Dilatometric measurements on metallic glass ribbons with a wide glass transition range

A special dilatometric device which avoids tensile stress to the specimen is used to examine structural relaxation, glass transition and crystallization of metallic glass ribbons of Al7.5Cu17.5Ni10Zr65 and Pd40Ni40P20. The relaxation kinetics can be well described either in the free volume model or by the Kohlrausch-Williams-Watts formula or by an activation energy spectrum, all indicating co-operative atomic rearrangements. The first model yields for the product of the critical free volume and overlap factor, initiating a structural relaxation event, values of 0.17 (Al7.5Cu17.5Ni10Zr65) and 0.14 (Pd40Ni40P20) of an atomic volume. The coefficient of thermal expansion (and its temperature dependence) is measured and found not to change with crystallization in the case of Al7.5Cu17.5Ni10Zr65, unlike that of Pd40Ni40P20.