奈米雙晶銅箔機械性質與氧化動力學之研究;Investigation of the Mechanical Properties and Oxidation Kinetics of Nanotwinned Copper Foils

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Title:	奈米雙晶銅箔機械性質與氧化動力學之研究;Investigation of the Mechanical Properties and Oxidation Kinetics of Nanotwinned Copper Foils
Authors:	張睿勝;Jui-Sheng, Chang
Contributors:	化學工程與材料工程學系
Keywords:	奈米雙晶銅;拉身試驗;非線性彈性;破裂行為;銅氧化;Nanotwinned Copper;Tensile test;Nonlinear elastic;Fracture Behavior;Copper oxidation
Date:	2025-08-25
Issue Date:	2025-10-17 11:39:21 (UTC+8)
Publisher:	國立中央大學
Abstract:	奈米雙晶銅因具有高密度的共格雙晶界 (CTB)，使其具有高機械強度、高熱穩定性、抗電遷移能力和抗氧化能力等諸多優點，成為應用於電子封裝與鋰電池負極集電體之理想材料，有助於提升產品整體可靠性。本研究的第一部分針對厚度為 60、20、10 與 5 μm 之奈米雙晶銅箔進行單軸拉伸試驗，結果顯示，隨厚度減薄，銅箔之降伏強度與抗拉強度顯著上升 (60 μm與5 μm銅箔最高可分別達 505 MPa 與 965 MPa)，但延展性明顯下降，5 μm 銅箔之斷裂伸長率僅約 4.75%，遠低於60 μm之伸長率19.84%。顯微結構分析揭示：厚箔中晶粒尺寸較大，Type I 與 Type II 差排之滑移方向與雙晶界相交，滑移受阻導致差排堆積於雙晶界面，產生強化效應並促進去雙晶 (de-twinning)；而 Type III 差排則平行於雙晶界，滑移距離增加，增加銅箔延展性。進一步分析破斷區域微結構變化，發現銅箔的塑性變型過程中同時伴隨去雙晶 (de-twinning)與非共格雙晶界 (ITB)遷移，而在頸縮區域甚至觀察到柱狀晶粒旋轉等現象。此外，在應力–應變曲線中可觀察到彈性區的非線性行為。為描述此現象，本研究採用 Ramberg–Osgood模型進行擬合，並描述非線性彈性行為的偏離程度。第二部分討論在高溫氧化行為方面，分別選用三種具有代表性的銅微結構進行比較：奈米雙晶 (NT)、超細晶 (UFG) 與粗晶(Normal)。將樣品置於300 °C條件下進行等時氧化實驗，並藉由FIB橫截面與XPS分析觀察氧化層厚度與化學態變化。結果顯示，三種結構皆呈現線性氧化動力學，但氧化速率依序為 Normal > UFG > NT，其中NT銅顯現出最優異的抗氧化能力。藉由表面能與懸鍵數之分析指出：nt-Cu 表面主要為 (111) 晶面，具最低懸鍵數與表面能，氧氣吸附與活化受限，反應速率較低；Normal-Cu 表面為高懸鍵數之 (110) 晶面，因此氧化速率最快；UFG-Cu 則因高晶界密度初期加速氧氣擴散，但因高溫氧化過程中晶粒成長，其速率逐漸趨緩。本研究更進一步推導線性氧化速率常數與表面懸鍵數及活化能之關係式，建立表面微結構與氧化動力學的模型連結。 ;Nanotwinned copper (nt-Cu), owing to its high density of coherent twin boundaries (CTBs), exhibits superior mechanical strength, thermal stability, resistance to electromigration, and oxidation resistance. These advantages make it an ideal material for applications in electronic packaging and as current collectors in lithium-ion battery anodes, thereby enhancing overall device reliability. In the first part of this study, uniaxial tensile tests were performed on nt-Cu foils with thicknesses of 60, 20, 10, and 5 μm. The results showed that as the thickness decreased, both yield strength and ultimate tensile strength increased significantly (with the 60 μm and 5 μm foils reaching up to 505 MPa and 965 MPa, respectively). However, ductility decreased markedly, with the elongation to fracture of the 5 μm foil reduced to approximately 4.75%, compared to 19.84% for the 60 μm foil. Microstructural analysis revealed that in thicker foils with larger grain sizes, Type I and Type II dislocations intersected with twin boundaries, resulting in dislocation pile-up at the CTBs, which enhanced strengthening and promoted de-twinning. In contrast, Type III dislocations—sliding parallel to the twin boundaries—exhibited longer glide distances, thereby contributing to improved ductility. Further analysis of the fractured regions revealed that plastic deformation was accompanied by de-twinning, migration of incoherent twin boundaries (ITBs), and even rotation of columnar grains in the necking regions. Additionally, the stress–strain curves exhibited nonlinear behavior in the elastic regime. To capture this deviation from linear elasticity, the Ramberg–Osgood model was employed to describe the extent of nonlinear elastic deformation. The second part of this study focused on the high-temperature oxidation behavior of three representative copper microstructures: nanotwinned (NT), ultrafine-grained (UFG), and coarse-grained (Normal) Cu. Isothermal oxidation was performed at 300 °C, and the oxide layer thickness and chemical states were analyzed using FIB cross-sections and XPS. Results showed that all three structures followed linear oxidation kinetics, with the oxidation rate ranking as Normal > UFG > NT, confirming that NT-Cu exhibited the best oxidation resistance. Analysis of surface energy and dangling bonds revealed that NT-Cu predominantly exposes (111) planes, which possess the lowest number of dangling bonds and surface energy, thereby limiting oxygen adsorption and activation and reducing oxidation rates. In contrast, Normal-Cu surfaces were mainly (110)-oriented, with the highest density of dangling bonds and surface energy, resulting in the fastest oxidation. UFG-Cu initially showed rapid oxidation due to its high grain boundary density, which facilitated oxygen diffusion, but its oxidation rate decreased as grains coarsened during high-temperature exposure. Furthermore, a kinetic model was established by deriving the relationship between the linear oxidation rate constant, the number of dangling bonds, and activation energy, providing a quantitative link between surface microstructure and oxidation behavior.
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