Correlation Between Dynamic Properties And Glass-forming Ability In Supercooled CuZr Alloys

The glass transition mechanism and glass-forming ability (GFA) have attractedintensive attention in the field of amorphous materials. The dynamic properties ofsupercooled alloys are closely related to GFA in glass transition. Some studies have foundthat glass-forming ability of CuZr alloys is related to the compositions. In this thesis, wehave quenched the liquid binary Cu（100-x）Zrx(30x70)alloys into glass states by usingmolecular dynamics simulations. We have calculated the viscosities and diffusioncoefficients of supercooled CuZr alloys, and have analyzed their temperature dependence.We have discussed the correlation between the dynamic properties and glass-formingability.In our work, we find that the best glass formers are actually more fragile close to theglass transition by studying systematically the temperature dependence of viscosity ofCu-Zr alloys liquids. A dynamic transition from low to high fragility have been observedwhen the glass-forming liquids are quenched into glass states, which shows morepronounced at some optimal compositions compared to other compositions. This transitionis associated with the more rapid decrease of the excess entropy of the liquids above andclose to the glass transition temperature. In order to verify the changes of the entropy offragile liquids, we have also calculated the thermodynamic quantities of thermalexpansivity,, and specific heat, CP, and the peaks are observed at the optimal compositionswhich is consistent with the entropy change.We have studied the variation of self-diffusion coefficients with temperature forCu-Zr alloys. According to the temperature dependence of viscosities and diffusioncoefficients, the Stokes-Einstein relation is examined. The results show that this relation isbroken in the low-temperature region near Tg, and the deviations are most pronounced atthe best glass-forming compositions, which indicates the high dynamic heterogeneity, andsuggests that high GFA relates to the dynamic heterogeneity in fragile systems. Finally, we have studied the relationship between heterogeneity and local structures by taking anexample of Cu50Zr50alloys.