鈦金屬與氧化鋯介面反應及其微觀結構

Abstract

本研究以兩種方式進行高溫鈦金屬與陶瓷材料的介面反應： (1)將純Ti與氧化鋯及Y2O3置於陶瓷坩堝中，以電阻加熱方式熔解Ti (1750℃/7-14 min); (2)以真空消耗性電極(Ti與Ti6Al4V)熔解鈦金屬，並澆鑄於陶模內，Ti金屬與氧化鋯陶瓷反應後的介面微觀結構使用SEM/EDS、XRD、EPMA及STEM/EDS分析之。 高溫鈦金屬與氧化鋯作用生成α-Ti(O)與鈦的氧化物(TiO, TiO2, Ti3O5, brookite)，其中由微小顆粒組成的板狀TiO2具方向性排列。在冷卻過程，α-Ti(O)的固溶體可轉變成序化(order)結構的Ti3O次氧化鈦(titanium sub-oxide)和層狀的Ti2ZrO會從α-Ti(Zr, O)固溶體以{110}Ti2ZrO//{100}α-Ti和{111}Ti2ZrO//{011}α-Ti方向關係析出。在陶瓷側，氧化鋯被還原成缺氧氧化鋯並釋出氧氣，部份的氧溶入鈦中形成為α-Ti(O)，其餘部分則以氣泡方式存在鈦晶界上。球狀或板狀α-Zr(O)會從陶瓷側的缺氧氧化鋯(ZrO2-X)析出，其中板狀α-Zr(O)具有{ }雙晶平面，並致使缺氧氧化鋯(ZrO2-y)的O/Zr比值增加至約2 : 1。在反應過程中氧化釔安定劑會隨同氧化鋯溶入鈦金屬中，且以缺氧氧化釔方式存在鈦金屬。 以真空離心鑄造將熔融Ti或Ti-6Al-4V澆鑄於陶模時，由於離心力所致，金屬液會滲透至陶模的內部，含SiO2黏結劑的ZrO2陶模與金屬液反應後轉變成ZrO2-x，金屬側則形成固溶氧的α-Ti(O)，在冷卻過程，α-Ti(O)序化(order)為Ti3O次氧化鈦(titanium sub-oxide)。氧化鋯陶模中的SiO2黏結劑會與金屬液反應生成Ti5Si3。 CP-Ti與Y2O3的介面反應並不顯著，緻密的Y2O3平板與Ti反應後，能維持平整的介面，Ti能側固溶微量氧元素和釔元素，並無其他化合物或氧化物生成，亦無氣相生成物。

Interfacial reactions between titanium and ceramics were carried out by two methods: (i) dense zirconia or yttria plates were immersed in titanium molten in a resistant furnace at 1750□C in Ar; (ii) titanium electrodes (titanium and Ti6Al4V alloy) were molten by the consumable electrode vacuum arc melting process and then the melt was cast into zirconia mold with silica binder. The interfaces between zirconia and titanium were investigated by the XRD, EPMA, SEM, and analytical TEM. □-Ti(O, Zr) and titanium oxides could form due to the dissolution of zirconia into titanium during the reaction. The lath plates of TiO2, consisting of fine crystallites, could form in the chemical reaction layer, where some metastble phases of titanium oxides, such as brookite and Ti3O5, and an ordered titanium sub-oxide (Ti3O) were also found. During cooling, the lamellae of Ti2ZrO precipitated in α-Ti with the orientation relationship of { }Ti2ZrO // {100}□-Ti and < >□Ti2ZrO // <011>□□-Ti. In the ceramic side, ZrO2 was transformed into the oxygen deficient zirconia (ZrO2-x) with the O/Zr ratio as low as 1.53 and resulted in the evolution of oxygen. Part of oxygen accumulated at the grain boundaries of titanium, the remaining being dissolved in titanium as α-Ti(O). However, both twinned □-Zr(O)□and spherical □-Zr(O) were excluded from ZrO2-x, giving rise to the formation of fine crystalline ZrO2-x with high ratio of O/Zr (□ 1.9) during cooling. In consumable electrode vacuum arc melting, interfacial reactions between titanium alloys (Ti and Ti6Al4V) and ZrO2 mold with silica binder proceeded with the penetration of titanium melt into interconnected pores by the assistance of capillary and centrifugal forces. A titanium silicide Ti5Si3 formed in the metallic side due to the reaction of titanium and silica binder. Titanium could leach oxygen to form the α-Ti(O) solid solution, which subsequently transformed into the ordered structures of TiyO (y□2) during cooling. In contrast, only thermal dissolution took place between yttria with titanium without the formation of new compound or gaseous phase. The interface of yttria and titanium retained smooth after reaction.