The Research On Microstructure And Magnetic Properties Of Nd-La-Fe-B Magnet

Nd-Fe-B permanent magnet has wide application in many fields because of its excellent magnetic properties.The high price of the Pr and Nd element caused by their overuse,has triggered interest to replaced Nd and Pr with cheap and abundant RE elements,such as La and Ce.Nowadays,researchers have already prepared high performance RE-La-Ce-Fe-B and RE-Ce-Fe-B magnets successfully.However there are few study about La substitution,as La2Fe14B will decompose at high temperature.The effect of La on magnet remained unknown.In order to investigate the distribution of La and its effects on microstructure and magnetic properties,we used La to partly replace Nd in Nd-Fe-B magnet.We also prepared high performance RE-La-Ce-Fe-B magnet by optimizing the sintering and heat treatment process.Main results of the work are as follows:Decomposition will not occur in strip casting with La substitution(La/TRE =50wt.%),though La tends to go into grain boundary phase and will form many phases other than 2:14:1 phase,such as fcc-?-La,bcc-a-Fe and RE1.1Fe4B4.La will deteriorate the mobility and wettability of grain boundary phase,thus weakening the magnetic properties.With increasing La content,holes start to appear in the magnet,and the grain size grows.The grain boundary phase is inclined to agglomerate,and hcp-RE2O3 that only exist with high O content will appear.The fcc-REO will precipitate inside the main phase.These oxidates are harmful for the sintering process.La-Ce content is crucial to the optimum sintering and heat treatment temperature for binary main phase Nd-La-Ce-Fe-B magnet.The optimum sintering temperatures of 36wt.%and 45wt.%La-Ce magnets are 1030? and 1050?respectively,while the optimum 1st heat treatment temperatures are both 890 ?.The magnet with La-Ce substitution should employ a two-step heat treatment technology.