Modification of the intergranular phase and its microstructure in NdFeB sintered magnets
Modification of the intergranular phase and its microstructure in NdFeB sintered magnets
We also provide neodymium magnet ceramic magnet, alnico magnet, SmCo magnet, rubber magnetand magnetic products. These products are widely used in micro-motor, motor, computer, instrument, meter, automobile, motorcycle, horologe, office equipment, toy, magnetic therapy device and daily life industries.
Xiamen Everbeen Magnet Electron Co.,Ltd. http://www.china-magnet.net
Add:Unit H, 4F Rihua Mansion, No. 8 Xinfeng 2nd road, Torch Hi-Tech Zone, Xiamen, China.
Tel:0086-592-5781916
Fax:0086-592-5123653
E-mail:info@china-magnet.net
Since its invention in 1983,sintered rare-earth NdFeB magnets have occupied a huge market in the past two decades ranging from voice coil motor for hard disc drive, magnetic resonance imaging devices to motors for automobile and power generator because of its high magnetic performance.The growing demands for NdFeB magnets require not only its superior magnetic properties but also additional properties such as corrosion resistance,thermal stability and mechanical properties etc.However,owing to the complicated structure of the magnets,the composition and microscopic structure of some phases in this material,especially the intergranular phase,are not clear at present,which is one of the keys point for improving the over-all properties of magnets.In this thesis,effects of intergranular additions of oxides and nitrides on magnetic properties and corrosion resistance of NdFeB magnets were investigated. Novel processing technique such as spark plasma sintering(SPS)was used to fabricate the anisotropic NdFeB magnets.Besides these,efforts were paid in understanding the relationship between chemical content and crystal structure of intergranular Nd-rich phase in NdFeB sintered magnets.
CaO,MgO,ZnO,Si3N4 and BN powders were added into the intergranular region of Nd15Dy1.2Fe77Al0.8B6 and Nd22Fe71B7 magnets.On the one hand,there is an obvious increase in coercivity and thermal stability of Nd22Fe71B7 by appropriate additions due to refinement of grain size.On the other hand,it is found that the oxides additives can improve the corrosion resistance of magnets in moisture,heat and electrochemical environment.Microstructural observation indicated that the volume fraction of intergranular phase with high oxygen content increased and that of intergranular phase with low oxygen content reduced with the increase of oxideadditive amount.The increase of intergranular phase with high oxygen content is a main reason for improved corrosion resistance because of its high stability.
We also provide neodymium magnet ceramic magnet, alnico magnet, SmCo magnet, rubber magnetand magnetic products. These products are widely used in micro-motor, motor, computer, instrument, meter, automobile, motorcycle, horologe, office equipment, toy, magnetic therapy device and daily life industries.
Based on a ternary NdFeB sintered magnet,relationship between composition and crystal structure of the Nd-rich intergranular phase was explored by transmission electron microscope(TEM)observations.It is found that the oxygen content decreases almost linearly with the increase of Nd content in the intergranular phase, and crystal structure of the Nd-rich phase clearly depends on its oxygen content.The following transformation route of Nd-rich phase is followed with increase of oxygen content:double close-packed hexagonal(dhcp);face-centered cubic(fcc); close-packed hexagonal(hcp).Therefore,it is possible that crystal structure of the Nd-rich phase can be understood if its oxygen content is known. Furthermore,as an advanced sintering technique,spark plasma sintering(SPS)was also used to prepare Nd15Dy1.2Fe77Al0.8B6 magnet.The effects of processing parameter to magnetic properties and microstructure were investigated.Grain size of NdFeB magnets prepared by SPS is fine and uniform,which is much smaller than that of conventionally sintered ones.Continuous thin film of the Nd-rich phase is formed along the grain boundary and the density of magnet is increased through tempering, which is the main reason to improving the magnetic properties.TEM observations indicate a conversion of crystal structure of the Nd-rich phase at triple junction site after tempering.
We also provide neodymium magnet ceramic magnet, alnico magnet, SmCo magnet, rubber magnetand magnetic products. These products are widely used in micro-motor, motor, computer, instrument, meter, automobile, motorcycle, horologe, office equipment, toy, magnetic therapy device and daily life industries.
Xiamen Everbeen Magnet Electron Co.,Ltd. http://www.china-magnet.net
Add:Unit H, 4F Rihua Mansion, No. 8 Xinfeng 2nd road, Torch Hi-Tech Zone, Xiamen, China.
Tel:0086-592-5781916
Fax:0086-592-5123653
E-mail:info@china-magnet.net
Tags: neodymium magnets NdFeB magnets Smco magnets