磁性固溶体系晶界相的熵强化模式及其作用于矫顽力的机理研究

The atoms to form grain boundary other than the atoms of magnetic phase are important for regulating the coercivity, mechanical properties, corrosion resistance and sintering shaping of permanent magnet. The grain boundary phase formed by them plays an important potential role to relieve the dependence on the medium and heavy rare-earths and to solve the "Brown Paradox" of permanent magnets. However, these elements in the alloy not only appear in the grain boundary but also are soluble in the grains, resulting in that they can not be used to illustrate clearly the mechanism of grain boundary on coercivity. Recently, we found that Ag element has the inhibitory effect on the solid-solution reaction, which mainly caused by regulating of Ag on entropy of the solid-solution reaction. With the characteristic of this kind of elements on solid-solution reaction in this complex magnetic solid-solution system, in this project the formation atoms of the grain boundary are limited to the grain boundary only. Then the grain boundary phase, with relatively controllable composition and with low melting point, is used to wrap the magnetic grains. So the mechanism of the grain boundary on the coercivity can be studied more clearly. This project is used to explain the effect of composition, structure and state of grain boundary phase on coercivity. It is expected to save medium and heavy rare earths and improve coercivity, to promote the research of permanent magnet's properties and to reduce cost of the whole permanent magnet industry.

除磁性主相成分以外的晶界形成元素对于调控永磁体的矫顽力、力学性能、抗腐蚀和烧结成型等具有重要的作用。它们形成的晶界相是缓解高矫顽力永磁对中、重稀土的依赖和解决永磁“布朗悖论”的重要潜在途径。但是这些元素在合金中不仅出现在晶界，同时也固溶于晶粒内部，导致一直不能很好地将晶界相作用于矫顽力的机理解释清楚。申请人前期发现Ag元素具有对固溶反应的抑制作用，其原因主要包括Ag对固溶反应熵的调节。利用多元磁性固溶体系中这类元素具有“关闭”固溶反应的特征，本项目研究将晶界形成原子仅仅限制于晶界，从而合成成分相对可控的、具有低熔点的晶界相来润湿和包裹住磁性晶粒，并以此更清晰地研究晶界相对矫顽力的作用机理。本项目用于解释晶界相的成分、结构、状态等对矫顽力的作用，有望节约中、重稀土和提高矫顽力，对于推动永磁性能研究的深入，以及促进整个永磁行业降低成本具有重要的意义。

除磁性主相成分以外的晶界形成元素对于调控永磁体的矫顽力、力学性能、抗腐蚀和烧结成型等具有重要的作用。这些元素在合金中不仅出现在晶界，同时也固溶于晶粒内部，导致一直不能很好地将晶界相作用于矫顽力的机理解释清楚。申请人前期通过热力学计算，发现Ag元素具有抑制固溶反应作用。本项目研究利用Ag等具有“关闭”固溶反应的特征，将晶界形成原子仅仅限制于晶界，从而更清晰地研究晶界相对矫顽力的作用机理。项目主要研究了Nd-Cu-Ag共晶体系在Nd-Fe-B晶界的扩散、偏聚行为，晶界相与磁性晶粒间的热应力情况，以及NdCu相在高温时的赝固态相变规律。本项目的研究工作纠正了Nd-Cu相图中关于NdCu在升温过程中产生多型性固态相变的错误认识；证实了项目立论中的“无磁性晶界相能够提高矫顽力，代替中重稀土使用”的猜想，为进一步低成本地增强磁体矫顽力指明了研究方向。成果对于节约利用我国的中重稀土资源具有重要的意义，项目探索的实验方法也有助于深化对金属相关材料的研究和开发。