Quantitative crystallization and nano-grain size distribution studies of a FeCuNbSiB nanocrystalline alloy

摘要

Superior soft magnetic properties of nanocrystalline two-phase FeCuNbSiB alloy can only be attainable from a suitably nano-crystallized structure in the amorphous matrix. In this study a thermal-cycling-annealing process was adopted to anneal theamorphous specimens. The crystallization fraction of Fe{sub}73.5Cu{sub}1Nb{sub}3Si{sub}13.5B{sub}9 ribbons after different annealing was quantitatively measured by a DTA method through the integrated crystallization enthalpy from annealed samples versusthat of as-cast amorphous specimen. The crystallization fraction was estimated to be 70% as the specimen was annealed for 550°C×7.63 ks, the optimal annealing condition. Using this method, the crystallization quantity of the crystallized FeCuNbSiBamorphous alloy was accurately estimated and controlled during nano-crystallization processes.The nanostructure of the annealed flake were investigated by high resolution TEM. The population of grain size is dominant in the range of 3-9 and 3-11 nm, corresponding to isothermal annealing at 520 and 550°C, respectively, for 910 s. The average grainsize associated with the above two annealing conditions is estimated to be 7 and 8.5 nm, respectively. The portion of nanocrystals with grain size smaller than 10 nm is about 80% for the annealing at 520°C×910 s and 72% for the annealing at 550°C×910 s, respectively. However, there is only one α-Fe(Si) phase evidenced in the TEM diffraction patterns.