雷射熱處理可在維持材料本身強度及韌性前提下，改變表層組織結構，以改善表層之硬度、耐磨耗性、耐疲勞性等，使零組件在嚴苛的工作環境下或機構作動下承受負載及磨耗時，延長其有效壽命。
工程應用上，因雷射源光斑幾何尺寸受限，若零組件表面需大面積硬化，則須規劃多道掃掠路徑，保證硬化層硬度、深度達要求的同時，硬化品質也需均勻，反之隨機構作動時間拉長，硬度不均導致表面磨耗不一，亦或是內部生成金相組織不同，皆會造成作動件的尺寸精度產生誤差。
本研究旨在探討二極體雷射以雙道掃掠路徑方式對中碳合金鋼AISI 4140進行表面熱處理，以控制溫度方式搭配不同雷射參數下，分析回火效應對熱影響重疊區之硬化層深硬度、金相之影響，並利用調控雷射加工參數，以降低回火效應造成之硬度下降影響，得到一均勻硬化之表面。結果顯示在1100℃下，雙道路徑距離為3mm、進給速度為300mm/min時，兩硬化層平均硬度分別達HV627、HV736，且受回火區域硬度依然達HV505。

Laser heat treatment changes microstructure of surface to improve hardness, wear resistance, fatigue strength when the bulk material retains high strength and toughness so that mechanical components extend its operating life which works in harsh conditions or being under heavy load and wear.
As the laser beam has a limited spot dimension, when the workpiece requires a large area of hardening, multiple tracks have to be applied. In addition to ensuring the requirements of hardness and depth of hardened zone, the quality should be uniform. On the contrary, with a long time for operating, both uneven wear by non-uniform hardness distribution and different metallurgical structure will cause the dimensional error.
Hardness decreased by back tempering is one of the most critical problems in laser heat treatment of large surfaces. In this paper, a diode laser with different process parameters was used to harden the surface of AISI 4140 by double track. The effect of hardness profile and microstructure of the hardened zone by back tempering was analyzed. And carefully controlling the process parameters to minimize the drawbacks of hardness decreased by tempering. The average hardness of two hardened zones was HV627, HV736, and the tempering area still reached HV505 by using 1100℃control temperature with a feed rate of 300 mm/min and a distance between the double track of 3mm.

誌謝 i
摘要 ii
Abstract iii
目錄 iv
圖次 vi
表次 viii
符號表 ix
第一章 緒論 1
1.1前言 1
1.2文獻回顧 1
1.3研究方法 4
1.4論文架構 4
第二章 雷射熱處理及雙道回火效應 6
2.1雷射熱處理 6
2.1.1雷射加工介紹 6
2.1.2表面硬化技術比較 8
2.1.3雷射加工參數 11
2.2雙道回火效應 14
第三章 實驗方法 16
3.1實驗流程 16
3.2實驗試片 17
3.2雷射加工參數試驗 18
3.3雷射雙道掃掠路徑 19
3.4微硬度分析 20
3.5金相分析 22
第四章 實驗結果與討論 24
4.1雷射單道直線路徑微硬度分析 24
4.2雷射雙道直線路徑微硬度分析 30
4.3雷射雙道直線路徑金相顯微組織分析 43
第五章 結論 49
參考文獻 50

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