SHORT-RANGE ORDERING IN THE MELT AND ITS MANIFESTATION IN GLASSY FE-CO-B - INVESTIGATION BY POSITRON-ANNIHILATION LIFETIME

Six sets of ribbons of Fe64Co21B15 metallic glass obtained by rapid qu enching of the melt having different temperature and time history, sel ected with respect to the temperature-time evolution of melt viscosity , have been investigated by positron annihilation spectroscopy. The in terest has been focused on the correlation between the expected melt p recursor structure and the presence of ordered units (clusters, associ ations) in the amorphous matrix. Ribbons have been annealed for suitab le times at temperatures below and above the crystallization temperatu re. Such selective thermal treatment of the samples has enabled to acc entuate or anneal-out the effects of the presence of small ordered str uctural units as reflected by the positron annihilation lifetimes and positron affinities and by changes of electron structure obtained from electrical resistivity measurements. Fine structure of the amorphous matrix has been determined by analyzing the positron annihilation life time spectra with the use of a numerical Laplace transform method whic h provides continuous distributions of the position annihilation lifet imes. Differences in local ordering have been found for samples from m aster alloys with different melt histories. (C) 1997 Elsevier Science S.A.