Nd9Fe72Ti4C2B13合金过热熔体的过冷度及其对非晶形成能力和磁性能的影响

摘要

采用差热分析法研究了Nd9Fe72Ti4C2B13永磁合金形核过冷度ΔT-与其熔体过热度ΔT+的关系.在此基础上,通过对不同熔体过热度的薄带进行微观结构分析、热分析和磁性能测试,研究了熔体过热度对合金的非晶形成能力、组织演化和磁性能的影响.结果表明,合金的过冷度拐点对应的临界过热度为67 K.在8~67 K的过热度范围内,ΔT-随ΔT+的提高而急剧增大了58 K;而在67~146 K的过热度范围内,ΔT-随ΔT+而变化的幅度不大,其间的平均过冷度达到了181 K.ΔT+为60 K 的快淬薄带的微观组织由 Nd2Fe14B、Fe3B、α-Fe、Nd2Fe23B3相的纳米晶和少量非晶组成.随着ΔT+从60 K提高至130 K,快淬薄带中的Nd2Fe23B3、α-Fe和Fe3B纳米晶逐步消失,而非晶含量逐步增大,最终得到完全非晶.ΔT+为60 K 的薄带退火组织中存在有损于磁性的亚稳相Nd2Fe23B3,其磁性能低下;而ΔT+分别为90,110和130 K的薄带退火组织均由Nd2Fe14B、Fe3B、和α-Fe纳米晶组成,它们的磁性能较ΔT+为60 K的薄带的大幅提高.其中,ΔT+为90 K 的退火薄带的磁性能取得了最大值,其最佳值为H ci=521.57 kA/m,B r=0.75 T,(BH)max=66.31 kJ/m3,Mr/Ms=0.67.%The dependence of the nucleation undercooling degree ΔT-of Nd9Fe72Ti4C2B13permanent magnetic alloy on its melt overheating degree ΔT+was studied by differential thermal analysis.On this basis,the effects of the melt overheating degree on the glass formability,microstructure evolution and magnetic properties of the alloy were investigated by thermal analysis combining with microstructure analysis and magnetic properties test of the ribbons melt-spun at different melt overheating degree.The results show that the melt overheating degree threshold of the alloy corresponding to its turning points of the mean undercooling degree is found to be 67 K. The ΔT-increases sharply by 58 K with the ΔT+increasing during the range of 8-67 K,but it increases a little and the mean undercooling degree reaches 181 K when the ΔT+raises during 67-146 K.The microstructure of the ribbon melt-spun at ΔT+=60 K is composed with Nd2Fe14B,Fe3B,α-Fe,Nd2Fe23B3and a small amount of amorphous phases.And the amorphous content increases gradually while the Nd2Fe23B3,α-Fe and Fe3B nano-crystals gradually disappear as ΔT +raises from 60 to 130 K,and the completely amorphous structure is ob-tained when the ΔT+reaches 130 K.The metastable phase Nd2Fe23B3that is detrimental to magnetic properties exists in the annealed ribbon melt-spun at ΔT+=60 K,causing its magnetic properties to be very low.But only Nd2Fe14B,Fe3B and α-Fe nanocrystals are found in the annealed ribbons melt-spun respectively at ΔT+=90, 110 and 130 K,and the magnetic properties of these ribbons are substantially higher than those of the annealed ribbon melt-spun at ΔT+=60 K.Among these annealed ribbons,the magnetic properties of the ribbon melt-spun at ΔT+=90 K achieve maximum values,and its optimum magnetic properties are Hci=521.57 kA/m,Br=0.7 5 T,(BH)max=6 6.3 1 kJ/m3and Mr/Ms=0.6 7.