臺灣博碩士論文加值系統

本研究探討NdFeB MQ2-14-175及MQ2-14-150磁石經不同熱變形製程後對MQ3磁石微觀組織及磁性之影響。第一部分探討熱變形溫度及應變速率的效應影響。結果顯示不同型號磁石因為成份的差異，其最佳製程條件也不一樣。對於型號14-175而言，最佳製程條件為在溫度780 oC下壓製240 s (strain rate為5*10-3 s-1)，其磁特性為Br = 13 kG、iHc = 19.7 kOe、(BH)max = 42.4MGOe、iHc+(BH)max = 62.1；對於型號14-150磁石而言，最佳製程條件為在溫度830 oC下壓製240 s (strain rate為5*10-3 s-1)，此時磁特性可達Br = 13.5 kG、iHc = 16.4 kOe、(BH)max = 45 MGOe、iHc+(BH)max = 61.5。第二部分探討微觀組織對MQ3磁石磁特性的影響，結果顯示利用光學顯微鏡所觀察到的薄帶厚度變化，無法作為影響磁石磁特性的主要依據，反之利用SEM觀察的晶粒形貌及大小變化，發現當MQ3磁石中心位置之長軸晶粒拉伸變化率，Σ，介於4-4.5時，磁石有最佳的磁特性。此結果與XRD分析晶粒(00L)配向度變化趨勢相吻合，說明MQ3磁石適當的長軸晶粒拉伸率才是影響磁特性的主要因素。第三部分探討升溫速率及底模高度的改變對磁石磁特性的影響。實驗結果顯示，當升溫速率從2 0C/s提升至4.3 0C/s，縮短了磁石在高溫停滯的時間，減少富釹相的揮發，致使磁石磁性可提升並達Br = 13.6 kG、iHc = 17.5 kOe、(BH)max = 46 MGOe、iHc+(BH)max = 63.5。又改變磁石位於感應線圈中的位置可使磁石內部受熱更均勻。另外，二段升溫曲線可有效縮短磁石在高溫的持溫時間及提升MQ2磁石受熱的均勻性，使其在變形時有較低的流變應力(flow stress)，在溫度800 0C下壓製240 s下，磁石磁特性可達Br = 13.5 kG、iHc = 17.6 kOe、(BH)max = 45 MGOe、iHc+(BH)max = 62.6。

The effects of hot deformation processes, including heat treatment condition and strain rate, on magnetic properties and microstructure of MQ3 magnets made from two kinds of MQII magnets (Model: 14-175 & 14-150) were reported. At first, various hot deformation temperatures on the magnetic properties of hot-deformed MQ3 magnets were studied. For 14-175 sample, Br of 13 kG, iHc of 19.7 kOe, (BH)max of 42.4MGOe, and iHc+(BH)max of 62.1 were obtained in 780 oC, 240 s (strain rate = 5*10-3 s-1) hot-deformed magnet. On the other hand, for 14-150 sample, Br of 13.5 kG, iHc of 16.4 kOe, (BH)max of 45 MGOe, and iHc+(BH)max of 62.1 were obtained in 830 oC, 240 s (strain rate = 5*10-3 s-1) hot-deformed magnet. The optimal fabrication condition is different due to different composition of two kinds of MQII samples. Secondly, the effect of microstructure on the magnetic properties of hot-deformed magnets was also studied. The morphologies of melt spun flakes of the hot-deformed magnets were observed by optical microscope. However, simply from the change of flakes thickness could not explain the change of their magnetic properties. In contrast, the ratio of the change of long axis of the grains of MQ3 magnet and the diameter of original MQ2 magnet,Σ, is analyzed by SEM for the middle part of the magnets. It is found that the MQ III magnets with the optimal magnetic properties have the value Σ from 4 to 4.5. Thirdly, the effect of heating rate and the position of the magnet in induction coil were studied. As the heating rate rises from 2 0C/s to 4.3 0C/s, the optimum Br of 13.6 kG, iHc of 17.6 kOe, (BH)max of 46 MGOe, and iHc+(BH)max of 63.5 can be obtained. Meanwhile, the magnets pressed at the center part of the induction coil showed better microstructure homogeneity and magnetic properties than those magnets pressed at lower part of the induction coil. In addition, applying two-stage heating process before hot deformation may reduce the time of hot pressing and also lead to the much uniform microstructure of the hot deformed magnets, due to the reduction of flow stress during hot deformation. The optimal properties Br of 13.5 kG, iHc of 17.6 kOe, (BH)max of 45 MGOe, and iHc+(BH)max of 62.6 can be obtained for 800 0C, 240 s, accordingly.

摘要 I
Abstract II
致謝 IV
目錄 V
圖目錄 VIII
表目錄 XIV
第一章 緒論 1
1-1 前言 1
1-2 磁性材料的分類與簡介 2
1-3 稀土永久磁石簡介 5
1-3-1 永久磁石發展歷史 5
1-3-2 第一代稀土永久磁石-RCo5 6
1-3-3 第二代稀土永久磁石-R2TM17 8
1-3-4 第三代稀土永久磁石-RFeB 10
1-4 R2Fe14B化合物晶體結構之簡介 12
1-5 熱變形NdFeB磁石簡介 14
1-5-1 合金融煉與鑄錠 15
1-5-2 快淬薄帶 15
1-5-3 合金製粉 16
1-5-4 MQ1、MQ2、MQ3製程 18
1-5-5 機械加工與後續處理 21
1-6 熱變形釹鐵硼磁石文獻回顧 22
1-7 研究動機與目的 27
第二章 理論基礎 29
2-1 磁性來源 29
2-2 磁滯曲線 31
2-3 物質的磁性分類 33
2-4 磁異向性(Magnetic anisotropy) 37
2-5 稀土永磁的矯頑機制 39
2-5-1 反向磁區孕核成長型 40
2-5-2 磁區壁栓固型機制 41
2-5-3 單磁區/微晶型機制 41
2-6 晶粒大小對本質矯頑磁力的影響 42
2-7 磁粒子大小對磁性的影響 44
2-8 熱變形NdFeB之織構成形機制[54] 46
2-8-1 變形機制 46
2-8-2 流變應力 48
2-8-3 翻轉機制 50
第三章 實驗方法 52
3-1 實驗流程 52
3-2 MQ2磁石特性及成份 53
3-3 MQ3磁石製程參數 57
3-4 真空熱壓機 60
3-5 分析與量測 61
3-5-1 切割與研磨 61
3-5-2 XRD-結構鑑定 62
3-5-3 B-H tracer 磁性量測 63
3-5-4 金相觀察 63
3-5-5 SEM-微觀組織觀察 64
3-5-6 磁石應變模擬 65
第四章 實驗結果與討論 66
4-1 14-175 MQ2磁石經熱變形後之MQ3磁石特性變化 66
4-1-1 熱變形溫度之影響 66
4-1-2 應變速率之影響 71
4-2 14-150 MQ2磁石經熱變形後之MQ3磁石特性變化 77
4-2-1 熱變形溫度之影響 77
4-2-2 應變速率之影響 83
4-3 以光學顯微鏡進行顯微結構觀察 87
4-3-1 光學顯微鏡觀察金相結構 87
4-3-2 磁石應變模擬 90
4-3-3 金相顯微結構對磁特性之影響 95
4-4 以SEM進行微觀組織觀察 97
4-4-1 SEM觀察微觀組織 97
4-4-2 晶粒大小對磁特性之影響 103
4-5 熱變形製程條件之優化 107
4-5-1 升溫速率對磁石磁特性的影響 107
4-5-2 磁石於感應線圈內高度之效應 113
4-5-3 二段升溫曲線對磁石磁特性的影響 116
第五章 結論 121
第六章 參考文獻 124

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