高熵合金因其具有良好的機械性能和應用價值成為當今研究的熱門題目，對於航太、車輛、能源、醫療、國防等，所需金屬材料性質之需求更是與日俱增，因此如何突破目前金屬材料於各領域使用的性質上限是一大重要的考量。其中高降伏強度且具有一定延性的合金是一個重要的指標，而根據前人之研究中，Co43Cr15Ni30Al5Ti7五元中熵合金，在經過適當之熱處理製程後將具有超高強度(~2100MPa)及延性(~10%)之組合，故在本研究中將以優化熱處理製程及硼元素的摻雜對於機械性質的影響來作為研究。 此研究通過將硼元素以0.1~0.4 at. %微量摻雜至Co43Cr15Ni30Al5Ti7五元中熵合金中，以電弧熔煉並使用墜落式鑄造鑄成具有單一FCC相之合金板材，並對其進行1000℃-6小時的均質化熱處理，而後將合金板材冷滾軋80%，再以不同溫度及時間進行再結晶熱處理，最後將試片進行機械性質分析。 實驗結果顯示合金經900℃-2小時再結晶退火後，可獲得最適合的降伏強度與延性之組合，所以該熱處理條件根據定為爾後摻雜不同硼含量合金研究之熱處理參數。另外，對摻雜不同比例硼元素之中熵合金再進行750℃-4小時的時效處理以析出L12相。透過L12結構之析出物與FCC相之基地整合(Coherent)的效果，進一步的提升降伏強度並保留其延性。 最後根據研究結果之機械性質及分析硼元素摻雜之效果得知，經過900℃-2小時再結晶退火加上750℃-4小時之時效熱處理的試片，其中摻雜0.3 at. %硼元素的中熵合金將具有最佳的機械性能，其降伏強度為1817MPa、最大抗拉強度為2313MPa，且具有14.5%的延性，而比強度更是高達288 MPa‧cm3/g。 ;High-entropy alloys (HEAs) have become a hot topic in research today due to their excellent mechanical properties and practical applications. There is a growing demand for metallic materials with specific properties in aerospace, automotive, energy, medical, defense, and other industries. Therefore, it is very important to break through the current limits of metallic material properties in various fields. High yield strength combined with a certain level of ductility is a crucial indicator. According to previous studies, the Co43Cr15Ni30Al5Ti7 quinary HEA after appropriate heat treatment processes is expected to achieve a combination of ultra-high strength (~2100 MPa) and ductility (~10 %). This study aims to optimize the heat treatment process and investigate the impact of boron doping on the mechanical properties of this quinary HEA. In this research, boron elements were added in trace amounts (0.1~0.4 at.%) to the Co43Cr15Ni30Al5Ti7 HEA. The alloy was arc-melted and cast into single-phase FCC alloy plates using drop-casting. The alloy plates underwent homogenization heat treatment at 1000°C for 6 hours, followed by cold rolling to 80% reduction. Subsequently, recrystallization heat treatment was performed at different temperatures and durations to analyze their mechanical properties. Experiment showed that the optimal combination of yield strength and ductility was achieved after annealing at 900°C for 2 hours. This annealing parameter was then used for further study on the alloys with different additions of boron doping. The alloys with different addition of boron doping were aged at 750°C for 4 hours to precipitate L12 phase after recrystallization annealing. The coherent integration of L12 precipitates with the FCC matrix further enhanced the yield strength while maintaining ductility. Based on the research results and analysis of mechanical properties influenced by boron doping, it is determined that the high-entropy alloy after cold rolled 80% then treated with 900°C for 2 hours and followed by aging at 750°C for 4 hours exhibits the best mechanical performance. Specifically, the alloy doped with 0.3 at.% boron achieves an optimal yield strength is 1817MPa, its maximum tensile strength is 2313MPa, and it has a ductility of 14.5%, the specific strength is as high as 288 MPa‧cm3/g.
