MICROSTRUCTURAL CHANGE UPON ANNEALING FE-ZR-B ALLOYS WITH DIFFERENT BORON CONTENTS

Abstract

To clarify the reason for the change in effective permeability with increasing boron content before and after crystallization, we investigated the microstructure of Fe93-xZr7Bx (x = 2, 4, 6, 8) alloys annealed for 1 h in the temperature range 350-600-degrees-C, using transmission electron microscope. In low boron alloys (x = 2, 4), the amorphous phase showed indications of a typical interconnected pattern, exhibiting a spinodal-type decomposition. After crystallization, it changed to a mainly single b.c.c. structure with a homogeneous grain size distribution of about 20 nm, and the effective permeability had a high value of around 19000. In high boron alloys (x=6, 8), the microstructure after crystallization showed an inhomogeneous grain size distribution, and a low effective permeability. These results may be the result of the different phase separation pattern in the amorphous state.