放电等离子烧结和热变形Nd-Fe-B磁体的制备及性能研究

发布时间：2018-05-22 13:53

  本文选题：放电等离子烧结 + 热变形　； 参考：《南昌航空大学》2017年硕士论文

【摘要】：Nd-Fe-B基稀土永磁体以其优异的磁性能广泛应用于机电、航空航天、新能源汽车、信息及医疗等领域。热变形纳米晶Nd-Fe-B磁体的晶粒组织细小,晶间交换耦合作用较强,有利于提高磁体的温度稳定性。本文通过放电等离子烧结技术(SPS)制备了各向同性纳米晶Nd-Fe-B磁体,研究了PrCu低熔点合金添加对SPS磁体微观结构和磁性能的影响。基于SPS磁体,通过热变形技术成功制备出各向异性Nd-Fe-B磁体,利用晶界扩散(GBDP)对热变形磁体进行改性研究,获得了具有高矫顽力和高热稳定性的热变形纳米晶磁体。基于放电等离子烧结(SPS)技术,在700℃/50MPa/5min烧结条件下,制备出了具有优异磁性能的各向同性纳米晶Nd-Fe-B磁体,其矫顽力、剩磁和最大磁能积分别为:H_(ci)=1516kA/m、J_r=0.83T、(BH)_(max)=118kJ/m~3。由于放电等离子烧结所形成的暂态高温场,烧结磁体中存在呈层状分布的粗细晶区,细晶区由长宽比不同的晶粒所组成,而粗晶区多以等轴晶为主。研究了低熔点Pr-Cu合金的添加对烧结磁体性能的影响,确定了在添加15wt.%含量和650℃/50MPa/5min条件下所制备的烧结Nd-Fe-B磁体的矫顽力最高,矫顽力H_(ci)=1970kA/m。以放电等离子烧结磁体作为热变形磁体前驱体,通过热变形技术制备出了各向异性纳米晶Nd-Fe-B磁体。研究表明,变形过程中通过铜套的加入抑制了热变形磁体周边锯齿状的出现,增大了材料的利用率。热变形后,磁体磁滞回线的方形度有所改善,剩磁和最大磁能积均得到提高,热变形后磁体的矫顽力、剩磁和最大磁能积分别为:H_(ci)=752kA/m、J_r=1.27T、(BH)_(max)=272kJ/m~3。通过在热变形磁体中晶界扩散低熔点PrCu合金,制备出了矫顽力高达1945kA/m的热变形磁体,热变形磁体矫顽力的提高可能归因于晶界铁磁性元素含量的降低和晶界相分布均匀性的改善。500℃/3h晶界扩散条件下磁体的综合磁性能最为优异,磁体的矫顽力、剩磁和最大磁能积分别为H_(ci)=1515kA/m、J_r=1.22T、(BH)_(max)=262kJ/m~3。回复曲线研究表明,通过晶界扩散工艺,可将磁体的回复曲线张开程度大为降低至几乎闭合状态,磁体矫顽力也得到大幅提高,这归因于晶界扩散改性所带来的晶界相分布均匀性的改善。热稳定性方面,晶界扩散热变形磁体的矫顽力温度系数和剩磁温度系数分别为-0.59%%/K和-0.13%%/K,相比于初始热变形磁体,温度稳定性得到大幅改善,这表明通过晶界扩散可有效提高磁体的温度稳定性,促进其在高温领域的应用。矫顽力机制分析表明,热变形磁体的矫顽力由钉扎机制所控制。
[Abstract]:Nd-Fe-B based rare earth permanent magnets are widely used in the fields of electromechanical, aerospace, new energy vehicles, information and medical treatment due to their excellent magnetic properties. Thermal deformation nanocrystalline Nd-Fe-B magnets have fine grain structure and strong intergranular exchange coupling effect, which is helpful to improve the temperature stability of the magnets. In this paper, isotropic nanocrystalline Nd-Fe-B magnets were prepared by spark plasma sintering (SPS) technique. The effect of PrCu low melting point alloy addition on the microstructure and magnetic properties of SPS magnets was investigated. Based on SPS magnets, anisotropic Nd-Fe-B magnets were successfully prepared by hot deformation technique. Thermal deformation nanocrystalline magnets with high coercivity and high thermal stability were obtained by means of grain boundary diffusion (GBDP). Based on the spark plasma sintering (SPS) technique, isotropic nanocrystalline Nd-Fe-B magnets with excellent magnetic properties were prepared at 700 鈩，

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