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標題: | L12析出強化型中熵合金(CrCoNi)94Al3Nb3之顯微結構與機械性質分析 Microstructure and Mechanical Properties Characterization of L12-precipitate Hardening (CrCoNi)94Al3Nb3 Medium-entropy-alloy |
作者: | 駱炯源 Chiung-Yuan Lo |
指導教授: | 楊哲人 Jer-Ren Yang |
關鍵字: | 中熵合金,析出強化,顯微結構分析, Medium-entropy alloy,precipitate hardening,microstrcuture characterization, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 高熵合金擁有優異的機械性能,其中以CrCoNi三元中熵合金表現最為突出。然而,單相面心立方高熵合金與中熵合金的降伏強度僅有200 MPa至500 MPa,並不適合應用於需要高降伏強度的環境中。因此,本研究設計L12析出強化中熵合金(CrCoNi)94Al3Nb3,透過在700°C和800°C進行時效處理,在FCC基底中引入均勻分布的L12-Ni3(Al,Nb)奈米析出物,以提高FCC型的中熵合金的降伏強度和機械性能。在微結構分析顯示顯示,L12-Ni3(Al,Nb)的尺寸約為5至10奈米且在FCC基底當中分布的非常均勻,此外,也發現尚未被報導過的δ相轉變與HCP相生成。在拉伸試驗中,經過700oC尖峰時效處理後降伏強度和極限拉伸強度分別達到1412 ± 22 MPa與1553 ± 45 MPa,且伸長率達到7.8 ± 0.94 %。在霍普金森快速撞擊試驗中,相較於未進行析出的中熵合金FeCrCoNi,(CrCoNi)94Al3Nb3在相同真實應變量下,達到約2600MPa的真實應力,約為FeCrCoNi的兩倍強度,展現其優異的衝擊性能。在變形組織分析中,本研究,探討L12析出物與缺陷、疊差和變形雙晶之間的相互作用,也探討造成材料延展性下降與高降伏強度的因素。 High-entropy alloys (HEAs) exhibit excellent mechanical properties, with the CrCoNi ternary medium-entropy alloy being particularly outstanding. However, the yield strength of single-phase face-centered cubic (FCC) high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) ranges approximately from 200 MPa to 500 MPa, which is not suitable for applications requiring high yield strength. Therefore, in this study, a L12 precipitate-hardening MEA, (CrCoNi)94Al3Nb3, was designed. Through aging treatments at 700°C and 800°C, uniformly distributed L12-Ni3(Al,Nb) nanoscale precipitates were introduced into the FCC matrix to enhance the yield strength of the FCC-type MEA. Microstructure analysis revealed that the L12-Ni3(Al,Nb) precipitates had sizes of approximately 5 to 10 nanometers and were distributed very uniformly within the FCC matrix. Additionally, the transformation of δ phase and the generation of hexagonal close-packed (HCP) phase were also observed. In tensile tests, after peak aging treatment at 700°C, the yield strength and ultimate tensile strength reached 1412 ± 22 MPa and 1553 ± 45 MPa, respectively, with an elongation of 7.8 ± 0.94%. In Hopkinson bar impact tests, (CrCoNi)94Al3Nb3 demonstrated a true stress of approximately 2600 MPa with 20% true strain, showing twice the strength of FeCrCoNi and exhibiting excellent impact performance compared to the non-precipitated medium-entropy alloy FeCrCoNi. In the deformation microstructure analysis, this study explored the interactions between L12 precipitates and defects, stacking faults, and deformation twins. It also investigated the factors contributing to the reduction in material ductility and the high yield strength. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/88815 |
DOI: | 10.6342/NTU202302391 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 材料科學與工程學系 |
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