本研究利用氣體霧化法製備Al0.5CoCrFeNi2之高熵合金粉末，改善常見之電弧熔煉或感應熔煉所製備之塊材須反覆重熔問題，氣體霧化法與其他製程相比，製備效率較快，可使元素成份均勻分佈，準確控制化學組成，且可保持高溫初始相之晶體結構，研究目的主要探討退火熱處理對於微觀結構、相變化與機械性質之影響，再進一步與商用常見之Incoloy 825進行高溫氧化及耐腐蝕性之比較；由於氣體霧化法快速冷卻之製程，使此合金擁有高溫初始相FCC結構，與文獻計算模擬產生之相圖所顯示高溫初始相FCC吻合，藉由連續升溫之In-situ XRD分析結果顯示，從室溫加熱至1200℃皆無相變化產生，然而透過DSC結果發現溫度於1000℃時發生相變化，表示短時間溫度改變對於此合金產生相變化之驅動力較低，因此利用退火熱處理以逐漸增加持溫時間使其產生相變化，進而控制析出相之比例，從相異退火時間之XRD顯示，當退火48小時才有繞射峰產生，藉由SEM及EDS發現經退火熱處理後，從此合金之晶界析出富含Cr之析出物，隨退火時間增加，析出物成核成長所佔據之面積漸增，直至48小時析出物才於XRD中顯示出繞射峰，再利用EBSD進行結晶取向之相鑑定，發現此合金相變化前之FCC相結晶排列傾向Ni3Al晶體結構，經退火發生相變化後，FCC相之結晶排列仍為Ni3Al晶體結構，而析出相之結晶排列則傾向NiAl及Fe之BCC晶體結構，而退火後整體平均硬度為4.22 GPa與未退火之硬度值4.25 GPa接近，並無因為退火造成機械性質下降；再與Incoloy 825進行高溫氧化及耐腐蝕性之比較，將此合金於鹽酸環境中進行動電位極化，發現測量值Ecorr為 -212 mV、 Icorr為1.5 μA/cm2，而Incoloy 825測量值Ecorr為 -239 mV、 Icorr為5.16 μA/cm2，此合金於酸性環境中具較出色之耐腐蝕性，而高溫氧化行為則置於900℃空氣氛圍中進行，發現此合金之氧化速率明顯比Incoloy 825緩慢，表示此合金之高溫抗氧化能力優於Incoloy 825。

In this study, Al0.5CoCrFeNi2 high-entropy alloy powders were prepared by gas atomization process to overcome the problems of bulk prepared by arc or induction melting. Compared with other processes, this process has better efficiency to obtain the powders with uniform elements distribution and precise chemical composition. Moreover, it can also preserve the high temperature phase. The purpose of this study was to discuss the effect of annealing treatment on the microstructure, phase transformation and mechanical property. In addition, this alloy was compared with the Incoloy 825 on high-temperature oxidation behavior and corrosion resistance properties. Due to the rapid cooling rate of gas atomization, this alloy had a high-temperature initial FCC phase. The In-situ XRD results indicated that phase transform did not occur from RT. to 1200℃. However, the DSC results indicated the phase transformation was at 1000℃. Therefore, annealing treatment was adjusted to gradually increase the annealing time to make phase transformation. From the XRD of the different annealing times, diffraction peaks began to generate after 48 hours. After annealing process, With SEM and EDS analysis the results showed the Cr-rich precipitated from the grain boundaries of this alloy, and the longer the annealing time, the more the precipitates. Then, EBSD was used to identify the crystal orientation of the phase, it was found that the FCC phase tended to form the Ni3Al crystal structure before the phase transformation. After the phase transformation during annealing, the crystal arrangement of FCC phase was still the Ni3Al, and the precipitate phase tended to form the BCC crystal structure of NiAl and Fe. The average hardness was 4.22 GPa after annealing treatment, which was close to the hardness value of 4.25 GPa before heat treatment. Compared with Incoloy 825 on high temperature oxidation and corrosion resistance, the alloy obtained Ecorr = -212 mV and Icorr = 1.5 μA/cm2 while Incoloy 825 obtained Ecorr = -239 mV and Icorr = 5.16 μA/cm2, the alloy had excellent corrosion resistance in acid environment. The high temperature oxidation experiment was sequentially conducted in air furnace at 900℃. It was found that the oxidation rate of the alloy was significantly slower than Incoloy 825, indicating that the high temperature oxidation resistance of the alloy was outstanding.

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