高熵合金的概念於1995年由國立清華大學葉均蔚教授提出，這一材料研究領域的開拓引起了全球材料界的關注，高熵合金作為一個新興領域，如果能夠將高熵合金應用於日常生活中，使其像傳統商用合金一樣普及，將成為高熵合金領域的一大里程碑。在傳統工業中，以Al、Cu、Ni為主的合金是除了鋼鐵外最常見的結構材料之一，許多高熵合金的研究文獻也探討了Al、Cu、Ni等元素系統的合金性質，但是這些研究通常著重於高溫高強度的元素組合，因此，本研究選擇以這三種元素加入Sn來製作合金，以探討此較非高溫高強的合金系統的性質表現。
　　本研究欲透過了解高（中）熵合金的機械性質與腐蝕性質可以發展其應用層面的潛力，以相平衡實驗結果提供可靠的800 °C等溫橫截面圖，並利用固化分析結果確認液相線投影圖的相區與相變溫度，相圖實驗的結果也能應用於優化CompuTherm資料庫中的相圖參數。機械性質方面，測量維氏硬度和拉伸曲線，由硬度和彈性模數了解合金在受力後的變化形式；在腐蝕性質方面，合金在0.1 M HNO3和3.5 wt% NaCl的1 : 1混合溶液中測量極化曲線圖，以評估各合金在腐蝕環境中的耐腐蝕性能。
　　800 °C相平衡與相圖，Al-Cu-Ni、Al-Ni-Sn和Cu-Ni-Sn合金的相平衡結果與文獻相符，Al-Cu-Sn則無相關文獻探討，共12種合金進行相平衡，發現了FCC、Liquid單相區，FCC + BCC(β-AlCu4)、γ-Al4Cu9 + Liquid、ε-Al2Cu3+ Liquid兩相區，以及BCC(β-AlCu4) + γ-Al4Cu9 + Liquid三相區平衡，實驗相區結果與計算結果相區不同，因此繪製了修正的等溫橫截面圖。Al-Cu-Ni-Sn的9種合金中，發現Liquid + B2(AlNi) 、Liquid + AlCu_ε固液兩相，B2(AlNi) + CuSn_γ、B2(AlNi) + Ni3Sn2兩固相平衡區，以及Liquid + B2(AlNi) + CuSn_γ + Ni3Sn2四相平衡區。
　　Al-Cu-Ni的液相線投影圖中，所製作的3種合金第一析出相與計算相區相同，分別為Al3Ni、Al7Cu4Ni、Al3Ni2，但合金實際的凝固路徑與計算的結果不同。Al-Cu-Sn和Al-Ni-Sn的液相線投影圖，確認有液相不互溶區間的存在，而由Al-Ni-Sn合金的熱分析溫度，發現Liquid + Al3Ni + FCC相反應約為857 °C，高於二元邊界的L → Al + Al3Ni共晶反應溫度，640 °C，因此在靠近Al-Ni邊界處應有鞍點的存在。在Al-Cu-Ni-Sn合金中，以固化路徑進行分析，計算的相圖固化路徑比實際合金的金相觀察所呈現的凝固過程複雜許多，但4種合金都是B2(AlNi)為第一析出相，與計算結果一致。
　　合金硬度測試的結果顯示，4種Al-Cu-Ni合金硬度皆約為400 - 550　HV。而Al-Cu-Sn和Al-Ni-Sn合金中，合金由於不互溶液相凝固成不同相區，Sn相和化合物相兩種相區具有很大的硬度差異。在Cu-Ni-Sn合金中，當Ni3Sn2為第一析出相時，其硬度約為600 HV，具有耐磨損應用的可能性。而拉伸測試中，Al-Cu-Ni、Al-Cu-Sn和Al-Ni-Sn合金的彈性模數分別為214.47、35.11和75.61 GPa。而因為無法製備Cu-Ni-Sn和Al-Cu-Ni-Sn合金試片，其拉伸性質未能進行評估。
　　腐蝕性質量測中，共製作6個合金，包括4種等比例組成的三元合金合金，以及2種四元合金。結果顯示，合金的腐蝕電位範圍從-0.06186到0.80445 (V/cm2)，其中最低的是Al-40at.%Cu-20at.%Ni-20at.%Sn合金，而最高的是Al-Ni-Sn三元合金，其抗腐蝕性最佳。在觀察陽極極化曲線時，只有Al-Cu-Ni合金和Al-20at.%Cu-20at.%Ni-20at.%Sn合金出現了鈍化現象。

The concept of high-entropy alloys was proposed by Professor Yeh Jien-Wei of National Tsing Hua University in 1995, sparking global interest in the field of materials science. As an emerging area, the widespread application of high-entropy alloys in everyday life akin to traditional commercial alloys would mark a significant milestone in this field. While many studies in traditional industries focus on alloy systems primarily composed of Al, Cu, and Ni, which are among the most common structural materials apart from steel, research on high-entropy alloys often emphasizes combinations for high temperature and strength applications. Therefore, this study opts to incorporate Sn into these three elements to investigate the properties of this less extreme alloy system.

This study aims to explore the potential applications of high (medium) entropy alloys by understanding their mechanical and corrosion properties. Reliable 800°C isothermal cross-section diagrams are provided through phase equilibrium experiments, and solidification analysis confirms the phase regions and transition temperatures of the liquidus projection diagrams. The results of phase diagram experiments can also be applied to optimize the phase diagram parameters in the CompuTherm database. Regarding mechanical properties, Vickers hardness and tensile curves are measured to understand the alloy's behavior under stress. Concerning corrosion properties, polarization curves are measured in a 0.1 M HNO3 and 3.5 wt% NaCl 1:1 mixed solution to evaluate the corrosion resistance of each alloy in corrosive environments.

In the 800 °C phase equilibrium and phase diagrams, the results for Al-Cu-Ni, Al-Ni-Sn, and Cu-Ni-Sn alloys align with literature findings. However, there is no related literature on Al-Cu-Sn, thus 12 alloys are investigated for phase equilibrium, revealing various single-phase regions such as FCC and Liquid, dual-phase regions like FCC + BCC(β-AlCu4), γ-Al4Cu9 + Liquid, ε-Al2Cu3 + Liquid, and triple-phase regions such as BCC(β-AlCu4) + γ-Al4Cu9 + Liquid. Experimental phase region results differ from calculated ones, thus corrected isothermal cross-section diagrams are depicted. For the nine Al-Cu-Ni-Sn alloys, phase equilibrium analysis shows regions like Liquid + B2(AlNi), Liquid + AlCu_ε solid-liquid, B2(AlNi) + CuSn_γ, B2(AlNi) + Ni3Sn2 solid phases, and a four-phase equilibrium region.

In the liquidus projection diagram of Al-Cu-Ni, the first precipitated phases match calculated phase regions, including Al3Ni, Al7Cu4Ni, and Al3Ni2, but the actual solidification paths differ from calculations. In Al-Cu-Sn and Al-Ni-Sn liquidus projection diagrams, the presence of immiscible liquid phases is confirmed. Thermal analysis temperatures of Al-Ni-Sn alloys suggest a Liquid + Al3Ni + FCC reaction at approximately 857 °C, higher than the L → Al + Al3Ni eutectic reaction temperature of 640 °C, indicating the presence of a saddle point near the Al-Ni boundary. In Al-Cu-Ni-Sn alloys, solidification path analysis indicates more complex solidification processes than those observed in metallographic examinations, but all four alloys primarily precipitate B2(AlNi), consistent with calculations.

Hardness testing results show that the hardness of the four Al-Cu-Ni alloys ranges from approximately 400 - 550 HV. In Al-Cu-Sn and Al-Ni-Sn alloys, the hardness differs significantly between the Sn phase and compound phase due to the non-miscible liquid phase solidifying into different phase regions. In Cu-Ni-Sn alloys, when Ni3Sn2 is the first precipitated phase, its hardness is approximately 600 HV, suggesting potential for wear-resistant applications. In tensile testing, the elastic modulus of Al-Cu-Ni, Al-Cu-Sn, and Al-Ni-Sn alloys is approximately 214.47, 35.11, and 75.61 GPa, respectively. Tensile properties of Cu-Ni-Sn and Al-Cu-Ni-Sn alloys could not be evaluated due to the inability to prepare specimens.

In corrosion property measurements, six alloys were fabricated, including four ternary and two quaternary alloys with equiatomic compositions. The corrosion potential of the alloys ranges from -0.06186 to 0.80445 (V/cm2), with the lowest observed in the Al-40at.%Cu-20at.%Ni-20at.%Sn alloy and the highest in the Al-Ni-Sn ternary alloy, exhibiting the best corrosion resistance. Anodic polarization curves show passivation phenomena only in Al-Cu-Ni and Al-20at.%Cu-20at.%Ni-20at.%Sn alloys.

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