Bulk amorphous alloys with thicknesses up to 75 mm and a wide supercooled liquid region reaching 127 K before crystallization have been 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 % among the main constituent elements, and (3) negative heats of mixing among their elements. The scientific significance of the three empirical 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 three empirical rules, bulk amorphous 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 amorphous 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 bulk amorphous alloys heated in the supercooled liquid region can be deformed into various shapes by 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 amorphous alloys with a wide thickness range up to 75 mm develop as a new type of engineering material.
|ジャーナル||Materials Science Forum|
|出版ステータス||Published - 1998|
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