NANOCRYSTALLINE PHASE-FORMATION IN AMORPHOUS FE73.5CU1NB3SI13.5B9 SUBMITTED TO CONVENTIONAL ANNEALING AND JOULE HEATING

The influence of thermal treatment on the nanosized crystalline products developed from amorphous Fe735Cu1Nb3Si13.5B9 was studied by comparing the effects of different techniques such as isothermal annealing in a furnace and d.c. Joule heating. The microstructure of the produced samples was characterized using X-ray diffraction. A fitting procedure of the diffraction peaks of the resulting phase mixture was used to determine the contributions of the different phases (amorphous and nanocrystalline). A maximum crystalline fraction f(n) of about 60% was found in both conventionally and Joule annealed samples. The lattice parameter of the nanocrystalline phase was found to depend on f(n) independently of the annealing conditions. In conventionally annealed samples, the grain size increases with increasing f(n), ranging between 9 and 15 nm. However, a nearly constant value of about 11 nm was found in Joule heated samples. The initial magnetic permeability of samples submitted to Joule heating was found to be significantly higher than that of conventionally annealed samples. The effect of the type of heat treatment on nucleation and growth of the nanocrystalline phase is discussed.