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系統識別號 U0026-1908202021142300
論文名稱(中文) 以修正後細胞自動機方法模擬電子束熔融金屬積層製造之微觀凝固過程
論文名稱(英文) A Modified Cellular Automaton Model for the Simulation of Micro-Solidification Process of Electron Beam Additive Manufacturing Process
校院名稱 成功大學
系所名稱(中) 工程科學系
系所名稱(英) Department of Engineering Science
學年度 108
學期 2
出版年 109
研究生(中文) 武易璋
研究生(英文) I-Chang Wu
學號 N96074405
學位類別 碩士
語文別 中文
論文頁數 122頁
口試委員 指導教授-趙隆山
口試委員-彭勳章
口試委員-張建宏
中文關鍵字 Ti-6Al-4V  電子束熔融  積層製造  MCA法 
英文關鍵字 Ti-6Al-4V  Electron Beam Additive Manufacturing  Modified Cellular Automaton Method 
學科別分類
中文摘要 電子束熔融(EBM)為金屬積層製造成型技術之一,而成品之機械性質多與成型時的溫度場與濃度場所產生之晶相有所關聯,因此對材料之凝固微結構進行數值模擬,可預測成品的凝固組織變化,有助於改善材料品質。本研究選擇修正後細胞自動機法(Modified Cellular Automaton Model, MCA method),以巨觀熱傳為基礎,結合微觀的成核、成長與溶質擴散,建立一個可同時計算巨、微觀尺度的二維模型;潛熱計算方面,將模型分為熔化區與凝固區,分別使用等效比熱法(effective specific heat method)與溫度回復法(temperature recovery method)來計算潛熱的釋放。本研究使用鈦合金(Ti-6Al-4V)作為研究材料,利用Fortran自行撰寫程式來分析電子束熔融金屬積層製造中的溫度場、濃度場以及微結構變化。本研究分為三個階段,第一階段中模擬鈦合金自由枝狀晶的形態,並模擬鋁銅合金與文獻作比對,以測試模型的合理性。最後嘗試改變濃度過冷度中的相關參數,來探討相關參數對晶粒成長形態的影響;第二階段則模擬鈦合金在方向性凝固中的晶粒形態,並模擬鋁銅合金之方向性凝固與文獻作比對,再次確認程式的準確性;第三階段中,將電子束熔融之移動路徑與邊界條件套入模型中,並加入鋪粉疊層製程,確保層與層之間是否順利接合,並且觀察晶粒尺寸於不同位置與不同層之間的變化。
由研究結果發現鈦合金由於溶質分布係數較大、液相線斜率較小,此二者使得凝固時液固介面保持相對穩定,而不利晶枝的產生,讓晶粒呈現四方型狀態,並沿液相線邊緣成核、生長。在電子束熔融金屬積層製造中,使用兩側停留方法可使層與層之間順利熔接在一起,而短暫停留造成的餘熱有機會產生額外的熔池,額外熔池之情形則取決於該次熱源掃描所捕獲的人工液固共存區多寡。濃度場中則可發現由於表層因凝固而將出多餘的溶質釋放至熔池中,而達到類似區域熔煉(zone melting)的金屬純化(purifying)的作用。積層製造中晶粒大小由左至右、由下至上,其尺寸逐漸縮小,與液相線移動方向方向相同,而在不同疊層中,較新的疊層之晶粒尺寸會普遍大於舊疊層。
英文摘要 Electron beam melting (EBM) is one of the metal additive manufacturing processes. The mechanical properties of the final product are related to the temperature field and the microstructure produced in the concentration field during the manufacturing process. In order to analyze the heat/mass transfer problem, modified cellular automaton model is adopted in this study. This theory combines micro-models of nucleation, growth and solute diffusion with the macro-models of heat transfer to establish a two-dimensional macro-micro model. The absorption and release of latent heat is computed respectively by effective specific heat method and temperature recovery method. Based on those theories, the heat/concentration transfer problem is analyzed by self-writing numerical code in FORTRAN. The process of this study divided into three stages: first stage, simulate the morphology of a free dendrite in the melt and discuss the effect of the parameters in solutal undercooling; the second stage, simulate the morphologies of directional solidification and discuss the effect of the temperature field and concentration field; the third stage, simulate the morphology of additive manufacturing process ,make sure the adjacent layer can be welded together calculate the grain size obtained from the previous stage and discuss the trend between different positions and different layers. From the results, it is found that titanium alloys have a large partition coefficient and a small liquidus slope. These two factors make the solid/liquid interface stable relatively which is harmful to the branch growing during solidification, so that the morphology of a free dendrite of titanium alloy demonstrates as a square. The small liquidus slope causes titanium alloy would nucleate and grow along the edge of the solid/liquid interface. In the process of electron beam additive manufacturing process, the heat source will stay on left side and right side to make the adjacent layer can be welded together. In the once heat source scan, the direction in which the grains gradually become smaller is the same as the direction in which the solidification line moves. In the different layer, the grains of the newer layer are generally larger than that of the older one.
論文目次 摘要 II
ABSTRACT IV
致謝 XIII
目錄 XIV
表目錄 XVII
圖目錄 XVIII
符號說明 XXI
第一章 緒論 1
1-1 實驗背景與動機 1
1-2 凝固過程微觀模擬發展與本文研究方法 1
1-2-1 凝固過程微觀模擬發展過程 1
1-2-2 本文研究方法與目的 4
1-3 電子束熔融技術 4
1-3-1 電子束熔融技術原理 5
1-3-2 電子束熔融技術問題及改善 5
第二章 凝固理論模型 11
2-1 物理模型 11
2-2 基本假設 12
2-2-1 巨觀模式假設 12
2-2-2 微觀模式假設 12
2-3 成核(Nucleation)模式 13
2-4 枝狀晶成長(Growth)模式 14
2-4-1 枝狀晶生長原理 14
2-4-2 枝狀晶頂端成長動力學 15
2-4-3 成長方向 17
2-5 統御方程式(Governing Equation) 19
2-5-1 溫度場 19
2-5-2 濃度場 20
2-6 邊界條件(Boundary Condition) 21
2-6-1 溫度場 21
2-6-2 濃度場 21
第三章 數值方法 30
3-1 網格配置與網格參數設定 30
3-2 成核模式 30
3-3 枝狀晶成長模式 31
3-3-1 過冷度計算 31
3-3-2 表面曲率(Interface Curvature)計算 32
3-3-3 成長長度計算 32
3-3-4 固態分率計算 33
3-4 巨觀溫度場 33
3-4-1 溫度場數值方程式 33
3-4-2 溫度場邊界條件 35
3-4-3 移動熱源處理 36
3-5 微觀濃度場 36
3-5-1 液相區濃度場 36
3-5-2 固相區濃度場 36
3-5-3 濃度場邊界處理 37
3-6 時間步伐計算 38
3-6-1 巨觀時間 38
3-6-2 微觀時間 38
3-7 流程圖 39
第四章 結果與討論 44
4-1 液固介面之枝狀晶頂端成長參數猜測 45
4-2 自由枝狀晶形態之模擬 45
4-2-1 形態模擬 45
4-2-2 不同成長角度模擬 47
4-2-3 濃度過冷度不同參數之影響 47
4-3 方向性凝固模擬 48
4-3-1 形態模擬 48
4-3-2 濃度與溫度分布對凝固影響 48
4-4 積層製造模擬 49
4-4-1 兩側無停留之積層製造模擬 49
4-4-2 兩側停留之積層製造模擬 51
4-5 晶粒尺寸比較 52
4-5-1 橫截面晶粒尺寸 52
4-5-2 縱截面晶粒尺寸 53
第五章 結論 115
5-1 未來展望 117
參考文獻 118
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