Relation of the thermodynamic parameter of disordering with the width of structure factor and defect concentration in a metallic glass

In this work, we show that above the glass transition there exists a strong unique interrelationship between the thermodynamic parameter of disorder of a metallic glass derived using its excess entropy, diffraction measure of disorder given by the width of the X-ray structure factor and defect concentration derived from shear modulus measurements. Below the glass transition, this relationship is more complicated and depends on both temperature and thermal prehistory.Comment: 6 pages, 2 Figure

Effect of the entropy on the shear viscosity of metallic glasses near the glass transition

We measured the shear viscosity of 14 metallic glasses differing with their mixing entropy $\Delta S_{mix}$. It is found that the viscosity at the glass transition temperature $T_g$ significantly increases with $\Delta S_{mix}$. Using calorimetric data, we calculated the excess entropy of all glasses $\Delta S$ with respect to their maternal crystalline states as a function of temperature. It is shown that the excess entropy $\Delta S$ both at room temperature and at $T_g$ \textit{decreases} with $\Delta S_{mix}$. It is concluded that glasses with "high mixing entropy" $\Delta S_{mix}$ correspond to MGs with \textit{low} excess entropy $\Delta S$. The origin of the increased shear viscosity at $T_g$ of glasses with high $\Delta S_{mix}$ is determined by their reduced excess entropy $\Delta S$.Comment: 12 pages, 4 Figure

Critical behavior of the fluctuation heat capacity near the glass transition of metallic glasses

The high-frequency shear modulus of five Zr-, Pd-, Cu-based conventional and two high-entropy bulk metallic glasses was measured in a wide temperature range up to the beginning of crystallization. Using these data and general thermodynamic relations, the "fluctuation" heat capacity $\Delta C_f$ determined by local structural fluctuations in the defect regions is introduced and calculated. It is found that $\Delta C_f$ temperature dependence for all metallic glasses has a large peak located slightly below or above the glass transition temperature but clearly lower than the crystallization onset temperature. The form of this peak resembles the characteristic $\lambda$-peak typical for order-disorder phase transitions. It is suggested that this $\Delta C_f$-peak reflects certain underlying critical phenomenon. The critical temperature $T_0$ (peak temperature) and corresponding critical index $\alpha$ are determined. Averaged over all seven metallic glasses under investigation in the initial and relaxed states, the critical index $\alpha=0.26$. The results obtained indicate that the fluctuations of thermal energy near the glass transition bear the marks of a continuous phase transition. However, the derived critical index is between those corresponding to a second-order phase transition ($\alpha\approx 0.1$) and a critical transition characterized by a tricritical point ($\alpha \approx 0.5$).Comment: 18 pages, 4 figure

Dynamics of Viscoplastic Deformation in Amorphous Solids

We propose a dynamical theory of low-temperature shear deformation in amorphous solids. Our analysis is based on molecular-dynamics simulations of a two-dimensional, two-component noncrystalline system. These numerical simulations reveal behavior typical of metallic glasses and other viscoplastic materials, specifically, reversible elastic deformation at small applied stresses, irreversible plastic deformation at larger stresses, a stress threshold above which unbounded plastic flow occurs, and a strong dependence of the state of the system on the history of past deformations. Microscopic observations suggest that a dynamically complete description of the macroscopic state of this deforming body requires specifying, in addition to stress and strain, certain average features of a population of two-state shear transformation zones. Our introduction of these new state variables into the constitutive equations for this system is an extension of earlier models of creep in metallic glasses. In the treatment presented here, we specialize to temperatures far below the glass transition, and postulate that irreversible motions are governed by local entropic fluctuations in the volumes of the transformation zones. In most respects, our theory is in good quantitative agreement with the rich variety of phenomena seen in the simulations.Comment: 16 pages, 9 figure