AN IN-SITU SYNCHROTRON STUDY OF NANOCRYSTALLIZATION IN (FE, CR)-SI-B(-CU-NB) ALLOYS

The nanocrystallization process in (Fe73.5-xCrx)Si13.5B9Cu1Nb3 (x = 0, 3 and 5) amorphous alloys has been studied by in-situ X-ray diffracti on, using a synchrotron radiation source. The nanocrystalline volume f raction and the mean grain size of the (Fe,Si) crystallites were estim ated from an intensity profile analysis of the main diffraction maximu m. Cr alloying lowers the crystalline fraction for the same annealing conditions. The mean size of the crystallites initially increases with increasing annealing time but the growth rate slows down and a satura tion value of about 12 nm is reached. The Si content of the (Fe, Si) p hase initially correlates with the concentration in the as-cast glassy alloy but a final value of about 21 at.% Si is reached. The transform ation kinetics are described by an Avrami exponent below unity, as usu ally found for Finemet alloys.