| 초록 |
More than a half-century, metallic glasses have been discovered in lots of compositional exploration with various developing methods. The wide discoveries have extracted mechanically and physically unusual properties from the glass-forming alloys comparing to conventional alloys. Especially, the meta-stable supercooled liquid state between glass transition and crystallization temperatures give a chance to use as a precursor to form ultrafine structured alloy by crystallization at the large undercooling condition (just above glass transition temperature) upon heat-treatment. The crystallization mechanism is a selectable factor determined by alloy composition, and crystallization kinetics such as, nucleation and growth rates can be accurately controlled by modulating the processing temperature in the supercooled liquid region. However, the minor elements such as Al, Si, B, etc., that have large negative mixing enthalpy with major alloying elements, commonly used to improve glass forming ability result in the complexation of alloy composition and formation of brittle compounds during crystallization, which limits their possible applicability for precursor materials. Here, we report a newly designed intermetallic metallic glass precursor with polymorphous crystallization mechanism considering for transformation into single-phase alloys with an ultrafine microstructure. The metallic glass precursor exhibits a wide supercooled liquid region of 43 K, suggesting a wide processing temperature for controlling crystallization kinetics based on quenched-in cluster model. For the crystallization behavior, we found significant temperature dependence of crystallization kinetics to determine final grain size of as-crystallized alloys, and the crystallization progress was directly observed using in-situ transmission electron microscopy. Furthermore, the metallic glass precursor can simplify fabrication processing for ultrafine-struvtured alloy using one-step heat-treatment technique, comparing to the classical expensive multi-processing system consisting of homogenization, severe plastic deformation and recrystallization at high temperature. Our approach and discovery on the metallic glass precursor for ultrafine structured alloys enabling commercial materials suggest a practicable alternative for industrial application of the metallic glasses. |
