時效熱處理對於CoCrNiAlTiB 中熵合金微觀結構與機械性質影響之研究;Effect of Aging on the Microstructure and Mechanical Properties of CoCrNiAlTiB medium-entropy Alloy

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Title:	時效熱處理對於CoCrNiAlTiB 中熵合金微觀結構與機械性質影響之研究;Effect of Aging on the Microstructure and Mechanical Properties of CoCrNiAlTiB medium-entropy Alloy
Authors:	陳顥;Chen, Hao
Contributors:	機械工程學系
Keywords:	中熵合金;晶粒細化;時效處理;L12相;Medium-entropy alloy (MEA);Grain refinement;Aging treatment;L12 phase
Date:	2025-07-23
Issue Date:	2025-10-17 13:05:48 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究旨在探討硼元素摻雜對五元中熵合金(Co43Cr15Ni30Al5Ti7)99.7B0.3之微觀組織與機械性質所造成之影響，並評估不同熱處理參數（再結晶溫度與時間、時效溫度與時間）對材料性能的調控效果。實驗設計包含 900 °C 再結晶處理（2、4、6、8 小時）與 700 °C、750 °C 不同時效條件之組合，並利用高溫熱示差掃描量熱儀（DSC）、穿透式電子顯微鏡（TEM）、電子背向散射繞射（EBSD）、能譜分析（EDS）與X光繞射（XRD）等技術，系統性分析其晶粒演變行為與析出機制，搭配硬度及拉伸試驗評估其力學性質。研究結果顯示，硼元素在晶界的偏析行為可有效抑制晶粒成長，達到晶粒細化與提升基體強度之效果。在相同熱處理條件（900 °C-4 h + 750 °C-8 h）下，B0合金晶粒尺寸為 678 nm，而 B0.3合金可細化至 359 nm，顯示微量硼摻雜對晶界遷移的抑制作用明顯。時效後可析出具晶格整合性之 L12析出相，其形貌呈現球狀，尺寸介於14 - 44 nm之間，為提升強度與維持延性的關鍵。機械性質方面，短時再結晶（2 - 4小時）搭配中等時效條件（如750 °C-4h）可獲得高強度組合，不同熱處理條件展現良好的強韌性調控彈性，適合針對應用需求進行調整，例如，在 900 °C-4 h + 750 °C-8 h 條件下，B0.3合金可達成1681 MPa之降伏強度與20.5%延性。本研究建立了中熵合金中微量硼摻雜對晶粒尺寸與析出行為之影響機制，並證明熱處理參數對機械性質具有效的調控能力。透過結合元素設計與製程控制，可實現具高強度與良好延性的中熵合金材料，為未來高性能合金之設計提供依據。 ;This study aims to investigate the effects of boron (B) addition on the microstructure and mechanical properties of the (Co43Cr15Ni30Al5Ti7)B0.3medium-entropy alloy. To enhance the mechanical properties, different parameter of recrystallization and aging heat treatment had been conducted. The experimental design involves 900 °C recrystallization treatments for 2, 4, 6, and 8 hours, followed by aging treatments at 700 °C and 750 °C for various durations. A comprehensive analysis of grain evolution and precipitation behavior was conducted using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD), along with hardness and tensile testing to assess mechanical performance. The results show that boron element tends to segregate at grain boundaries, effectively suppressing grain growth, leading to refine grains and enhance the strength of the alloy. Under identical heat treatment conditions (900 °C-4 h + 750 °C-8 h), the B0 alloy exhibited an average grain size of 678 nm, while the B0.3 alloy demonstrated a finer grain size of 359 nm, indicating that even a minor addition of boron significantly hinders grain boundary migration. After aging process, spherical and coherent L12-ordered precipitates were observed, ranging from 14 to 44 nm in diameter, playing a critical role in strengthening while maintaining ductility. In terms of mechanical behavior, short-time recrystallization (2–4 h) combined with moderate aging conditions (e.g., 750 °C for 4 h) will exhibit high-strength performance. Varying the heat treatment parameters provides flexibility in tailoring strength-ductility combinations to meet specific application needs. For instance, the B0.3 alloy reached a yield strength of 1681 MPa and an elongation of 20.5% under the 900 °C-4 h and 750 °C-8 h condition. Overall, this study elucidates the mechanisms by which minor boron additions influence grain size and precipitation in medium-entropy alloys and confirms the significant tunability of mechanical properties through heat treatment optimization. These findings provide valuable guidance for the design of high-performance alloys through integrated alloying and processing strategies.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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