氧化釔、氧化鈣、氧化鈰含量對鈦金屬與氧化鋯高溫擴散介面反應之影響

Abstract

以熱壓法製備不同組成之Y2O3/ZrO2複合材料，Y2O3固溶於ZrO2裡形成固溶體或者與ZrO2反應形成Zr3Y4O12。Y2O3/ZrO2複合材料與鈦金屬進行1700°C/10 min之熔融擴散反應後，發現於ZrO2中添加30 vol%以上的Y2O3對於鈦側的介面反應會有很好的抑制效果，鈦側反應物β'-Ti(Zr, O)形貌會變的非常細而且量非常少。於ZrO2內添加30 vol%以上的Y2O3，氧化鋯側靠近原始介面處發現有Y2O3的晶粒重新析出，原因為由鈦側沿著氧化鋯晶界進入此區域的Ti液固溶了大量的ZrO2，而Y2O3與Ti不會反應，使得原來熱壓30 vol% Y2O3-ZrO2陶瓷試片時固溶於ZrO2裡的Y2O3晶粒重新析出。在各組介面試片裡氧化鋯側遠離原始介面處皆發現有α-Zr之析出，生成量以10 vol%Y2O3最多，並且隨著Y2O3含量增加而減少，α-Zr析出的原因為ZrO2缺氧所致。

以熱壓法製備不同組成CaO-stabilized ZrO2，CaO固溶於ZrO2裡形成固溶體或者與ZrO2反應形成CaZr4O9。不同組成鈣安定氧化鋯與鈦金屬進行1550°C/6 h之固態擴散反應後，發現於ZrO2中添加5 mol%的CaO對於鈦側的介面反應有較好的抑制效果，原因為在鈦側有一層厚度約2 μm的TiO，此layer的形成可以有效阻擋Ti與Zr的相互擴散。而在9 mol% CaO與17 mol% CaO-ZrO2介面試片裡，由於Ti、O、Zr相互擴散劇烈的結果造成鈦側有α-Ti(O)、β'-Ti(Zr, O)和Ti2ZrO反應生成物，其中在17 mol% CaO-ZrO2的介面試片發現一層厚度較薄的(β'-Ti + α-Ti)。在9 mol% CaO與17 mol% CaO-ZrO2二組介面試片裡發現在氧化鋯側靠近原始介面處會有一層(β'-Ti + CaZrO3)，CaZrO3形成的原因為由鈦側擴散至此區域的Ti固溶了大量的ZrO2，CaO不與Ti反應而會維持在殘留的ZrO2基材中，使得氧化鋯基材CaO/ZrO2的比例漸漸提高至1:1而形成斜方晶相的CaZrO3。在17 mol% CaO-ZrO2介面試片裡，(β'-Ti + CaZrO3)為diffusion zone，CaZrO3的形貌為柱狀並且幾乎平行於O與Zr的擴散方向。在各組介面試片裡氧化鋯側遠離原始介面處皆發現有α-Zr析出於ZrO2-x晶界上，並且隨著CaO含量增加而減少。在17 mol% CaO-ZrO2介面試片裡，由於CaO固溶於ZrO2裡會產生較多異質的氧空孔，使得此區域的c-ZrO2-x為stable。

以粉末燒結法製備不同組成之CeO2/ZrO2系陶瓷材料，由於在高溫低氧分壓的環境下進行燒結，其中一部份的CeO2固溶於ZrO2裡形成固溶體或者與ZrO2反應形成Ce2Zr3O10，另一部份的CeO2則會還原成Ce2O3並且與ZrO2反應形成Ce2Zr2O7。Ce2Zr2O7是一個有氧空孔的結構，氧化鋯側的氧離子可以藉由氧空孔快速擴散至鈦側，因此在觀察不同組成之CeO2/ZrO2與鈦金屬進行1550°C/4 h之固態擴散反應後，發現30 mol% CeO2-ZrO2的試片與Ti的介面反應最為嚴重，原因為在這組介面試片裡，氧化鋯側靠近原始介面處會形成一層非常厚的(β'-Ti + Ce2Zr2O7)，Ce2Zr2O7的生成機構為由鈦側擴散至此區域的Ti對O與Zr有非常大的親和力，使得Ce2Zr3O10產生相變化所形成。在10 mol% CeO2-ZrO2介面試片裡，Ti側反應層的(α-Ti + Ti2ZrO)形貌與Y2O3/ZrO2及CaO/ZrO2二組系統有很大的不同，原因為Ce與Zr同為+4價，因此10 mol% CeO2固溶於ZrO2中並不會產生異質的氧空孔，而Y2O3與CaO固溶於ZrO2裡時因為異價陽離子的取代而產生較多異質的氧空孔，因此10 mol% CeO2-ZrO2的介面試片裡氧化鋯側氧離子擴散至鈦側的速度會比另外二組系統慢許多，因此造成(α-Ti + Ti2ZrO)靠近原始介面處析出。當ZrO2中添加CeO2的比例超過50 mol%時，發現氧化鋯側靠近原始介面處有secondary CeO2析出，其生成機構為高溫時Ce2Zr3O10分解成CeO2與ZrO2二相，而擴散至此區域的Ti固溶大量ZrO2形成α-Ti + β-Ti，因此cooling下來後使得secondary CeO2析出，實驗並發現CeO2添加的比例達到50 mol%時，鈦側只有α-Ti(O)，並無其它的反應層，其結果顯示由於secondary CeO2的析出可以有效阻擋氧化鋯側Zr離子往鈦側擴散，對於鈦側的介面反應會有較好的抑制效果。

Various Y2O3/ZrO2 samples were fabricated by hot pressing, whereby Y2O3 was mutually dissolved or reacted with ZrO2 as a solid solution or Zr3Y4O12. Hot pressed samples were allowed to react with Ti melt at 1700°C for 10 min in argon. Microstructural characterization was conducted using x-ray diffraction and analytical electron microscopy. The Y2O3/ZrO2 samples became more stable with increasing Y2O3 since Y2O3 was hardly reacted and dissolved with Ti melt. The incorporation of more than 30 vol% Y2O3 could effectively suppress the reactions in the Ti side, where only a very small amount of α-Ti and β'-Ti was found. When ZrO2 was dissolved into Ti on the zirconia side near the original interfaces, Y2O3 re-precipitated in the samples containing 30-70 vol% Y2O3, because the solubility of Y2O3 in Ti was very low. In the region far from the original interface, α-Zr, Y2O3, and/or residual Zr3Y4O12 were found in the samples containing more than 50 vol% Y2O3 and the amount of α-Zr decreased with increasing Y2O3.

ZrO2 samples with various CaO contents were fabricated by hot-pressing, whereby CaO was dissolved by and/or reacted with ZrO2 to form a solid solution and/or CaZr4O9, respectively. After a reaction with Ti at 1550°C for 6 h in argon, the interfacial microstructures were characterized using x-ray diffraction and analytical electron microscopy. Experimental results were very different from those previously found in the Y2O3-ZrO2 system. The 5 mol% CaO-ZrO2 sample was relatively stable due to the formation of a thin TiO layer acting as a diffusion barrier phase. However, □-Ti(O), β'-Ti(Zr, O) and/or Ti2ZrO were found in 9 or 17 mol% CaO-ZrO2 due to extensive interdiffusion of Ti, O, and Zr with a much thinner (□'-Ti + α-Ti) layer in 17 mol% CaO-ZrO2 than in 9 mol% CaO-ZrO2. Because CaO was hardly dissolved into Ti, it fully remained in the residual ZrO2, leading to the formation of spherical CaZrO3 in 9 mol% CaO-ZrO2 and columnar CaZrO3 in 17 mol% CaO-ZrO2. In the region far from the original interface, abundant intergranular α-Zr was formed in 5 or 9 mol% CaO-ZrO2. Scattered α-Zr and CaZrO3 were found in 17 mol% CaO-ZrO2 because a high concentration of extrinsic oxygen vacancies, which were created by the substitution of Ca+2 for Zr+4, effectively retarded the reduction of zirconia.

Ceramics with various CeO2/ZrO2 ratios were sintered at 1400ºC/4 h in air. The sintered bodies, consisting of CeO2, ZrO2, Ce2Ze3O10 and/or Ce2Ze2O7, were taken into reaction with Ti at 1550°C for 4 h in argon. Microstructural characterization was conducted using x-ray diffraction and analytical electron microscopy. Both dissolution and reaction-oxidation were the predominant mechanisms controlling the interface reactions. Because CeO2 was hardly dissolved into Ti, the CeO2/ZrO2 samples became more stable with increasing CeO2. The incorporation of more than 50 mol% CeO2 effectively suppressed the interfacial reactions in the Ti side without the formation of β'-Ti(Zr, O). In 10 mol% CeO2-ZrO2, selected dissolution of ZrO2 into Ti gave rise to the formation of a diffusion zone with a columnar shaped Ce2Zr3O10. In the 30-50 mol% CeO2-ZrO2 samples, Ce+4 was reduced to Ce+3 after reaction with Ti so that Ce2Zr3O10 was transformed into Ce2Ze2O7. Secondary CeO2 was re-precipitated at the interface between Ti and the samples containing 50-70 mol% CeO2. A reaction affected zone existed on the ceramic side far from the original interface due to the outward diffusion of oxygen. In the reaction affected zone, ZrO2 was reduced into α-Zr and ZrO2-x, while CeO2 was reduced into Ce2Zr2O7 and Ce2O3, depending upon the relative amounts of CeO2 and ZrO2. The effect of mass transport and contituent phases (e.g., CeO2 and Ce2Zr2O7) on the phase transformation in various reaction layers are elucidated.