。 3YSZ/20wt%Al2O3/Nb2O5相較於3YSZ/Nb2O5表現出較高的強度和韌性。強度以及韌性的增加源於3YSZ/20wt%Al2O3中的殘餘應力。

The 3 mol% Y2O3-stabilized zirconia (3YSZ) exhibits excellent mechanical properties such as high strength and high fracture toughness. Recently, 3YSZ/20wt%Al2O3 powder has also been widely used for its excellent strength and thermal stability. In the present study, a small amount (0-2 mol%) of niobium oxide (Nb2O5) was added into 3YSZ and 3YSZ/20wt%Al2O3 systems. The specimens were sintered at 1600°C in air for 1 hour. The effect of Nb2O5 addition on the phase stability, microstructure, mechanical properties and thermal conductivity was then investigated. The results indicate that the fracture toughness is increased significantly after the addition of 0.5 mol % Nb2O5 both in the 3YSZ and in 3YSZ/20wt%Al2O3 systems. The tetragonal ZrO2 phase in the composites becomes unstable as the Nb2O5 content is high. The instability of tetragonal ZrO2 promotes its transformability, it results in the phase transformation from tetragonal phase to monoclinic phase. The toughening mechanism induces the increase of fracture toughness in the zirconia systems. Other mechanical properties such as strength and hardness remain the same after the addition of a small amount of Nb2O5. The 3YSZ/20wt%Al2O3/Nb2O5 specimens exhibit higher flexural strength and higher fracture toughness comparing to those of the 3YSZ/Nb2O5 specimens. The increase of flexural strength and fracture toughness may be related to the presence of residual stress in the ZrO2-Al2O3 systems.