Influence of microstructure on magnetic and mechanical behavior in amorphous and nanocrystalline Fe73.5Nb4.5Cr5Cu1B16 alloy

The amorphous Fe73.5Nb4.5Cr5Cu1B16 alloy is transformed to two-phase nanocrystalline material in the temperature range 450–550 °C. The changes in microstructure upon annealing are examined by X-ray diffraction and transmission electron microscopy. The resulting structure is composed of b.c.c.-Fe nanocrystalline grains with diameter of about 4–8 nm embedded in residual amorphous matrix. The correlations between microstructure and magnetic and mechanical properties in a series of heat treated amorphous and nanocrystalline samples are studied by VSM-magnetometry, hysteresis loop measurements and bending tests. It is shown that all obtained magnetic parameters depend strongly on a degree of crystallization in the investigated alloys. The degradation of soft magnetic properties with an increasing fraction of the nanocrystalline phase is supposed to be a consequence of the crystallization-induced changes in the residual amorphous matrix, which results in the weakening of the exchange coupling between nanocrystalline grains. The results of bending tests show that an embrittlement in investigated alloy occurs predominantly in the temperature region 200–400 °C, i.e., before nanocrystallization, being probably related to the atomic rearrangements in amorphous phase.