高熵合金由五元或五元以上的元素組成，且每種元素的比例在5 at.%到35 at.%之間，其相對於一般合金而言較容易形成單一固溶體且結構簡單，這些高熵合金體系具有優異的物理化學性能，如高強度和硬度、良好的耐腐蝕性及熱穩定性，由於其極具潛力以及豐富的合金設計前景，高熵合金為金屬的開發帶來新的突破及想像。其中等莫耳比鈷-鉻-鐵-錳-鎳高熵合金由Cantor等人首先提出，它們具有單一的FCC相結構且具有出色的穩定性和拉伸性能，在低溫液態氮中 (77 K) 也不易脆化。
本研究中為了探討鎳含量對鈷-鉻-鐵-錳-鎳高熵合金系統的影響，利用CALPHAD (Calculation of Phase Diagram) 計算方法來模擬合金的組成。本研究首先使用Pandat軟體並搭配PanHEA資料庫，計算鎳元素比例為5~35 at.%之高熵合金，總共七個組成；在Scheil模擬結果顯示，合金1在鎳含量為5 at.%時由兩相FCC與BCC相所組成，其餘的合金2~7皆為單一FCC相，而在Lever Rule模擬中則顯示合金1~7於1000°C皆為單一FCC相，結果顯示鎳的增加有助於形成FCC穩定相。接著將模擬結果搭配實驗的方式進行驗證，本實驗使用高純度99.9 wt.% 鈷、鉻、鐵、錳、鎳金屬，利用電弧熔融製備合金，為了進行比較分析，將合金切半，一半做為鑄態合金，另一半在1000°C下進行240小時的熱處理。最後，分別用高解析度場發射掃描式電子顯微鏡 (FE-SEM) ，搭配能量散射X射線分析儀 (EDS) 、X射線繞射儀 (XRD)、穿透式電子顯微鏡 (TEM) 及電子能譜儀 (XPS) 鑑定其顯微組織、相結構及金屬氧化物等組成。
本研究亦針對鈷鉻鐵錳鎳高熵合金進行腐蝕電化學實驗及維氏硬度測試，根據極化曲線結果，可以發現大致上合金於熱處理前的腐蝕速率都略小於熱處理後的合金，其中合金5在熱處理前有最小的腐蝕速率為 〖1.54×10〗^(-3)(mm year-1)。而在硬度的表現上，合金1因為有富含鉻的第二相，因此其硬度值最高，為254 Hv。
從模擬及實驗結果可以得知，本研究除了合金1 (鎳元素比例為5 at.%) 含有其他相結構並同時具有氧化物，其餘合金 (鎳元素比例為10~35 at.%) 從實驗得到的結果與Pandat相圖模擬軟體計算所預測的結果有高度的吻合。

High-entropy alloys have five or more elements as their major constituents, and the contents of each element is greater than 5 at.% and less than 35 at.%. It is easy to form single solid solution, having simple structure. High-entropy alloys have excellent physical, chemical and mechanical properties, such as high strength and hardness, excellent corrosion resistance and thermal stability. Because high entropy alloys have potentially and various desirable properties, it takes new imagination and innovation for developing the novel alloys. Equimolar Co-Cr-Fe-Mn-Ni high entropy alloy put forward by Cantor et al. has single FCC structure, excellent stability and tensile strength, it will also not embrittlement at liquid nitrogen (77k).
To research the influence of Nickle to Co-Cr-Fe-Mn-Ni high entropy alloy system, we used the CALPHAD method to calculate the constituents of alloys. In this research, the Pandat software with the PanHEA database was used for simulation. We chose CoyCryFeyMnyNix (x= 5, 10, 15, 20, 25, 30 and 35 in atomic percent) seven groups to study. First, the results of Scheil model showed that alloy 1 with 5 at.% Ni has two phase, FCC and BCC, the others were all single FCC phase. In Lever Rule model, all seven alloys were single FCC phase at 1000°C. The increase of Ni will enhance the form of FCC phase.
In this study, we used the metals with purity of 99.9 wt.%, and the alloys were prepared by an arc melting furnace, half sphere of each sample was followed by heat treatment at 1000°C for 240 hours, the other half were as-cast samples. Finally, the microstructure and composition of them were analyzed by the field-emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS).
In this research, corrosion experiments and Vickers hardness tests were carried out on Co-Cr-Fe-Mn-Ni high entropy alloys. According to the experimental results, the corrosion rates of the alloys before heat treatment are slightly lower than that of the alloy after heat treatment. Among them, alloy 5 has the lowest corrosion rate, and the value is 〖1.54×10〗^(-3)(mm year-1). The results of hardness, because alloy 1 has the second phase that is rich of chromium, the value of hardness is the highest, which is 254 Hv.
The result of calculation and experiment indicated that the seven alloys were mainly composed of FCC structure. However, alloy 1 had two phases after heat treatment. For the other alloys, the calculation results were mostly consistent with experimental results.
Keywords: high-entropy alloys; calculation of phase diagrams (CALPHAD) method; Co-Cr-Fe-Mn-Ni alloy system; electrochemical corrosion; Hardness

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