Stabilization of Supercooled Liquid and Opening-up of Bulk Glassy Alloys.

Abstract

Bulk glassy alloys with thicknesses up to 75mm and a wide supercooled liquid region reaching 127K before crystallization were found to be fabricated in a number of multicomponent systems which satisfy the three empirical rules for the achievement of large glass-forming ability, i.e., (1) multicomponent alloy systems consisting of more than three constituent elements, (2) significantly different atomic size ratios above 12%, and (3) negative heats of mixing. The scientific significance of the rules has been proved based on a number of experimental data as well as on the kinetic theories of the nucleation and growth of a crystalline phase. By choosing appropriate compositions which satisfy the empirical rules, bulk glassy alloys in Mg-, lanthanide metal-, Zr-, Pd-, Fe- and Co-based systems were produced in cylindrical and sheet forms by various solidification processes. The bulk glassy alloys exhibit high tensile strength, good ductility, high elastic energy, high impact fracture energy and high corrosion resistance for Zr-based system and good soft magnetic properties for Fe-based system. Furthermore, their glassy alloys heated in the supercooled liquid region can be deformed into various shapes through viscous flow. The ideal Newtonian flow has been achieved in the supercooled liquid. The utilization of the ideal superplasticity enabled the achievement of an extremely large elongation exceeding 15000%. These excellent data allow us to expect that the bulk glassy alloys develop as a new type of engineering material.