Concept of chemical short range order domain and the glass forming ability in multicomponent liquid

The concept of multicomponent chemical short-range order (MCSRO) domain is systematically developed by the experimental investigation of Zr-Ti-Cu-Ni-Al bulk metallic glass (BMG) and thermodynamic modeling and calculation. The existence of MCSRO domains in Zr-based BMG is verified by the observations of high-resolution transmission electron microscopy (HRTEM) images and the analysis of nano-beam electron diffraction patterns. The size of the nano-beam used in this work is 0.5 nm in diameter. Thermodynamic evaluation of the melt composed of multiple-MCSRO domains and glass-forming ability (GFA) based on the concept of MCSRO domains has also been conducted. It is indicated that the thermodynamic calculation of the GFA based on MCSRO model is consistent with the experimental data of crystallization activation energy and glass transition temperature for Ni-Zr and Zr-Cu binary alloys, and with supercooled liquid region (ΔT_x) for Zr-Ni-Al ternary alloy. The existence of MCSRO domain lowers the free energy of the melt (ΔG_MCSRO), resulting in a large undercooling and a larger energy barrier to the nucleation of a critical crystalline nucleus. Large ΔG_MCSRO, low melting point as well as co-existence of multiple MCSRO domains are valid criterion for the valuation of GFA.