Evolution Of Microstructure And Magnetic Properties Of Nd₂Fe₁₄B/α-Fe Nanocomposite Permanent Magnets Deformed Hot Rolling

For Nd₂Fe₁₄B-based nanocomposite permanent magnets,it has a very high theoretical magnetic energy product and greatly reduces the use of rare earth elements,which has caused extensive research.But there is a big difference between the performance of the magnet pre-pared by the process and the magnet predicted by theory.The main reason is that it is difficult to obtain the hard magnetic phase texture under the condition of soft phase content>20%.Based on the research background In this paper,hot-rolling deformation experiments were performed on the bulk precursor at different temperatures.The magnetic energy product of the magnet obtained by this method is significantly higher than that of the magnet manufac-tured by the vacuum annealing process and the high-pressure heat treatment process when the precursor is the same.The mechanism analysis and research on the high performance of the magnet obtained by hot rolling deformation method is as follows:The vacuum annealing process is used to anneal the precursor at the temperature of450℃to 730℃,the phase change process of the precursor:at 450℃,the precursor is changed from amorphous began to transform intoα-Fe phase+Nd₂Fe₁₇phase;at 570℃,Nd₂Fe₁₄B phase began to appear,and the phase composition wasα-Fe phase+Nd₂Fe₁₄B phase+Nd₂Fe₁₇phase;At 730℃,Nd₂Fe₁₇phase disappears and is composed ofα-Fe phase and Nd₂Fe₁₄B phase.Then the magnet with the best hot-rolled deformation and the magnet with high-pressure heat treatment are compared.The hot-rolled magnet is an anisotropic magnet with a mag-netic anisotropy ratio is 1.64,and has（00L）crystallographic texture,the peak intensity ratio of（004）and（220）crystal planes is 221%,the high-voltage magnet is an isotropic magnet,the peak intensity ratio of（004）and（220）crystal planes is 105%,and the hard magnetic phase orientation is obviously weaker than that of hot-rolled magnets;hot-rolled magnet contains onlyα-Fe phase and Nd₂Fe₁₄B phase,and the phase content are 32.8%and 67.2%respectively.In the high-pressure heat-treated magnet containsα-Fe phase,Nd₂Fe₁₄B phase,Nd₂Fe₁₇phase and Nd₃Fe₂₉equivalent non-magnetic phase,and the phase content are 31.3%,47.9%,8.3%,10.7%;the maximum magnetic energy product obtained by the hot-rolled deformed magnet is 21.9 MGOe,Which is about 59%higher than the 13.8MGOe of the high-pressure heat-treated magnet,the coercivity is 5.3 k Oe,Which is about26%higher than the 4.2 k Oe of the high-voltage magnet,and the remanence of 10.6 k G is about 3%higher than the 10.2 k G of the high-voltage magnet.There are two reasons for the high performance of the hot rolling deformation process are analyzed:first,hot rolling deformation can achieve high-stress and large-strain ther-moplastic deformation of amorphous alloys,thereby promoting the oriented growth of hard magnetic phase nanocrystalline grains;secondly,hot rolling deformation is a rapid deforma-tion process,Which can avoid the formation interval of Nd₂Fe₁₇phase and Nd₃Fe₂₉equal non-magnetic phase,Remove the interference of the impurity phase,and make the exchange coupling effect of hard and soft good.