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標題: | 高熵/中熵合金退火與變形之缺陷顯微結構演變 Microstructural Evolution of High/Medium-entropy Alloys during Annealing and Deformation |
作者: | 邱柏翰 Po-Han Chiu |
指導教授: | 楊哲人 Jer-Ren Yang |
關鍵字: | 高熵合金,中熵合金,退火雙晶,機械雙晶,方位關係,背向電子繞射分析,掃描式電子顯微鏡,穿透式電子顯微鏡, High Entropy Alloys,Medium Entropy Alloys,Annealing Twin,Mechanical Twin,Orientation relationship,Electron Backscatter Diffraction (EBSD),Scanning Electron Microscope (SEM),Transmission Electron Microscope (TEM), |
出版年 : | 2022 |
學位: | 博士 |
摘要: | FCC系列之高熵/中熵合金因有其獨特之雙晶組織,在低溫及高應變速率發揮其獨特之性質。本實驗利用CrMnFeCoNi 高熵合金,經過滾軋後持溫700℃退火1至30分鐘,觀察再結晶與晶粒成長之現象。經由OIM軟體雙晶定量與密度分析,在再結晶初期,會因為快速之再結晶導致雙晶比例下降,此現象原因為再結晶初期,大量細小再結晶晶粒快速增生所致。此外,雙晶密度在退火過程持續增加至再結晶完成。透過比較CrMnFeCoNi 高熵合金滾軋退火800℃持溫1小時,雖然雙晶密度無顯著增加,但平均每個晶粒所含有之退火雙晶數增加許多。代表退火雙晶仍會在晶粒成長階段繼續發展。CrCoNiSi0.3在高溫1000℃持溫1小時退火後,單一晶粒可發展出4組不同方位之退火雙晶。利用軟體分析說明此四組退火雙晶與母相之雙晶方位關係。文中也透過極圖詳細說明退火雙晶在光學顯微鏡與電子顯微鏡形貌之成因。另外,也比較相同熱機處理之CrMnFeCoNi 高熵合金、CrFeCoNi 中熵合金、CrCoNi 中熵合金之雙晶密度與晶粒組織。在此次實驗中由於CrCoNi 中熵合金擁有最低之疊差能(18±4 mJ·m^2),CrCoNi中熵合金在雙晶密度以及雙晶比例皆比其他高中熵合金高上許多。最後透過機械測試探討機械雙晶與退火雙晶在拉伸過程之發展。在CrFeCoNi中熵合金之間斷拉伸實驗中,退火雙晶會在拉伸過程因為與母相晶粒失去雙晶關係,而提升高角度晶界之比例。除此之外,機械雙晶之真實臨界應力約為733MPa。最後,CrFeCoNi中熵合金在室溫下即便在真實應變量為 30%,僅能在單一變形晶粒觀察到一組變形雙晶的形成,推測是因為應力不足所致。 The FCC series of High/Medium-entropy alloys have a unique twin structure and exhibit unique properties at low temperatures and high strain rates. CrMnFeCoNi high-entropy alloy (HAE) is heating at 700 ° C for 1 to 30 minutes after rolling. The phenomenon of recrystallization and grain growth can be observed. According to the quantitative and density analysis of the annealing twin by OIM software, the rapid recrystallization in the early stage of recrystallization leads to the decrease in the annealing twin fraction, which is caused by the rapid growth of a large number of small recrystallized grains in the early stage of recrystallization. In addition, the twin density continues to increase during the annealing process until the recrystallization completed. In addition, by comparing the CrMnFeCoNi HEA rolled and heating at 800°C for 1 hour. Although the density of annealing twins did not increase significantly, the average number of annealing twins per grain increased a lot. This means that the annealing twins would continue to develop in the grain growth stage. CrCoNiSi0.3 can develop 4 variants of annealing twins in a single grain after annealing at high temperature of 1000°C. OIM software analysis is used to illustrate the orientation of the annealing twin in relation to the parent phase. Detailed explanation of the causes of annealing morphology in optical microscopy and electron microscopy. The density and grain structure of the annealing twin of CrMnFeCoNi HEA, CrFeCoNi MEA, and CrCoNi MEA are compared with the same thermal-mechanical treatment. In this experiment, the CrCoNi alloy had the lowest stacking energy (18±4 mJ·m^2), and the twin density and twin fraction of CrCoNi alloy was much higher than other. Finally, the development of mechanical twin and annealing twin is discussed through mechanical test in tensile. In the interrupted tensile test, CrFeCoNi MEA annealing twins were found to transformed to high angle grain boundaries progressively. Due to CrFeCoNi MEA annealing twins loss of twin relationship with the parent phase during the tensile process. Furthermore, the stress of mechanical twin is about 733 MPa, and the formation of a single variant of deformation twin at room temperature due to insufficient stress. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/91952 |
DOI: | 10.6342/NTU202203226 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 材料科學與工程學系 |
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