本篇論文以IF鋼進行低週疲勞試驗，固定應變振幅0.3%，循環週期數為3000、6000及13000週期進行低週疲勞試驗，以SEM之BEI/ECCI模式觀察試棒表面與內部之差排組織。
循環週期數為3000週期的試棒，表面上僅有少數晶粒形成持續滑移帶，此條件下內部的差排組織以差排團與差排牆為主，而表面的差排組織已經有差排胞形成，同時也有觀察到差排胞沿著其偏好方向排列的情形；當循環週數增加至6000週期時表面有少數裂縫形成，此時內部差排組織仍以差排團與差排牆為主，但已有少數錯位差排胞形成，而表面的差排組織則以差排胞較常見。
循環週期數再增加至13000週期時，試棒表面已有許多裂縫形成，包括50μm、100μm甚至是更長的裂縫，裂縫尖端的差排組織都形成尺寸小於2μm的錯位差排胞，表示這些裂縫都會繼續成長；而表面裂縫如果是由持續滑移帶形成的，晶粒內部可以觀察到沿著偏好方向排列的差排胞，而裂縫附近的差排結構為錯位差排胞。
觀察循環週期數為6000與13000週期的試棒，裂縫由表面成長至內部的裂縫，尖端的差排組織都是錯位差排胞，表示裂縫要形成時差排組織要演化成錯位差排胞後才有機會產生。

The IF steel was cycled at strain amplitude of εmax = 0.3% and the samples were cycled at 3000、6000 and 13000 for observation of surface crack, respectively. The microstructure of the surface and interior of IF steel were examined by the SEM under BEI/ECCI mode.
At 3000 cycles, we can find that many persistent slip bands (PSBs) form in grains, but it’s not easy to find cracks. The main microstructures in the interior are dislocation loop patches and dislocation walls. The microstructures at the surface are dislocation cells, and we find the dislocation cells arrange along their prefer orientation in some grains.
At 6000 cycles, there are many cracks on the surface, but the depth of cracks may be less than 10μm. The mainly microstructures in the interior and on the surface are almost the same as those at 3000 cycles, but very few dislocation cells can be observed in the interior.
When the fatigue cycles increase to 13000 cycles, there are many long cracks on the surface. The microstructure of crack tips are misorientation cells and the size of misorientation cells are less than 2μm. It means that the length of cracks will develop if the fatigue cycles increase.
As the result of the observation of surface cracks longer than 50 um in samples at 6000 and 13000 cycles, the microstructure of crack tips consists of misorientation cells which imply a propagating crack.

論文摘要…………………………………………………………….…..I
總目錄………… ..................................................................................... IV
圖目錄…….............................................................................................. VI
第一章 前言 1
1-1背景 1
1-2研究動機與目的 2
第二章 文獻回顧 4
2.1 F.C.C.材料 4
2-1.1 裂縫起始 4
2-1.2 差排結構 6
2-1.3 裂痕尖端的差排結構 6
2.2 B.C.C.材料 7
2-2.1 裂痕起始與成長 7
2-2.2 裂痕尖端的差排結構 8
2-2.3 IF鋼的差排組織 9
2-3 Gemetrically and Incidental Boundary 10
第三章 實驗方法 12
3-1 低週疲勞試棒製作 12
3-2 材料晶粒大小觀察 12
3-3 低週疲勞實驗 13
3-4試片製作 14
第四章 結果與討論 16
4-1 表面裂縫觀察 16
4-1.1 εmax = 0.3%，3000 cycles 16
4-1.2 εmax = 0.3%，6000 cycles 17
4-1.3 εmax = 0.3%，13000 cycles 18
4-2 縱切面之裂縫觀察 21
4-2.1 εmax = 0.3%，6000 cycles 21
4-2.2 εmax = 0.3%，13000 cycles 22
第五章 結論 23
第六章 參考文獻 25
圖……… 30

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