本文選題：燒結(jié)Nd-Fe-B磁體 + 電泳沉積�。� 參考：《武漢大學(xué)》2016年博士論文

【摘要】：為滿足電動(dòng)汽車(chē)、風(fēng)力發(fā)電機(jī)、節(jié)能家電等新興領(lǐng)域?qū)ο⊥劣来挪牧系男枨�、促進(jìn)稀土資源的高效利用,提高磁體的綜合磁性能、減少高矯頑力磁體的重稀土使用量已成為燒結(jié)Nd-Fe-B磁體研究領(lǐng)域的重要目標(biāo)。本文發(fā)展了電泳沉積這一新興的晶界擴(kuò)散技術(shù),研究了關(guān)鍵工藝過(guò)程和稀土含量對(duì)磁體性能的影響規(guī)律,確定了重稀土化合物DyF3和TbF3的最佳擴(kuò)散工藝,優(yōu)化了不同稀土含量磁體的最佳擴(kuò)散量,闡明了擴(kuò)散磁體的矯頑力增強(qiáng)機(jī)制,研究了擴(kuò)散磁體的使役性能,制備了低重稀土高矯頑力的燒結(jié)Nd-Fe-B磁體,實(shí)現(xiàn)了重稀土的高效利用,對(duì)電泳沉積晶界擴(kuò)散磁體的規(guī)�；圃旌蛻�(yīng)用具有重要指導(dǎo)意義。主要研究成果如下：1.采用電泳沉積方法,在燒結(jié)Nd-Fe-B磁體表面成功制備出均勻、平整、厚度可控的重稀土化合物涂層。確定了電泳沉積晶界擴(kuò)散DyF3的最佳擴(kuò)散溫度和擴(kuò)散時(shí)間。通過(guò)控制溫度和時(shí)間等擴(kuò)散工藝參數(shù),磁體的矯頑力從16.1 kOe大幅提高到22.8 kOe。無(wú)重稀土磁體中添加少于1.2 wt.% Dy,磁體矯頑力的增加量高于6.5 kOe,重稀土利用效率比常規(guī)粉末冶金方法高三倍以上。精確表征了擴(kuò)散樣品中Dy濃度隨到磁體表面距離的變化關(guān)系,分析表明磁體矯頑力的增加與Dy元素的濃度和分布密切相關(guān)。通過(guò)微觀結(jié)構(gòu)的分析,闡明了矯頑力的增強(qiáng)機(jī)制：高溫?cái)U(kuò)散后,Dy元素主要沿晶界擴(kuò)散進(jìn)入磁體內(nèi)部,在主相晶粒外圍形成具有高磁晶各向異性場(chǎng)的(Nd, Dy)2Fe14B相,從而顯著提高磁體的矯頑力。此外,被Dy替代的Nd元素析出于晶界,晶界相變得更加連續(xù)均勻且增厚,使得相鄰主相晶粒之間的磁孤立作用增強(qiáng),進(jìn)一步提高了磁體的矯頑力。2.利用電泳沉積厚度可控這一優(yōu)勢(shì),系統(tǒng)研究了DyF3涂層厚度和磁體厚度對(duì)燒結(jié)Nd-Fe-B磁體磁性能和微觀結(jié)構(gòu)的影響,初步解決了晶界擴(kuò)散法僅適用于薄片磁體的局限性。隨著涂層厚度的增加,磁體的矯頑力從16.10 kOe逐漸增加到24.04 kOe。通過(guò)對(duì)涂層厚度的優(yōu)化,無(wú)重稀土磁體中擴(kuò)散少于1.3wt.%的Dy,磁體矯頑力可顯著提高8.0 kOe,與其他方法相比優(yōu)勢(shì)明顯。由于重稀土元素的擴(kuò)散深度有限,擴(kuò)散效果受限于磁體的厚度,研究發(fā)現(xiàn)磁體的矯頑力隨磁體厚度的增加逐漸降低。當(dāng)磁體厚度為8.5 mm時(shí),矯頑力增加量仍有3.26 kOe,優(yōu)于當(dāng)前見(jiàn)諸報(bào)道的最佳結(jié)果。從而進(jìn)一步證實(shí)電泳沉積法是一種能夠精確控制涂層厚度、經(jīng)濟(jì)高效的制備較厚的高矯頑力磁體的方法。3.采用電泳沉積TbF3的方法,系統(tǒng)研究了初始磁體稀土含量對(duì)晶界擴(kuò)散磁體的影響規(guī)律,闡明了重稀土元素的擴(kuò)散機(jī)制和擴(kuò)散磁體的矯頑力增強(qiáng)機(jī)制。磁性能結(jié)果表明,不同稀土含量磁體的矯頑力都隨著涂層厚度的增加先逐漸升高,而后趨于穩(wěn)定或者降低。稀土量為30wt.%的初始磁體獲得的矯頑力增加量最大,添加少于0.81 wt.% Tb時(shí),矯頑力提升10.07 kOe,實(shí)現(xiàn)了重稀土的高質(zhì)化利用。微觀結(jié)構(gòu)分析表明稀土量為30wt.%的初始磁體中,稀土量較低,晶界相較少且連續(xù)性較弱,擴(kuò)散后磁體表面形成core-shell結(jié)構(gòu)且深度達(dá)500μm,晶界相的連續(xù)性顯著增強(qiáng)。而稀土量為34wt.%的磁體,擴(kuò)散后晶界相的改善程度不及稀土量為30wt.%的磁體,因此矯頑力的增加量低于稀土量為30wt.%的磁體,但是晶界擴(kuò)散少于1.44 wt.% Tb時(shí),磁體的矯頑力高達(dá)28.12 kOe,是目前無(wú)重稀土晶界擴(kuò)散磁體矯頑力的最高值。這一工作對(duì)優(yōu)化不同牌號(hào)的燒結(jié)磁體的最佳擴(kuò)散效果、制備低重稀土高矯頑力燒結(jié)Nd-Fe-B磁體具有重要的指導(dǎo)意義。4.系統(tǒng)研究了晶界擴(kuò)散對(duì)不同稀土含量燒結(jié)Nd-Fe-B磁體使役性能的影響規(guī)律。高溫磁性能測(cè)量結(jié)果表明擴(kuò)散后磁體的矯頑力溫度系數(shù)有明顯的降低,溫度穩(wěn)定性得到改善。高溫條件下磁體的不可逆磁通損失隨稀土含量的增加而降低,晶界擴(kuò)散樣品的不可逆磁通損失顯著降低,極大地提高了磁體的使用溫度。擴(kuò)散樣品晶界處存在的大量氟化物,提高了磁體的電阻率。
[Abstract]:In order to meet the needs of the rare earth permanent magnets, such as electric vehicles, wind turbines, energy saving appliances and other emerging fields, the efficient utilization of rare earth resources, the improvement of the comprehensive magnetic properties of the magnets and the reduction of the heavy rare-earth use of high coercive magnets have become an important target for the study of the sintered Nd-Fe-B magnets. The influence of the key process and the content of rare earth on the properties of magnets was studied. The best diffusion process of heavy rare earth compounds DyF3 and TbF3 was determined. The best diffusion amount of the magnets with different rare earth content was optimized. The coercive force enhancement mechanism of the diffused magnets was clarified. The performance of the diffusion magnets was studied and the preparation of the diffusion magnets was studied. The sintered Nd-Fe-B magnets with high coercivity of low Re rare-earth and high re coercion have great significance for the large-scale manufacture and application of the electrophoretic deposition of grain boundary diffusion magnets. 1. the main research results are as follows: 1. by electrophoretic deposition, the uniform, smooth and controllable thickness of the sintered Nd-Fe-B magnets was successfully prepared. The best diffusion temperature and diffusion time of DyF3 are determined. By controlling the diffusion process parameters such as temperature and time, the coercive force of the magnet is greatly increased from 16.1 kOe to 22.8 kOe., with less than 1.2 wt.% Dy added to the heavy rare earth magnet, the increase of coercivity of the magnet is higher than 6.5 kOe, and the heavy rare earth is used. The efficiency is more than three times higher than the conventional powder metallurgy. The relationship between the Dy concentration in the diffusion sample and the distance of the magnet surface is precisely characterized. The analysis shows that the increase of the coercivity of the magnets is closely related to the concentration and distribution of the Dy elements. Through the analysis of the microstructure, the strengthening mechanism of the coercive force is clarified: after the high temperature diffusion, the Dy element is the main element. The magnetic field (Nd, Dy) 2Fe14B phase which has high magnetic anisotropy field in the main phase of the main phase is formed along the grain boundary, thus the coercive force of the magnet is greatly improved. In addition, the Nd element replaced by Dy is out of the grain boundary, and the phase transition of the grain boundary is more continuous and thicker, which makes the magnetic isolation between the adjacent main phase grains strengthen and advance. The influence of the thickness of DyF3 coating and the thickness of the magnets on the magnetic properties and microstructure of the sintered Nd-Fe-B magnets is systematically studied by improving the coercive force of the magnet.2.. The effect of the thickness of the coating and the thickness of the magnets on the magnetic properties and microstructure of the sintered Nd-Fe-B magnets is systematically studied. KOe is gradually increased to 24.04 kOe. by optimizing the thickness of the coating. The diffusion of the magnets can be significantly increased by 8 kOe in the non heavy rare earth magnets, and the coercivity of the magnets can be significantly increased by 8 kOe. The diffusion effect of the heavy rare earth elements is limited to the thickness of the magnets. The increase of thickness is gradually reduced. When the thickness of the magnet is 8.5 mm, the increase of coercive force is still 3.26 kOe, which is better than the best results reported at present. Thus, it is further confirmed that electrophoretic deposition is a method to accurately control the thickness of the coating and to prepare the thicker high coercive magnets with economic efficiency,.3. by electrophoretic deposition of TbF3. The effect of the rare earth content on the diffusion magnets at the grain boundary is studied systematically. The diffusion mechanism of heavy rare earth elements and the coercive force enhancement mechanism of the diffused magnets are clarified. The magnetic energy results show that the coercivity of the magnets with different rare earth content increases gradually with the increase of the thickness of the coating, and then tends to stabilize or decrease. The maximum coercivity increased for the initial magnet of 30wt.%, and the coercive force increased by 10.07 kOe when adding less than 0.81 wt.% Tb. The high quality utilization of heavy rare earth was realized. The microstructure analysis showed that the rare earth content was 30wt.%, the rare earth content was lower, the grain boundary phase was less and the continuity was weaker, and the core-shell junction formed after the diffusion of the magnets. With a depth of 500 mu m, the continuity of the grain boundary phase is significantly enhanced. The magnet with a rare earth content of 34wt.% is less than a magnet with a rare earth amount of 30wt.%, so the increase of coercive force is lower than that of a rare earth 30wt.%, but the coercivity of the magnetic field is less than 1.44 wt.% Tb, and the coercive force of the magnet is as high as 28.12 kOe. The highest value of coercive force of non heavy rare earth grain boundary diffusion magnets. This work has important guiding significance to optimize the best diffusion effect of different grades of sintered magnets and prepare Nd-Fe-B magnets with low weight rare earth and high coercive force sintering. The effect of grain boundary diffusion on the performance of Nd-Fe-B magnets with different rare earth content is studied. The measurement results of the temperature and magnetic properties show that the temperature coefficient of the coercive force of the magnets is obviously reduced and the temperature stability is improved. The irreversible flux loss of the magnet decreases with the increase of the rare earth content, and the irreversible flux loss of the grain boundary diffusion sample decreases significantly, which greatly improves the use temperature of the magnets. The presence of a large amount of fluoride at the grain boundary enhances the resistivity of the magnet.
【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類(lèi)號(hào)】：TM27

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