The Research Of The Microstructure And Properties Of Novel Fe-based Amorphous And Nanocrystallized Alloys

Due to the unique properties like high permeability,low coercivity and so on,Finemettype amorphous/nanocrystalline alloys have been widely adopted in transformers,inductors and other electricity sectors.In this paper,Al and Mo are adopted as the micro alloying element to obtain better properties in Finemet-type alloys,amorphous samples with compositions of Fe73.5Si13.5B9-xAlxCu1Nb3（x=0,0.5,1,1.5,2 atom percent:at.%）and Fe_73.5Si_13.5B₉Cu₁Nb₃-xMox（x=0,1,2,3 atom percent:at.%）are prepared,then these samples are annealed at different temperatures for identical time,or identical temperature for different time.Soft magnetic properties are tested on these nanocrystalline samples,besides,their microstructures are analyzed.It is found that,Al-doped Finemet possesses wider temperature range between the two exothermic peaks on DSC result.The primary precipitation phase of Al-doped Finemet is α-（Fe,Si,Al）,which has lower magneto anisotropy,thus Al in Finemet enhances the permeability and decreases the coercivity.The initial permeability（at 1 kHz）of Fe73.5Si13.5B8.5Al0.5Cu1Nb3 annealed for 60 min is ³5000,and the coercivity is ¹ A/m,which is the best combination of soft magnetic properties among all the samples.Al-doped samples generally show better magnetic softness than Finemet,if treated at identical annealing temperature and time.Microstructure analysis with XRD and TEM show that the nanocrystal sizes in Al-doped Finemet（containing 0.5-1 at.% Al）are ¹0-20 nm,hence the Al-doped Finemet possess good magnetic softness.The temperature range between two crystallization peaks are reduced if Nb is substituted by Mo.The analysis results of soft magnetic properties show that,Mo substituting Nb led to the degraded magnetic softness.It is found that,the magnetic softness of 15 min annealed Fe73.5Si13.5B9Cu1Nb2Mo1 and Fe73.5Si13.5B9Cu1Nb1Mo2 are comparable to 60 min annealed Finemet.Longer annealing time leads to the decrease in permeability and increase in coercivity of these two samples.Fe73.5Si13.5B9Cu1Mo3 nanocrystallized sample shows severely degraded soft magnetic properties.The analysis of microstructure show that longer annealing time lead to an increase in crystal sizes in these two samples,meanwhile the crystal sizes in Finemet remain stable.Fe-B phase can be found in Fe73.5Si13.5B9Cu1Mo3 samples.These results show that Mo is a weaker diffusion barrier than Nb,and the inhibiting effect on nanocrystals growth is also weaker than Nb.The research of production technique of wide ribbon shows that cooling rate and heating temperature should adapt each other if wide ribbon with good quality is to be produced.The research find that under the condition of interrupted heating,30 m/s roller speed and 0.5 mm nozzle-roller distance,wide amorphous ribbons with good quality can be produced.