Mechanism Of Influence Of Element Addition On The Magnetic Properties Of Nano-crystalline Nd-Fe-B Magnets And Service Performance Evaluation

Nd-Fe-B permanent magnets are being applied into various areas such as wind turbines,wind power,energy-efficient appliances,and new energy vehicles,which greatly increases the demand of Nd-Fe-B permanent magnets.However the Curie temperature of Nd-Fe-B permanent magnets is relatively low ~ 585 K.Use of Nd-Fe-B permanent magnets at elevated temperatures is limited as their magnetic properties decay a lot.Improvement of thermal stability of the magnets can be achieved by increasing coercivity and Curie temperature via adding alloy elements.Therefore in the present work,Nd-Fe-B alloys have been prepared using fast quench method.The mechanism of influence of elements addition on the magnetic properties,thermal stability of the Nd-Fe-B permanent magnets have been investigated using advanced characterization techniques such as synchrotron radiation X ray absorption fine structure.The rule of Curie temperature change has been established via comparing information of atomic local structures of before and after adding elements.The performance has been evaluated for the Nd-Fe-B isotropic sintering magnets using spark plasma sintering.The influence of series of heavy rare earth elements on the magnetic properties,as well as the crystal structure and microstructure,of fast quenched Nd-Fe-B ribbons has been investigated.Also the effect of light rare earth element Ce on the magnetic properties has been systematically studied.Microstructure and constitutional fluctuation have been observed using high resolution transmission electron microscopy,scanning electron microscopy and energy dispersive spectra.Lattice parameters of the main phase with Ce have been obtained by transmission electron microscopy diffraction patterns and X-ray diffraction.The state of valence of Ce atoms has been determined using synchrotron radiation X-ray absorption fine structure.On the basis of Ce elements,Co and Cu have been added.Morphology and distribution of the rare earth rich phase has been characterized using high resolution transmission electron microscopy.Moreover,combining synchrotron radiation X-ray absorption fine structure and fitting results,the atomic distance between Fe atoms has been determined.The influence of atomic interaction on the Curie temperature has been studied.The thermal stability of Nd-Fe-B has been analyzed via measuring the temperature coefficients of remanence and coercivity.Sintering magnets have been prepared using spark plasma sintering technique.The effect of adding Ce,Co,Cu on the magnetic properties and thermal stability has been studied.The service performance has been assessed via high voltage accelerated corrosion and cyclic thermal shock experiment under the arbitrary working environment.In all,from the aspects of atomic local structure,crystal distortion and microstructural evolution,mechanism of the effect of adding alloy elements on the magnetic properties and thermal stability has been deeply investigated.Relationship between macro properties and atomic microstructure has been established.Theoretic and experimental guidance can be provided for constructing database of composition-microstructure-property-performance and designing cost-effective Nd-Fe-B permanent magnets.