近年來，俗稱3D列印的積層製造技術日益成熟且普及，其具有客製化與複雜三維度結構製造的優勢，被認為是第三次工業革命的關鍵技術，也因此受到航太與生物醫學領域越來越多的關注，其製造方式有別於傳統的「減法式製造」而是採用「加法式製造」，並結合電腦輔助設計軟體繪製3D模型，再經由切層軟體將工件的3D模型解構為一層一層的幾何形狀之2.5D平面，以層層堆疊或燒熔的方式，將原材料製造成立體物品，此方法降低了加工過程中以切削或刮除所帶來的額外加工與材料成本，而能夠有效減少材料的浪費，並提高材料利用率，而由於Ti-6Al-4V合金具有優異的比強度、抗腐蝕性及良好的生物相容性，已被廣泛應用於航太與生醫領域，作為渦輪葉片或金屬植入物來使用，因此Ti-6Al-4V合金在金屬積層製造技術中扮演一重要的角色。
典型的金屬粉末熔融積層製造技術中，以加熱源可區分為選擇性雷射製造技術及電子束積層熔融製造技術，選擇性雷射製造技術為一相對成熟的製程，不僅選擇材料的彈性較大，製造精密度也較後者來的高，但具有真空環境與預熱機制的電子束積層熔融製造技術，在腔體潔淨度與工件殘留應力的控制上更具優勢。雖然積層製造技術帶來了傳統製造工法沒有辦法達到的高度，然而多樣的製程參數與條件，使其在成品工件的微結構與機械性質上更加困難，且過去多以經驗或直覺的製程參數設置，造成單一合金系統的製程開發需要大量的時間及成本。因此，需要了解特定製程條件與不同合金系統之微結構與機械性質關係，以加速商業化與產業應用。
在本研究中，利用電弧熔融法製備如金屬積層製造之快速凝固Ti-6Al-4V合金，並以紅外線溫度計量測合金溫度變化歷程，來計算合金之冷卻速率，並結合熱力學計算方法來探討快速凝固中的相變化行為，同時也透過微結構與機械性質之分析，觀察冷卻速率與兩者之關係。其實驗結果可成功描述積層製造中極快之凝固速率，且針狀α^'厚度隨著冷卻速率升高而減小，同時伴隨著硬度的提高，而通過計算結果能夠合理的解釋Ti-6Al-4V合金的相變化過程。除了前端製程之研究外，本研究同時也將電子束積層熔融製程後的Ti-6Al-4V合金進行後續的熱處理，在熱處理溫度750-950 °C下退火一小時，接著以水冷淬火與空冷方式冷卻，進而探討熱處理條件對其微結構與機械性質之影響，擺脫過去僅透過熱等靜壓方式進行後續處理的熱處理發展限制。從實驗結果發現其prior β晶粒尺寸將不因熱處理條件不同而改變，且β相面積分率、片狀α/α'與棒狀β之厚度皆隨著熱處理溫度而成長，並有導致其硬度的降低，然而當熱處理溫度超過800 °C以上，施以淬火與空冷時，將分別形成α'與針狀α/α'，進而造成其硬度的提高。

The additive manufacturing (AM) technology used in metals processing involve rapid solidification and rapid cooling at small melting pool dimensions as well as multiple reheating and cooling cycles. A method for characterization of the microstructure formation in rapidly solidified alloys was developed and applied for Ti-6Al-4V alloy. Otherwise, the relation between microstructure and mechanical properties has been mainly limited to the as-fabricated condition for electron beam melting (EBM) of metal powder bed fusion additive manufacturing technology. In this work, we measured the relationship of cooling rate, microstructure and hardness of rapid solidified Ti-6Al-4V alloys. Also the influence of heat treatment on microstructure and mechanical property of Ti-6Al-4V alloys fabricated by the EBM technology. The microstructures of rapid solidified Ti-6Al-4V alloys consist of acicular α/α'. The thickness of acicular α/α' decrease with increasing hardness and cooling rate. Based on thermodynamic calculations the observed microstructure can be explained using the CALPHAD approach tacking into account the non-equilibrium condition. The effect of heat treatment on microstructure and mechanical property is discussed in terms of α and β phases. The results show that α lath and β rod grow with increasing annealing temperature which cause in a decrease in hardness. However, α' and acicular α/α' will form respectively when the annealing temperature exceeds 800 °C and cooled by water-quenching and air-cooling which result in an increase in hardness.

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