Study On Phase Equilibrium Of La-Nd-Fe System And Properties Of Related Alloys

The phase diagram of the La-Nd-Fe ternary system is established through experiments.The solidification behavior of the ternary alloy with a Fe content of 65 at.%in this system and the magnetic properties and electromagnetic wave absorption properties of related alloys were studied.This paper provides a theoretical basis for the development of new high-abundance rare earth permanent magnets and other rare earth functional materials related to La.The main research contents are as follows:（1）The phase equilibrium relationship of La-Nd-Fe system at 873 K was determined by alloy method and diffusion triple technique.The existence of La Fe₂ and Nd Fe₂ phases was observed in the experiments.There was no ternary compound observed.The experiment accurately determined the solubility of each phase.The isothermal section of La-Nd-Fe ternary system determined by diffusion triple method at 873 K consists of 7single-phase regions(La Fe₂、Nd Fe₂、Nd₂Fe₁₇、Nd₅Fe₁₇、La、Nd、Fe),11 two-phase regions(La Fe₂+Fe,La+La Fe₂,La Fe₂+Nd₂Fe₁₇,La Fe₂+Nd,Nd+Nd₂Fe₁₇,La+Nd,Nd+Nd Fe₂,Nd₅Fe₁₇+Nd Fe₂,Nd₂Fe₁₇+Nd₅Fe₁₇,Nd₂Fe₁₇+Fe,Nd₂Fe₁₇+Nd Fe₂)and five three-phase regions(A1:La Fe₂+La+Nd,A2:Nd+Nd₂Fe₁₇+La Fe₂,A3:Nd₂Fe₁₇+Nd Fe₂+Nd,A4:Nd₅Fe₁₇+Nd Fe₂+Nd₂Fe₁₇,A5:Nd₂Fe₁₇+Fe+La Fe₂).（2）The solidification behavior of a ternary alloy with a Fe content of 65 at.%in the La-Nd-Fe system was studied,and the difficulty of forming La Fe₂ and Nd Fe₂ phases by alloy method was discussed.The as-cast solidification structure and phase transition reaction of La-Nd-Fe alloy were tested and analyzed by SEM/EDS and XRD.The type of phase transformation reaction was analyzed by the microstructure of the annealed alloy.Comprehensive experimental results found that the alloy method is difficult to generate La Fe₂ and Nd Fe₂ phases,and it is guessed that these two Laves phases are generated by the peritectoid reaction.（3）The magnetic properties and electromagnetic wave absorption properties of La_xNd_35-xFe₆₅ alloy micropowders,and the electromagnetic wave absorption properties of La₄Nd₃₁Fe₆₅/GO,La₁₉Nd₁₆Fe₆₅/carbonyl iron powder composites are studied in this paper.The experimental results show that the main phase of La_xNd_35-xFe₆₅ alloy is Nd₂Fe₁₇ or Nd₅Fe₁₇ phase,the second phase Nd will reduce the saturation magnetization and coercivity,while the second phase La can refine the grains and enhance the inter-grains exchange coupling to improve the magnetic properties.When x=4,the maximum saturation magnetization is 81.33emu/g.La₄Nd₃₁Fe₆₅ alloy has excellent electromagnetic wave absorption properties.Keeping the matching thickness of 1.8 mm unchanged,the effective bandwidth can reach 1.37 GHz,and the reflection loss is-20.55 d B（99%absorption rate）.Changing its thickness found that in the C-band,the peak value of the reflection loss is optimally-31.95 d B（99.9%absorption rate）,and the matching thickness is only 1.6 mm.GO composite is used to improve the wave absorbing properties of La₄Nd₃₁Fe₆₅alloy.When GO accounts for 5%of the total mass,the absorption strength of La₄Nd₃₁Fe₆₅/GO composite is enhanced,and the effective bandwidth is increased to 1.47GHz.When the thickness of the composite material is 1.2 mm,the effective bandwidth is widened to 2.14 GHz,and the peak of the reflection loss is-33.46 d B（99.9%absorption rate）.The reflection loss peak of La₁₉Nd₁₆Fe₆₅alloy is-28.37 d B（99.84%absorption rate）,but the effective bandwidth is only 0.39 GHz.Compounding with carbonyl iron powder increases its effective bandwidth.When the carbonyl iron powder accounts for 30%of the total mass,the effective bandwidth is widened from 0.39 GHz to 4.06 GHz,and the peak value of the reflection loss is increased from-28.37 dB to-31.10 dB.