Study On The Effect Of Thermodynamic Undercooling On Solidification Characteristics Of Magnetic Alloy

In this paper,Nd₉Fe₇₂Ti₄C₂B₁₃ quenched ribbons at different melt superheat temperature were prepared by melt quenching,and then,then the Nd₉Fe₇₂Ti₄C₂B₁₃ nanocomposite permanent magnetic alloy was obtained by annealing.X-ray diffraction,The effect of the thermal undercooling caused by melt superheating treatment on the microstructure,the formation ability and the crystallization behavior of Nd₉Fe₇₂Ti₄C₂B₁₃ alloy by differential Scanning Calorimeter,Physics Property Measurement System were used to analyze.The XRD results showed that:when the melt overheating degree was 60K,the crystallinity of Nd₉Fe₇₂Ti₄C₂B₁₃ ribbons was 89.2%,and the microstructure of the alloy was composed of Nd₂Fe₁₄B,Fe₃B,?–Fe,Nd₂Fe₂₃B₃ and a small amount of amorphous phase.The melt superheat increased and the crystallinity decreased.When the melt superheat degree was130K,the microstructure of the quenched ribbons was completely amorphous.The results of DSC showed that the amorphous parameters?and?increased with the increase of melt superheat,which indicated that the melt superheat can increase the amorphous forming ability of Nd₉Fe₇₂Ti₄C₂B₁₃ alloy.After quenching,the quenched ribbons was gradually crystallized.When the melt superheat is 60K,the metastable phase 2:23:3 phase still exists,but its content decreases significantly with the increase of annealing temperature.The Nd₂Fe₂₃B₃ phase appeared at the low annealing temperature of 90K,110K and 130K,which leaded to the decrease of the magnetic properties.The crystallization was completed when the annealing temperature increased to 995K,and the microstructure of the Nd₉Fe₇₂Ti₄C₂B₁₃ quenched ribbons under the three kinds of superheat degree was composed of Nd₂Fe₁₄B,Fe₃B and?-Fe.Further increasing the annealing temperature,the grain size,especially the?-Fe grain growed rapidly,which led to the overall grain size was too large.In this paper,the XRD data of annealed ribons were analyzed by MAUD software.The phase content and grain size of Nd₉Fe₇₂Ti₄C₂B₁₃ quenched ribbons with different melt superheat degree at annealing temperature of 995K and 1000K were calculated.The results showed that:When the melt superheat exceeds 60K,with the increase of melt superheat,the grain size of the alloy increased and the phase content didn't change greatly.With the increase of annealing temperature,the grain size increased.With the annealing temperature increasing from 965K to 1000K,the magnetic properties of the Nd₉Fe₇₂Ti₄C₂B₁₃ quenched ribbons with different melt superheat increased by the increasing of annealing temperature,and the optimum magnetic properties were obtained at the annealing temperature of 995K,then declined.The magnetic properties of the samples were 90%,110K and 130K,respectively.The magnetic properties of the Nd₉Fe₇₂Ti₄C₂B₁₃ribbons were better than that of the T⁺=60K.The Nd₉Fe₇₂Ti₄C₂B₁₃ quenched ribbons with melt superheat degree of 90K had the best magnetic properties after 995K isothermal annealing:H_ci=515.76 k A·m^-1?B_r=0.72T??BH?_max=53.90 k J·m^-3.In this paper,we compared the structural and magnetic properties of Nd₉Fe₇₂Ti₄C₂B₁₃ribbons and Nd₉Fe₇₀Ti₄C₂B₁₅ ribbons at the same melt rapid quenching conditions.The effects of B content on microstructure and magnetic properties was researched.The results show that the microstructure of Nd₉Fe₇₂Ti₄C₂B₁₃ and Nd₉Fe₇₀Ti₄C₂B₁₅ribbons was different under different B content.When the superheat was 60K,the microstructure of Nd₉Fe₇₂Ti₄C₂B₁₃ ribbons was consists of Nd₂Fe₁₄B??-Fe and Fe₃B phases,but the microstructure of Nd₉Fe₇₀Ti₄C₂B₁₅ ribbons except containing these three phases,it was also contains a small amount of amorphous phase as well as metastable phase Nd₂Fe₂₃B₃ phase.After optimized annealing,The microstructures of the two alloys are composed of Nd₂Fe₁₄B??-Fe and Fe₃B.With the increase of B content,the grain size of the ribbons decreases,and the magnetic properties of the quenched Nd₉Fe₇₀Ti₄C₂B₁₅ ribbons are better than that of the Nd₉Fe₇₂Ti₄C₂B₁₃ uenched ribbons.