Research On Preparation And Crystallization Of Fe-based Amorphous Alloys

Fe-based amorphous alloy is a sort of good soft-magnetic material with promising application prospect, which has excellent parameters (such as μc, Bs, Hc) above or close to the ones of best soft-magnetic crystalline materials. However the formability of Fe-base amorphous alloys is not so strong that cooling velocity of at least 10⁴K/S is necessary for achieving completely amorphous material. Now bulk amorphous ring of at most 3mm is prepared through adjusting composition and holding down the nucleation. Incapability of obtaining bulk amorphous alloy directly by liquid quenching is quite a bottleneck constraining the utility of Fe-based amorphous soft-magnetic material.People have developed FINEMET alloy whose typical component is Fe_73.5Cu₁Nb₃Si_13.5B₉.After annealed at 813K for a fixed time, the alloy has perfect soft-magnetic properties on account of ultramicro structure made up of nanophase. Success of FINEMET alloy enlighten us how to acquire superfine nanocrystal through annealing amorphous alloys. We carry on a series of experiments and researches in order to find similar phenomena in Fe-Al-Ga-Si-P-B amorphous alloys.Firstly, we prepare amorphous ribbons by spin quenching and find thermal parameters of amorphous specimens with different compositions by Differential Scanning Calorimeter and analyze the microstructure of as-cast amorphous samples by X-Ray Diffraction. Secondly, we chose the whole amorphous ribbon in as-cast condition and anneal them at different temperatures for 1500 seconds under vacuum + arc atmosphere. Microstructure and composition of as-anneal amorphous samples are analyzed through X-Ray Diffraction. The crystallization process and thermal stability are also discussed and evaluated.We conclude that a little addition of Cu (below 2 percents) has no effect on amorphous formability of Fe-Al-Ga-Si-P-B alloys. At the meantime, the effect of Cu addition is controlled by Cu-Al proportion. We hold that there exists strong interacting between the Cu-Al and Fe-Al atomic pairs, while Cu-Al proportion deviate from the critical amount, the intensive congestion of Cu-Al and complex fluctuation of free energy are initiated, so the contribution of Al to glass-forming ability is diminished. Because Cu can't dissolve in Fe-based alloys, Cu accumulates and becomenucleating site while heat-treating. In the course of crystallization Cu atomic group precipitated successively and brings down the growth of crystals. The addition of Cu heightens the crystalline temperature (Tx) and transfers the two-step crystallizing process of alloys to one-step process. It also makes glass-transform temperature (Tg) move to high-temperature region and even vanish.