Study On The Spinodal Decomposition Type Ribbon Magnets

Because of excellent processability,thermal stability and magnetic stability,Cu-Ni-Fe and Al-Ni-Co alloys have been extensively applied in instrumentation,electrical appliances,telecommunications,electro magnetic transmission device and aerospace devices which require high temperature stability.Actually,they have been the most indispensable permanent magnet materials in the present time.In this paper,we try to prepare the Cu-Ni-Fe and Al-Ni-Co ribbons by melt-spinning technology,and their magnetic properties are optimized by doping other elements and improving the annealing processes.Then the phase composition,microstructure and magnetic properties of ribbons are studied by using X-ray diffractometer,transmission electron microscope,scanning electron microscope,energy dispersive spectrometer and vibrating sample magnetometer.The results show that with the increase of Ni content,the grain size of Cu_80-xNi_xFe₂₀?x=5,10,20?ribbons is increased,and the grain morphology gradually changes from spherical particle to plum shaped equiaxed grain.In x=5 ribbons,the homogeneous microstructure with body-centered cubic Fe₇Ni₃-type phases embed in the face-centered cubic FeCu₄-type matrix phases which make the ribbons have the best magnetic properties of Hc=627.1 Oe,Br=1997.4 Gs,Bs=6797.2 Gs.After the Cu₇₅Ni₅Fe₂₀ ribbons are annealed at 435-835?,with the increase of annealing temperatures,the content of body centered cubic Fe₇Ni₃-type phases are gradually increased and the comprehensive magnetic properties of ribbons are decreased.With the decrease of Fe,Co,Ni and the increase of Cu,the spinodal decomposition phenomenon of Cu-Ni-Fe-Co ribbons are more obvious,the difference in composition between?₁ and?₂ phases are increased,the grain size is decreased,and the Cu-rich phases are formed at grain boundaries,subgrain boundaries and in the large grain interior.Annealing treatment at 830? for 30 min promotes the spinodal decomposition and improves the magnetic properties.After the as-spun Cu₅₈Ni₂Fe₁₀Co₃₀ ribbons are annealed at 435-835?,the?₁ phases gradually change from strip to sphere with increasing the annealing temperatures,and their magnetic properties are inversely proportional to the annealing temperatures.So the as-spun ribbons still behave the best magnetic properties of Hc=646.12 Oe,Br=1493.8 Gs,Bs=5253.4 Gs.Only a little spinodal decomposition occurres in the Al-Ni-Co-type as-spun ribbons,but the annealing treatment at 835oC for 10 min promotes the spinodal decomposition phenomenon.1 wt%B addition in Fe-7.5Al-13Ni-36Co-3Cu-0.5Nb-5Ti-1B can effectively reduce the grain size,but inhibit the occurrence of spinodal decomposition.However,adding 1 wt%Si can accelerate the spinodal decomposition.With the increasing of melt-spining speeds,both the content of grain boundary phases and the degree of order of main phases are improved in the added 1wt%Si ribbons,and the annealed ribbons melt-spun at 15 m/s present the best magnetic properties of Hc=1084.8 Oe,Br=7819.9 Gs,Bs=14133.0 Gs.