臺灣博碩士論文加值系統

燒結釹鐵硼永久磁石是目前最高磁性能的永磁材料，近年來在電動車及離岸風力發電設施用途日益漸增。應用於上述設施之磁石必須具備高熱穩定性預防工作溫度過高造成熱退磁現象，可藉由提高磁石的矯頑磁力增加磁石的抗退磁能力。Dy核殼結構形成的高磁晶各向異性可以大大提高燒結NdFeB磁體的矯頑磁力。常見晶界擴散(GBD)方式以塗佈、濺射、沉積法等方式將稀土元素、合金或化合物覆於磁石表面再進行熱處理，可使重稀土元素在高溫下沿著晶界向磁石內部擴散; 然而，此方式造成磁石表面稀土濃度過高致使形成「晶內擴散」，反而使磁石的最大磁能積下降。此外，磁石表面在趨入擴散熱處理結束後會殘留未擴散完之HRE結晶造成額外浪費。儘管蒸鍍晶界擴散法可避免磁石表面之重稀土殘留，但傳統蒸鍍晶界擴散法之蒸發量少，Dy元素不易覆於燒結釹鐵硼永久磁石表面，磁特性提升效果不佳。另一方面，傳統蒸鍍晶界擴散法使大量HRE元素沉積於沉積系統，如在真空室和處理容器的內壁上，也造成製程成本增加。本研究對應用Dy蒸鍍晶界擴散法獲得之燒結NdFeB永久磁石在不同時間、溫度和溫度梯度的驅入擴散熱處理下的HRE(重稀土元素)分佈和整體磁性能進行了評價。研究中分別使用電子探針顯微分析儀 (EPMA)、輝光放電光譜儀 (GDS) 和磁滯迴線儀研究了燒結 Dy 擴散 NdFeB 永磁體的 HRE 分佈和磁性能。研究結果顯示，以850℃→950℃之趨入擴散溫度梯度進行10小時Dy晶界擴散熱處理，獲得最佳綜合磁特性，其磁特性量測結果為iHc=1415 kJ/m及(BH)max=394.1 kJ/m3，達N52H等級; 而未經處理之釹鐵硼永久磁石，其磁特性量測結果則為iHc=1105 kJ/m及(BH)max=400.3 kJ/m3，為N52M等級。相較之下，本研究之最佳製程條件所獲得釹鐵硼永久磁石之iHc 及BHH (i.e., BHH= iHc + (BH)max)分別高於未經處理之釹鐵硼永久磁石21.9 %及16.8%。本研究將為透過控制晶界擴散過程中的溫度梯度開發具有高本質矯頑力的低重稀土燒結NdFeB磁石提供啟示，使之更適合應用於全球積極推動之電動車及離岸風力發電機等之重要節能設施中。

Sintered NdFeB permanent magnet is the permanent magnet material with the highest magnetic performance at present. In recent years, it has been increasingly used in electric vehicles and offshore wind power facilities. The magnets used in the above facilities must have high thermal stability to prevent thermal demagnetization caused by high working temperature, and the anti-demagnetization ability of the magnets can be increased by increasing the intrinsic coercivity of the magnets. The high magnetocrystalline anisotropy formed by the core-shell structure of Dy could significantly enhance the intrinsic coercivity of the sintered NdFeB magnets. The traditional grain boundary diffusion (GBD) method covers the rare earth elements, alloys or compounds on the surface of the magnet by coating, sputtering, deposition, etc. and then heat treatment. In this way, the heavy rare earth elements will diffuse along the grain boundary to the inside of the magnet at high temperature; however, this method leads to an excessively high rare earth concentration on the surface of the magnet, resulting in the formation of "intragranular diffusion", which reduces the maximum magnetic energy product of the magnet. In addition, undiffused HRE residues will remain on the surface of the magnet after the diffusion heat treatment is completed, resulting in additional waste. Although the evaporation grain boundary diffusion method can avoid heavy rare earth residues on the surface of the magnet, the evaporation amount of the traditional evaporation grain boundary diffusion method is small, and the Dy element is not easy to cover the surface of the sintered NdFeB permanent magnet, and the effect of improving the magnetic properties is poor. On the other hand, the traditional vapor deposition grain boundary diffusion method causes a large amount of HRE elements to be deposited on the deposition system, such as on the inner wall of the vacuum chamber and the processing container, which also increases the process cost. In this research, the evaluation of HRE (i.e., heavy rare-earth-elements) distribution and magnetic properties of sintered NdFeB permanent magnets obtained by applying Dy evaporation grain boundary diffusion method under different time, temperature and temperature gradient of the drive-in diffusion heat treatment is discussed. HRE distribution and magnetic properties of the sintered Dy-diffused NdFeB permanent magnets was investigated by investigated using an electron probe microanalyzer (EPMA), glow discharge spectrometer (GDS) and hysteresis loop meter, respectively. The results show that the best magnetic properties are obtained under the temperature gradient of 850℃→950℃ for 10 hours of Dy grain boundary diffusion heat treatment. The measured magnetic properties of the sintered Dy-diffused NdFeB permanent magnets are iHc =1415 kJ/m and (BH)max =394.1 kJ/m3, reaching N52H grade, while the magnetic properties of untreated NdFeB permanent magnets are iHc =1105 kJ/m and (BH)max=400.3 kJ/m3, which is N52M grade. In contrast, the iHc and BHH (i.e., BHH= iHc + (BH)max) of the NdFeB permanent magnets obtained under the optimal process in this study were 21.9 % and 16.8 higher than those of the untreated NdFeB permanent magnets, respectively. The novel manufacturing method proposed in this study can not only effectively improve the utilization of heavy rare earths but also enhance the overall magnetic properties. This research would shed light on developing low heavy rare earth sintered NdFeB magnets with high intrinsic coercivity through controlling the temperature gradient in the grain boundary diffusion process, making them more suitable for important energy-saving facilities such as electric vehicles and offshore wind power generators that are actively promoted around the world.

目錄
摘要 i
Abstract iii
致謝 vi
目錄 vii
圖目錄 x
表目錄 xi
符號說明 xii
第一章 緒論 1
1.1前言 1
1.2 硬磁磁石 3
1.3釹鐵硼磁石介紹 4
1.4 釹鐵硼磁石製程 5
1.4.1氫碎(HD) 6
1.4.2氣流粉碎(JM) 7
1.4.3磁場成行 7
1.4.4冷均壓成型(CIP) 8
1.4.5真空燒結 8
1.4.6熱處理 11
1.4.7加工與表面處理 11
1.4.8充磁 11
1.5晶界擴散(Grain Boundary Diffusion，GBD) 14
1.5.1表面塗佈的HAL(High-Anisotropy field Layer) 14
1.5.2蒸鍍 15
1.5.3蒸發 15
1.6晶界擴散(GBD)滲Dy文獻回顧 16
1.7研究動機與目的 18
第二章 磁性理論 20
2.1磁性 20
2.2磁性分類 21
2.2.1.鐵磁性(ferromagnetism) 21
2.2.2. 陶鐵磁性(ferrimagnetism) 22
2.2.3.反鐵磁性(antiferromagnetism) 22
2.2.4.順磁性（paramagnetism） 22
2.2.5.抗磁性(diamagnetism) 22
2.3磁滯曲線 24
2.4磁各向異性 27
2.5稀土永磁之矯頑機制 29
2.5.1.反向磁疇孕核成長型 30
2.5.2.磁疇壁栓固型 30
2.5.3.單磁疇型和微晶型 30
2.6粒徑大小對矯頑磁力之影響 32
2.6.1.磁粒子大小 32
2.6.2.晶粒大小 33
2.7擴散理論 34
第三章 實驗方法 37
3.1實驗流程 37
3.2擴散原重稀土之選用 39
3.3晶界擴散 44
3.4分析與量測 45
3.4.1 B-H tracer 磁特性量測 45
3.4.2 電子微探儀(EPMA)微觀組織觀察 46
3.4.3輝光放電發射光譜儀(General information about ,GDOES) 47
第四章 結果與討論 49
4.1晶界擴散熱處理時長及溫度對磁特性之影響及微觀結構分析 49
4.1.1 900℃下分別針對10小時及20小時之Dy晶界擴散趨入擴散熱處理實驗 49
4.1.2 850℃及950℃10小時Dy晶界擴散熱處理的溫度之磁性能趨勢變化 53
4.2最佳化晶界擴散熱處理條件 57
4.2.1 增加於900℃趨入擴散溫度下進行15小時Dy晶界擴散熱處理之實驗條件 57
4.2.2不同溫度梯度之趨入擴散之實驗條件 61
第5章 結論 67
參考文獻 68

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