EQUILIBRIUM CRYSTALLINE PHASES IN ANNEALED (CO,FE)0.75B0.25 METALLIC GLASSES

Single-phase crystallites were observed by X-ray and electron diffraction in spinquenched (Co, Fe)0.75B0.25 metallic glasses that had been isothermally annealed near their crystallization temperatures. An orthorhombic cementite structure was observed in cobalt-based glasses and a body-centered tetragonal phase in the iron-based glasses corresponding to Co3B and Fe3B respectively. The Fe3B phase was found to be metastable, transforming into a mixture of α-iron and tetragonal Fe2B at temperatures just above the crystallization temperature of the glass. Crystalline areas in partially and completely crystalline Fe0.75B0.25 glasses contained grains of the order of 1.5 μm suitable for electron diffraction analysis. The apparent activation energy ΔE for crystallization was also determined from isothermal annealing experiments. The ΔE values were 61.9 and 65.2 kcal mol-1 for Fe0.75B0.25 and Co0.75B0.25 glasses respectively. Values of the Avrani exponent n were found to be 3.25 ± 0.18 in the iron-based glasses and 3.77 ± 0.30 for the cobalt-based glasses. © 1979.