利用超高解析電鏡分析單晶3C-碳化矽與SA-Tyrannohex全纖維碳化矽複合材料在高溫矽離子輻照下之缺陷

Ultra-high Resolution TEM Analysis of Defect in Si Ion-irradiated Single Crystal 3C-SiC and SA-Tyrannohex SiC Fiber-bonded Composite at High Temperatures

何雋禹(Chun-Yu Ho)

指導教授 ： 開執中

國立清華大學/原子科學院/核子工程與科學研究所/碩士(2013年)

摘要

碳化矽基材陶瓷近二、三十年來被認為是具有潛力與吸引力的核能結構材料。核能結構材料需承受高溫、高應力、高輻射劑量。目前碳化矽/碳化矽複合材料被選定為新核能材料，應用於高溫氣冷式反應器、核融合反應器、和用以取代輕水式反應器部分合金材料。
本實驗之主要目的為利用高解析電子顯微鏡，分析單晶碳化矽與全纖維碳化矽複合材料在高溫輻照環境之下，所造成之缺陷的顯微結構變化。利用清華大學加速器館之高能離子加速器以7 MeV Si3+離子輻照單晶3C-碳化矽和二維SA-Tyrannohex全纖維碳化矽/碳化矽複合材料，用以模擬碳化矽材料在核能反應器中所受之高溫輻射效應。輻照損傷劑量定在5和20 dpa，爐心材料於高溫氣冷式反應器中，一年所受之劑量小於2 dpa。單晶碳化矽於1000、1200和1350℃下進行實驗，碳化矽複合材料則於1000和1350℃下進行實驗。並使用掃描穿透式電子顯微鏡分析。
單晶3C-碳化矽輻照實驗中，平面缺陷在1000℃/ 5 dpa即形成，缺陷密度隨著溫度上升而下降，缺陷大小則隨溫度上升而增大。利用高解析原子影像分析，可解析輻照溫度1000℃以上所產生之平面缺陷為外置型差排環與內置型差排環，並透過球面相差修正掃描穿透式電子顯微鏡所拍攝之環型明場像，成功解析出差排環疊差的原子結構。此外，在輻照後的單晶碳化矽並無發現空孔存在，推測為因內置型插排環（空缺差排環）的疊差能低、部分空缺擴散至表面逸散、或形成之空缺（di-vacancy or tri-vacancy）太小無法以TEM觀察。
SA-Tyrannohex全纖維碳化矽複合材料輻照實驗中，於碳化矽晶粒內觀察到差排環和空孔等缺陷。此複合材料能有效抑制空孔的成長與減低空孔數量，原因為晶粒大小為300 nm左右，密度高的晶界有助於吸收空缺原子；且不像其他碳化矽複合材料輻照後，空孔會傾向形成於晶粒較大的基材處。此外，碳化矽複合材料中的氧化鋁受高溫輻照後，會形成有優選方向且大尺寸的空孔，可能影響材料的機械性質。因此，二維SA-Tyrannohex全纖維碳化矽複合材料若應用於高溫反應器，除了碳化矽受輻照的影響外，氧化鋁在材料中的含量也須考慮。

關鍵字

碳化矽 ； 穿透式電子顯微鏡 ； 輻射損傷

並列摘要

Silicon carbides (SiC) are considered as one of the promising candidates for structural and core materials used in fusion reactor and high temperature gas-cooled reactor (HTGR) due to its high thermal stability, and good resistance to irradiation and chemical attack. Single crystal 3C-SiC with less intrinsic defects was used to precisely characterize the radiation-induced defects in 3C-SiC. In addition, there are limited discussions related to radiation effect of SA-Tyrannohex fiber-bonded composite at high temperatures. Therefore, in this study, single crystal 3C-SiC thin film and SA-Tyrannohex SiC fiber-bonded composite were irradiated at 1000℃ to 1350℃ with 7MeV Si3+ ion to simulate the neutron irradiation in reactors. The microstructure of the irradiated SiC was examined by using high resolution transmission electron microscope (HRTEM) and spherical aberration corrected scanning TEM (Cs-corrected STEM).
In irradiated single crystal 3C-SiC, high resolution images showed that the planar defects were extrinsic stacking faulted loop with changing atomic sequences and intrinsic stacking faulted loop, i.e. vacancy loop. The atomic configurations were confirmed by STEM annular bright field image. However, no void has been found in single crystal 3C-SiC due to formation of vacancy loops, vacancies releasing from surface, or too small to be visible (<1 nm).
In addition, dislocation loops, voids, and edge dislocations in SA-Tyrannohex SiC fiber-bonded composite after irradiation were investigated. This SiC composite are able to suppress void growth and lower the void density after high-temperature irradiation due to its small grain size (~300 nm). Besides, larger voids (with diameter 10-40 nm) formed in alumina with preferred orientation after irradiation perhaps resulting in degradation of strength of the SA-Tyrannohex SiC fiber-bonded composite.

並列關鍵字

SiC ； TEM ； Radiation damage

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