晶界擴散法對燒結釹鐵硼磁石本質矯頑磁力提升之研究

Improvement of coercivity of sintered NdFeB permanent magnets by grain boundary diffusion process

陳建甫(Chien-Fu Chen)

指導教授 ： 張文成

國立中正大學/理學院/物理學系/碩士(2013年)

摘要

本實驗第一部分先探討晶界擴散法提升燒結NdFeB磁石本質矯頑磁力之研究，分別對表面粗糙度、氧含量、磁石厚度、擴散溫度及持溫時間等因素進行相關的討論。實驗中指出使用砂紙研磨磁石表面，可降低表面粗糙度且拋除氧化物，有利於鏑之晶界擴散及提升磁石本質矯頑磁力。又氧含量低的磁石有助於鏑原子沿晶界擴散，本質矯頑磁力提升的效果較好，但殘留磁束密度及最大磁能積稍微減少。厚度較薄的磁石，晶界擴散效力可達大部分斷面，有效改善磁石深層處晶粒的磁異向性場。對已二段熱處理磁石再進行鏑晶界擴散之最佳擴散條件為900 oC 4小時，iHc提升量為4.5 kOe， iHc + (BH)max可達67.6。
第二部分為研究未經二段熱處理磁石藉由塗布氟化鏑進行晶界擴散，探討對於磁石本質矯頑磁力提升之影響。實驗結果顯示，燒結後磁石其本質矯頑磁力提升量大於已經二段熱處理磁石，iHc提升量能高達6.2 kOe。
最後一部分為濺鍍鏑金屬層於磁石表面後進行晶界擴散，當濺鍍的鏑薄膜越厚，所提升的本質矯頑磁力越大，在濺鍍時間50分鐘下，膜厚可達10 μm，對於厚度2 mm磁石而言，進入磁體之鏑含量相當於磁石的1.75 wt %，此情況下磁石本質矯頑磁力提升達7.9 kOe，而其Br＝13.9 kG、iHc＝22.9 kOe、(BH)max＝48.2 MGOe、iHc + (BH)max＝71.1；相對厚度3.2 mm磁石而言，擴散進入磁體之鏑含量佔整體的1.39 wt %，本質矯頑磁力提升量亦可達6.8 kOe，其Br＝13.8 kG、iHc＝22.0 kOe、(BH)max＝48.1 MGOe、iHc + (BH)max＝70.1。

關鍵字

氟化鏑 ； 晶界擴散 ； 釹鐵硼磁石 ； 矯頑磁力

並列摘要

In this study, grain-boundary-diffusion (GBD) process via the usage of DyF3 powder on the surface of magnets was applied to the sintered NdFeB magnets. The effects of surface morphology, oxygen concentration, thickness and diffusion conditions on coercivity (iHc) of sintered NdFeB magnets have been studied. The results show that pre-polishment of the magnets is effectively for reducing the surface roughness of magnets, leading to the enhancement of iHc. In addition, the magnets with lower oxygen concentration are helpful for Dy diffusion and improve iHc, yet easier to decrease Br of the magnets. Meanwhile, the diffusion of Dy in thinner magnets may easily reach the deeper part and improve the magnetocrystalline anisotropy field of inner grains, iHc of the magnets is easily enhanced, accordingly. In this series samples, the optimal magnetic properties of iHc increment (∆iHc) =4.5 kOe and iHc + (BH)max=67.6 under the diffusion conditions of 900 oC, 4 hrs were obtained. Furthermore, Dy diffusion treatment was applied to the as-sintered magnets without post annealing. It was found that ∆iHc are larger than those magnets treated with two steps annealing. The largest ∆iHc can be up to 6.2 kOe in magnets without two steps annealing. Finally, we changed Dy source from DyF3 powder to Dy film and study the thickness effect of Dy film on ∆iHc of the sintered magnets. The results showed that the ∆iHc was enhanced effectively with increasing the thickness of Dy film. Interestingly, extremely high ∆iHc up to 7.9 kOe can be obtained by introducing 1.75 wt% Dy only to the magnet through this novel GBD method. The optimal magnetic properties of Br = 13.9 kG, iHc=22.9 kOe, (BH)max=48.2 MGOe and iHc + (BH)max=71.1 were obtained in 2-mm thick magnet, as well as Br = 13.8 kG, iHc=22.0 kOe, (BH)max=48.1 MGOe and iHc + (BH)max=70.1 in 3.2-mm thick magnet.

並列關鍵字

DyF3 ； grain boundary diffusion ； NdFeB magnets ； coercivity

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