Crystallization of amorphous Fe86Zr7-xNbxB6Cu1

Amorphous Fe86Zr7-xNbxB6Cu1 alloys with x=0-5 were prepared by rapid quenching from the melt. The crystallization was investigated by means of X-ray diffraction and DSC measurements. In the first step of the crystallization nanocrystalline b.c.c. Fe solid solution is formed. The exchange of Zr with Nb leads to a reduction of the crystallization temperature and to smaller grain size from 10 nm (x=0) to 8 nm (x=5). In situ observation by means of high temperature X-ray diffraction shows crystallization after a temperature dependent incubation time. During isothermal annealing the mean crystallite size D increases with asymptotic growth behaviour. Annealing at different temperatures between 500 degrees C and 650 degrees C does not influence the mean grain size of the formed b.c.c. Fe crystals. The kinetics of crystallization of amorphous Fe-Zr-B and Fe-Si-B-Cu-Nb alloys differs from that of ordinary metallic glasses. The changes of nucleation rate and stability of the surrounding amorphous phase of the growing b.c.c. Fe phase plays an important role for the formation of a nanocrystalline microstructure.