Study On The Effects Of Y And Zr Doping On Magnetic Properties And Microstructure Of Bulk Amorphous NdFeB Alloy

Rare-earth magnetic materials are widely used as functional basic materials in motors and electromagnetic sensors.However,because rare earth is a national non-renewable resource strategic material,it is strictly controlled and its application is limited.Therefore,the development of a kind of bulk amorphous magnetic material with low rare earth content and high magnetic properties is widely concerned by scholars from various countries.For this reason,the bulk amorphous NdFeB was synthesized by the copper die casting process.The effects of the alloy composition,element doping and annealing heat treatment on the microstructure,amorphous formation ability and magnetic properties of the samples were studied.These improve the performance of bulk amorphous NdFeB alloys.Since Y element can improve the amorphous formation ability of the magnet,and Zr element can play a role in grain refinement,Y and Zr were selected for doping experiments.The main contents are as follows:?1?The effect of Y doping on microstructure and properties of NdFeB bulk alloysNd₇Fe₆₇B₂₂Mo₄ amorphous samples with different doping content of Y were prepared by copper mold casting method.The XRD pattern shows that the diffraction peaks of crystalline phases in the samples become lower with the increasing of doping amount of Y:from 0at%to 6at%.When doping amount of Y in the samples are 2at%and 4at%,the XRD patterns of tested samples are classical peaks,and samples separate out crystalline phases again when the doping amount of Y in the samples reaches 6at%.DSC analysis shows that?T_x increases first and then decreases.When the doping amount of Y reaches4at%,the?T_x reaches the maximum value of 66K,showing that the amorphous formation ability of the alloy increases first and then decreases;The conclusion of VSM shows that the coercive force of a 2 mm diameter Nd₇Fe₆₁B₂₂Mo₄Y₆ sample reaches a maximum when the doping amount of Y element is 6at.%:_iH_c is 0.027 kA/m.?2?Effect of annealing process on NdFeB bulk alloyThe Nd₇Fe₆₁B₂₂Mo₄Y₆ samples with 6at%Y and the largest coercive force were annealed and heat treated to reach the best magnetic properties.Annealing temperature are 720°C,740°C and 760°C,and time is 10 min.VSM studies show that as the annealing temperature of the sample alloy increases,the coercivity,remanence and maximum energy product of the sample increase first and then decrease.Annealed sample reaches the best properties:B_r=0.51T,_iH_c=1289 kA/m and?BH?_max=46.2 kJ/m³ after being annealed at 740?in10 minutes.According to XRD patterns,the annealed samples are composed of soft magnetic phases,?-Fe,Fe₃B,and hard magnetic phase Nd₂Fe₁₄B,however,the three-phase main diffraction peak intensity changes significantly showing that the amount of different phases in the samples is obviously affected by annealing.Combining VSM and XRD analysis,there is intensive exchange coupling between soft and hard phases in the sample among the process of annealing in 740?.So the sample annealed in 740?has the bestmagnetic properties.Because the grain size and phase composition of the soft magnetic phase and the hard magnetic phase in the sample do not match,the exchange coupling effect is weak and the magnetic properties of the sample are low either in temperature higher than 760?or in temperature lower than 720?.?3?The effect of Zr doping on microstructure and properties of NdFeB bulk alloysNd₅Fe₆₈B₂₃Mo₄ amorphous samples with different doping content of Zr were prepared by copper mold casting method.The XRD pattern shows that the diffraction peaks of crystalline phases in the samples become lower with the increasing of doping amount of Y:from 0.5at%to 2at%.When doping amount of Zr in the samples are 1at%and 1.5at%,the XRD patterns of tested samples are classical peaks,and samples separate out crystalline phases again when the doping amount of Zr in the samples reaches 2at%.DSC analysis shows that?T_x increases first and then decreases.When the doping amount of Zr reaches2at%,the?T_x reaches the maximum value of 92K,showing that the amorphous formation ability of the alloy increases first and then decreases;The conclusion of VSM shows that the coercive force of a 2 mm diameter Nd₅Fe₆₈B₂₃Mo₂Zr₂ sample reaches a maximum when the doping amount of Zr element is 2at.%:_iH_c is 7.4kA/m.