臺灣博碩士論文加值系統

雷射製程與傳統的熱處理及加工製程不同，因雷射高能量密度以及局部小範圍加熱的特性，再加上多元的雷射製程參數，使被處理工件產生複雜的熱歷程。不同的熱歷程會經歷不同的相變態過程，而得到不一樣的相組織，相組織將決定材料的機械性質。本研究可分為兩個部分。首先，以有限元素方法為基礎，針對雷射表面改質製程，分析雷射掃描Ti-6Al-4V合金工件的溫度場。第二，以相圖以及半經驗公式為基礎，建立一套數學方法，根據熱場分析所提供的溫度函數進行相組織的計算。
溫度場的結果提供了熔池的幾何，並可用來預測熱影響區的範圍及尺寸。相組織的模擬則提供了製程中，Ti-6Al-4V合金各相體積分率的變化歷程，以及最終的相組成。發現熱影響區中各元素的麻田散體相體積分率皆為80 %左右，且β相相體積分率從製程前的30 %降為18.9 %。根據相組成進一步計算微硬度值後，發現計算值與實驗結果吻合，證實了相組織模擬的準確性與可靠性，未來可以此模型為基礎，應用於選擇性雷射熔融製程的相組織計算。

Laser surface modification is a technique that treats the materials locally to change the material properties. Complex thermal histories are induced at different sites during the laser surface modification process because of the various laser parameters and scanning paths. Diverse thermal histories would lead to different phase transformations that finally decide the microstructure and material properties.
In this study, a finite element model and a mathematical model were built and validated to provide reliable temperatures as a function of time and location and simulate the phase transformations respectively. The hardness was evaluated by the rules of mixture on the basis of the simulated phase compositions and validated by experimental results. Eventually, the simulations were conducted at different laser scanning speeds. The faster laser scanning speed leads to a smaller heat-affected zone but a larger hardness value of the heat-affected zone.

摘要 I
Extended Abstract II
誌謝 VIII
目錄 X
表目錄 XIII
圖目錄 XIV
第一章 前言 1
1.1 研究背景 1
1.2 文獻回顧 2
1.2.1 雷射輔助製程 2
1.2.2 雷射表面改質製程與數值模擬 4
1.2.3 鈦合金分類 5
1.2.4 Ti-6Al-4V合金 9
1.2.5 鈦合金的組織與機械性質 9
1.2.6 相變態數值模擬 11
1.2.7 Ti-6Al-4V合金相變態 12
1.3 研究目的 13
第二章 數值方法與理論基礎 16
2.1 雷射熱源 16
2.2 熱傳模擬分析 17
2.3 相變態計算 19
2.3.1 擴散相變 20
2.3.2 無擴散相變 21
2.3.3 Ti-6Al-4V合金相變計算流程 22
2.4 硬度值計算 26
第三章 研究方法與步驟 30
3.1 模擬流程 30
3.2 熱場模擬系統 30
3.2.1 模型建立 30
3.2.2 模擬假設 32
3.2.3 模型驗證 32
3.3 相變態模擬系統 33
3.3.1 模型建立 33
3.3.2 模擬假設 34
第四章 結果與討論 40
4.1 三維溫度場模擬結果與驗證 40
4.2 雷射表面改質製程下Ti-6Al-4V合金的相組織模擬 42
4.2.1 相組織體積分率的變化歷程 42
4.2.2 製程結束後相組織的分佈情形 44
4.3 雷射表面改質製程對Ti-6Al-4V合金相組織及硬度的影響 45
4.4 不同雷射掃描速度對熱影響區尺寸及相組織的影響 46
第五章 結論 65
參考文獻 66

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