臺灣博碩士論文加值系統

多晶銅在低週疲勞試驗下，其固定應變振幅所產生的差排組織演化，隨著疲勞循環週期的增加，差排組織逐步地由差排團，脈狀組織，持續滑移帶，差排牆，差排胞，演化至最後的錯位差排胞。但是當進行減低負荷振幅疲勞試驗，其差排組織的演化將有所改變。
本篇論文以99.99at%，晶粒大小60µm的多晶純銅，進行低週疲勞試驗，先以固定應變振幅0.4%、0.2%、0.1%，進行低週疲勞試驗至試棒斷裂(固定應變振幅0.1%，待試棒斷裂可能需要百萬循環週期以上，故進行至260000疲勞循環週期即停止)，另以固定應變振幅0.4%，進行至2500疲勞循環週期，以電子顯微鏡觀察其差排組織。
將固定應變振幅0.4%，進行至2500疲勞循環週期的試棒，減負荷至應變振幅0.2%，選擇減負荷後進行至1000、10000、30000疲勞循環週期；再同樣以固定應變振幅0.4%，進行至2500疲勞循環週期的試棒，減負荷至應變振幅0.1%，選擇減負荷後進行至1000、50000疲勞循環週期，以電子顯微鏡觀察以上試棒內部差排組織，由此可得知減低負荷振幅後，差排演化過程中的形貌。
由固定應變振幅0.4%，進行2500循環週期，減負荷至應變振幅0.2%、0.1%，進行1000循環週期，觀察到差排胞在晶界處演變為差排牆，違反舊有差排正向演化理論，證實純銅內部差排組織的確有逆演化現象；減負荷至應變振幅0.2%，進行10000循環週期，觀察到差排胞崩解為差排團；減負荷至應變振幅0.1%，進行50000循環週期，可觀察到大範圍的差排牆，部分崩解為差排團。

The dislocation structure evolution of polycrystalline copper at constant strain amplitude during low cycle fatigue develops loop patches, vein structure, persistent slip bands, dislocation walls, dislocation cells, and cells with misorientation dislocation step-by-step by increasing fatigue cycles. However, the dislocation structure evolution will change in low cycle fatigue under reduced loading amplitude.
The polycrystalline copper of 99.99 at% purity and 60µm in grain size was used in the low cycle fatigue test. First, the test is controlled at Δε/2= ±0.4%, ±0.2%, and ±0.1% strain amplitude until the specimens crack. And control the fatigue test after 2500 cycles at ±0.4% strain amplitude. Then we can observe the dislocation structure of above specimens by electron microscope.
After 2500 cycles at ±0.4% strain amplitude, change the strain amplitude from ±0.4% to ±0.2%. We chose the steps of low cycle fatigue test under reduced loading amplitude at 1000, 10000, and 30000 cycles. By the same token, change the strain amplitude from ±0.4% to ±0.2%. We chose the steps of low cycle fatigue test under reduced loading amplitude at 1000, and 50000 cycles. Then observe the dislocation structure of above specimens by electron microscope, and we can know the dislocation morphology of evolution process under reduced loading amplitude.
After 2500 cycles at ±0.4% strain amplitude, change the strain amplitude from ±0.4% to ±0.2% and from ±0.4% to ±0.1%. After 1000 cycles, the dislocation wall can be observed at grain boundary. After 10000 cycles under changed loading amplitude from ±0.4% to ±0.2%, we can observe that the dislocation cells are broken and evolve loop patches. And after 50000 cycles under changed loading amplitude from ±0.4% to ±0.1%, large area of dislocation walls and some loop patches can be observed.

目錄
壹、前言................................................1
1.1 背景................................................1
1.2 研究動機與目的....................................2
貳、理論基礎與文獻回顧..................................4
2.1 純銅的疲勞現象和差排組織............................4
2.2 疲勞裂痕的起始與成長................................7
2.3 低週疲勞............................................8
2.3.1 低週疲勞試驗......................................8
2.3.2 循環應變與循環應力應變曲線........................9
2.4 以掃瞄式電子顯微鏡背向散射電子成像觀察差排組織.....11
參、實驗方法...........................................13
3.1 材料選擇與前處理...................................13
3.2 低週疲勞試棒製作...................................13
3.3 材料晶粒大小觀察...................................14
3.4 低週疲勞實驗.......................................14
3.5 本實驗試棒參數及減負荷循環週期數取決...............14
3.6 微結構組織觀察試片製作.............................16
肆、實驗結果與討論.....................................18
4.1 固定應變振幅在0.4%、0.2%、0.1%.....................18
4.1.1 Stress responses.................................18
4.1.2 固定應變振幅0.4%、0.2%、0.1%之微結構觀察.........19
4.1.3 固定應變振幅0.4%，進行2500循環週期之微結構觀察...19
4.2 減低負荷振幅：固定應變振幅0.4%、進行2500循環週期後
，降低至應變振幅0.2%、0.1%.........................20
4.2.1 Stress responses.................................21
4.2.2 減負荷至應變振幅0.2%，進行1000循環週期之微結構
觀察.............................................22
4.2.3 減負荷至應變振幅0.1%，進行1000循環週期之微結構
觀察.............................................22
4.2.4 減負荷至應變振幅0.2%，進行10000循環週期之微結構
觀察.............................................24
4.2.5 減負荷至應變振幅0.1%，進行50000循環週期之微結構
觀察.............................................24
4.3 多晶純銅差排組織逆演化機制探討.....................25
伍、結論...............................................28
陸、參考文獻...........................................29
柒、表.................................................33
捌、圖.................................................37

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