【作者】 夏华；

【导师】 严密；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2006， 硕士

【摘要】 纳米复相Nd₂Fe₁₄B/α-Fe型磁体是上世纪八十年代末发展起来的新型永磁材料,成本低廉。这种磁体是由Nd₂Fe₁₄B相和α-Fe相在纳米尺度内复合而成的。α-Fe相中原子磁矩的转动受Nd₂Fe₁₄B相的控制,因而这种磁体具有高剩磁和高磁能积的优点。但是,硬磁相Nd₂Fe₁₄B较低的居里温度限制了其在某些高温领域的应用。近年来,人们在烧结钕铁硼和传统单相粘结钕铁硼温度稳定性方面做了大量研究,但对有关纳米复相磁粉的温度稳定性研究相对不足。本文主要研究了合金成分对纳米复相Nd₂Fe₁₄B/α-Fe型永磁材料温度稳定性和磁性能的影响,并探讨了添加元素对磁体抗氧化性能的影响。 提高NdFeB工作温度的主要方法包括提高室温矫顽力和提高居里温度T_c。Zr元素能细化晶粒,显著提高室温矫顽力。故本文的研究都是在添加Zr的基础上进行的,首先研究了Nd含量对纳米复相Nd_xFe_93-xB₆Zr₁（x=9,9.5,10,10.5,11）合金磁性能和温度稳定性的影响。结果表明,Nd含量为10at%时,合金具有最高的剩磁（0.93T）、较高的矫顽力（780kA/m）,以及最好的温度稳定性:在180℃时的剩磁温度系数α为-0.154%/℃,矫顽力温度系数β为-0.39%/℃。在确定Nd含量为10at%的基础上,研究了B含量对纳米复相Nd₁₀Fe_93-xZr₁B_x（x=5,6,7,8）合金磁性能和温度稳定性的影响。结果表明,随着B含量的增加,合金剩磁和剩磁的温度稳定性变差;矫顽力和矫顽力的温度稳定性随着B含量的增加先变好后变差,在B含量为7at%时最佳。矫顽力为795kA/m（25℃）、矫顽力温度系数β为-0.37%/℃（180℃）。 在上一步工作的基础上,对添加元素Zr、Co、Dy和Ga进行了研究。实验结果表明:Zr含量为1at%时,有最好的综合性能,提高了剩磁和矫顽力,同时改善了磁体的温度稳定性;Co可有效的提高剩磁和降低α,使磁体的矫顽力略有下降,β变大;单独添加Dy或复合添加Dy和Co可以有效降低α和β,其中复合添加Dy和Co比单独添加Dy更为有效。0.5at%的Ga既可提高剩磁和矫顽力,同时有效降低α和β。 采用氧化增重法研究了Zr、Nb、Co、Dy元素对Nd₂Fe₁₄B/α-Fe型纳米复相磁体抗氧化性能的影响。实验结果表明,Nb、Zr可提高磁体抗氧化性能,在添更多还原

【Abstract】 The low cost nanocomposite Nd₂Fe₁₄B/α-Fe magnet is a new kind of magnetic material developed since the end of 1980s. This magnet consists of two phases, magnetically hard Nd₂Fe₁₄B and soft a-Fe. The rotation of magnetic moments in the a-Fe phase is controlled by Nd₂Fe₁₄B phase through exchange coupling effect, which gives this magnet high remanence and high-energy product. However the low curie temperature of Nd₂Fe₁₄B phase limits its application in the field requring high temperatures. In recent years, a lot of researches have been done on the thermal stability of sintered NdFeB permanent magnetic materials and conventional bonded NdFeB permanent magnetic materials. But there is little research on the thermal stability of nanocomposite Nd₂Fe₁₄B/α-Fe magnetic material. In the current investigation, the influence of alloy composition on the thermal stability and magnetic property of the nanocomposite Nd₂Fe₁₄B/α-Fe magnetic material are investigated. The effect of additional elements on inoxidizability of magnetic material is also discussed.The main methods to improve working temperature of NdFeB include to improve room temperature coercivity and to improve Curie temperature. Zr dopants can refine the grain and significantly improves the room temperature coercivity. So most of the alloys in this study contain Zr. Firstly, the effect of Nd on magnetic property and thermal stability in nanocomposite Nd_xFe_93.xB₆Zr₁ （x=9-11at %） was investigated. The results showed that Nd₁₀Fe₈₃B₆Zr₁ exhibited an acceptable comprehensive magnetic property (a B_r value of 0.932T and a H_Cj value of 780kA/m) and an outstanding thermal stability: -0.154%/℃ for the temperature coefficient of remanence a and -0.39%/℃ for the temperature coefficient of coercivity β at 180℃, respectively. After the Nd content was fixed at 10at%, the effect of B on magnetic property and thermal stability in nanocomposite Nd₁₀Fe_93-xZr₁B_x（x=5, 6, 7, 8） was investigated. The results showed that remanence and the thermal stability of remanence decreased with the increase in the B content. For the coercivity and thermal stability of coercivity, morderate B content was found. The coercivity andthermal stability of coercivity increased, and then decreased with the increase in the B content. NdioFes2B7Zri exhibited an optimal coercivity and thermal stability of coercivity, a //cj value of 795kA/m at 25 °C and a -0.37%/°C for the p at 180°C, respectively.Based on the above results, the effect of Zr, Co, Dy, and Ga was studied. The results showed that NdioFe83ZriB6 exhibited a comprehensive property. It possessed a better remanence and coercivity and improved thermal stability. The Co dopants can significantly improve romanence and reduce a, however the coercivity decreased and P increased with the increase in the Co content. The Dy addition and the combined Dy and Co addition can significantly reduce a and p. The combined Dy and Co had a better effect on thermal stability of magnetic material than Dy addition only. NdioFe82.5B6ZriGao.5 exhibited a higher remanence and coercivity and can significantly reduce a and p.The effect of Zr, Nb, Co, and Dy adition on inoxidizability in the nanocomposite Nd2Fei4B/a-Fe magnetic material was studied by thermo gravimetric analysis （TGA）. The results showed that Nb and Zr addition can improve inoxidizability of magnetic material. The combined Zr and Co additions can effectively improve anti-oxidation of samples. The Dy addition can slightly improve inoxidizability of magnetic material.更多还原