Quasi-periodic layer structure of die-upset NdFeB magnets

Isotropic magnets were prepared from melt-spun powders at different hot pressing temperatures from 550 to 700 oC,then upset into fully dense anisotropic magnets at the same die-upsetting temperature of 850 oC.Die-upset magnets had the characteristics of inhomogeneous microstructure,including well-aligned grains structure and nonaligned grains layers transverse to press direction,which was quasi-periodic layer structure with a total length of 5-15 m.Nonaligned grains layers were mainly made of large grains and had higher Nd content.To clearly understand the formation of layer structure,the microstructure of isotropic precursors with different hot pressing temperatures and their subsequent die-upset magnets was investigated.A new interpretation for the formation of layer structure was proposed in this paper: the layer structure was correlated to the original ribbon interface which was divided into three types based on the contact forms.Because of the incomplete contact of neighboring ribbons,concentration of stress occurred in the contacted points and the Nd-rich phase was squeezed into interspaces at high temperature under stress.Due to the release of interfacial energy and the fluidity of enough Nd-rich liquid phases,the nonaligned layers with large grains formed both in hot compaction and subsequent hot deformation process.The layer structure affected the magnetic properties of die-upset magnets.With increase of the hot pressing temperature,the nonaligned grains layers became thicker,and the magnetic performance of die-upset magnets decreased.It was necessary to reduce the thickness of large grains layers for the preparation of high-performance die-upset magnets.     

热变形温度对纳米晶Nd-Fe-B磁体性能的影响

为了研究纳米晶Nd-Fe-B磁体的热变形机理,在不同温度下对快淬粉进行热压热变形处理.通过分析不同温度下热变形过程中应力和磁体应变的变化,以及磁性能和SEM测试,研究了温度对热变形磁体性能和微观结构的影响,分析了热变形过程的热变形机理.结果表明,纳米晶磁体存在最佳的热压温度和热变形温度.当热压温度为550℃,热变形温度...     

Ga对HDDR磁粉热变形磁体磁性能和微观结构的影响

利用HDDR工艺制备出Nd32FebalBGax(x=0.0、0.2%、0.4%、0.6%、0.8%(质量分数))磁粉,并且对HDDR磁粉进行热压/热变形处理制备出全密度各向异性磁体。研究了热变形温度和Ga含量对Nd-Fe-B热变形磁体磁性能的影响,观测了不同Ga含量热变形磁体的微观结构,探讨了微量元素Ga的添加对用HDDR磁粉制备的热变形磁体微观结构和磁性能的影响机制。研究发现,Ga的添加能够明显减小热变形磁体的主相晶粒尺寸,改善磁体的微观织构,并可以同时提高热变形磁体的剩磁和矫顽力。当Ga含量为0.6%(质量分数)时,热变形磁体的磁能积达到最大值228.3kJ/m3。