Molecular Dynamics Study of Glass-Forming Ability of Zr-Based Metallic Glasses

Abstract

A new method to estimate the stability of supercooled liquid based on the temperature dependence of the free volume fraction, which is obtained by a molecular dynamics simulation with no empirical data was proposed. The molecular dynamics simulations for some Zr-based metallic glasses, Zr₅₅Cu₃₀Ni₅Al₁₀, Zr₆₇Ni₃₃ and Zr₆₇Cu₃₃ in Zr-Cu-Ni-Al system were performed. The features of the first peaks in calculated radial density functions well correspond to the experimental results by XRD and EXAFS spectroscope. The free volume fractions at 0 K in the quenched amorphous, F_quenched, and in “fully relaxed” supercooled liquid states, F_relaxed, are evaluated by the fitting of the temperature vs free-volume-fraction curve obtained by a molecular dynamics simulation. The calculated normalized free volume fraction N_free, defined as F_quenched⁄F_relaxed, shows similar tendency with other experimental T_rg. criterion. The temperature dependence of the free volume fraction in a supercooled liquid state governs the quenched free volume in the amorphous phase, which shows that the local structures in supercooled liquid or liquid phases are especially important for the glass formation.