热变形钕铁硼磁体晶界扩散的各向异性研究

It is a significant pathway to develop grain boundary (GB) diffusion technology to increase the coercivity of Nd2Fe14B permanent magnets. The grain boundary phases (GBP) which is considered as the channel and intermediary play a crucial role in the grain boundary diffusion process. Because of the stacked structure of regular plate-like shaped grains in hot deformed Nd2Fe14B magnets, the GB diffusion channel is remarkably anisotropic along the directions in the basal and side planes of the plate-like shaped Nd2Fe14B grains. In this project, the diffusion materials are introduced by the dual-alloy process firstly and followed by hot press to prepare the precursors. And then the precursors are hot deformed along the directions which are parallel and perpendicular to the hot press direction, respectively. In these magnets, the structures that the basal planes of the plate-like shaped Nd2Fe14B grains are parallel and perpendicular to the layers of the diffusion materials are formed. Meanwhile, the effects of differences of the diffusion channels on the diffusion anisotropy are studied in detail. The effect of the composition of the diffusion materials on the magnetic properties will be also investigated. In addition, the microstructures of the GBs and the characteristics of GBPs of the plate-like shaped Nd2Fe14B grains are systematically analyzed to investigate the GB diffusion anisotropic mechanism. The analysis of the magnetization behaviors and the corresponding macro-/micro-magnetic domain structure and variation are carried out to explain the domain wall pinning and magnetic isolation in the GB diffused hot deformation magnets. The diffusion technology that the diffusion quantity is controllable and the diffusion materials are high efficiently utilized will be explored to achieve the approach of coercivity enhancement in hot deformed Nd2Fe14B magnets.

发展晶界扩散技术是提高钕铁硼永磁体矫顽力的重要途径，作为晶界扩散的通道和媒介，晶界相起着至关重要的作用。热变形钕铁硼磁体具有相对规则的片状晶粒有序层状堆叠结构，片状晶基平面和侧面方向的晶界扩散通道各向异性显著。本项目采用双合金工艺引入扩散物，沿平行和垂直于热压毛坯压力方向进行热变形，形成片状晶基平面与扩散合金层平行和垂直的结构，并研究扩散通道差异对扩散各向异性的影响。掌握扩散物组分对磁性能的影响规律，分析片状晶不同晶界的显微组织结构及晶界相特征，研究晶界扩散各向异性机制。通过磁体磁化与反磁化行为及其对应的宏观及微观磁畴结构以及演变的分析，阐述晶界扩散热变形磁体磁畴壁钉扎及磁隔离作用。探索扩散量可控和扩散物高效利用的技术，达到提高热变形钕铁硼磁体矫顽力的目的。

在稀土永磁材料中，为了获得较高的矫顽力，通常采用晶界扩散重稀土元素或低共晶点合金。而热变形钕铁硼永磁体晶粒细小，具有亚微米晶结构，理论上能够获得较高的矫顽力。但热变形磁体的矫顽力相对于传统具有微米晶的烧结磁体无明显优势。.因此为了提高热变形磁体的矫顽力，最常用的技术是晶界扩散低共晶点合金。现阶段的晶界扩散为不可控晶界扩散，导致非磁性相在磁体内含量较多，剩磁和磁能积降低显著。本研究的目的主要在于研究热变形钕铁硼磁体中的晶界扩散机制，从而调控晶界相在磁体内的择优分布，探索适合热变形钕铁硼磁体矫顽力提升技术，为今后重稀土在热变形钕铁硼磁体中的高质化利用打下坚实的基础。.通过项目的实施，研究了在热变形钕铁硼磁体中，低共晶点合金晶界扩散存在着各向异性，各向异性主要由热变形磁体宏观与微观结构共同作用导致。宏观上，快淬条带周期性层状堆叠结构，微观上存在着片状纳米晶以及晶界相的各向异性分布的结构。采用垂直变形的方式，进一步验证快淬带周期性堆叠是晶界扩散各向异性一个重要因素。采用压力诱导晶界扩散的方式可以调控晶界扩散磁体中液相的择优分布，研究表明磁畴结构与液相含量紧密联系。当液相含量增加时，迷宫状磁畴结构变为细小且不连续的磁畴。对磁体矫顽力机制进行线性拟合发现，磁畴壁钉扎在纳米晶钕铁硼磁体矫顽力机制中起主导作用。在以上研究基础上，开展了热变形钕铁硼磁体中重稀土元素高质化利用的探索工作。研究表明，重稀土元素的晶界扩散可在不显著降低磁体性能的基础上，显著提高磁体矫顽力，为今后开展重稀土高质化利用指明了一条可行的研究方向。.通过项目的实施，共培养硕士生3名，博士生2名，发表12篇SCI学术论文。