Entropy of metallic glasses and the size effect on glass transition (original) (raw)
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Identifying the high entropy characteristic in La-based metallic glasses
Applied Physics Letters, 2021
High temperature deformation was probed in a La-based high entropy metallic glass with an evident slow β relaxation. The correlation between high 19 configurational entropy and high temperature deformation mechanism was analyzed. 20 On the one hand, by increasing the strain rate, the degree of deviation from Newtonian 21 behavior in high entropy metallic glasses is lower than that of conventional metallic 22 glasses, which is ascribed to the high configurational entropy. On the other hand, high 23 configurational entropy leads to a decrease of activation volume in high temperature 24 deformation of metallic glasses. Identifying the influence of high configurational 25 entropy on the deformation mechanism paves the way for further understanding of the 26 mechanical behavior of metallic glasses.
Physical Review Letters
Lacking the structural information of crystalline solids, the origin of the relaxation dynamics of metallic glasses is unclear. Here we report the evolution of stress relaxation of high-entropy metallic glasses with distinct-relaxation behavior. The fraction of liquid-like zones, determined at each temperature by the intensity of stress decay, is shown to be directly related to both the aging process and the spectrum of relaxation modes obtained by mechanical spectroscopy. The results shed new light on the intrinsic correlation between the static and dynamic mechanical response in high-entropy and conventional metallic glasses, pointing towards a sluggish diffusion high-entropy effect in the liquid dynamics.
Statistical Mechanics of Metallic Glasses and Liquids
Metallurgical and Materials Transactions A, 2010
It is difficult to formulate the statistical mechanical theory of liquids and glasses, because phonons, which are the basis for the statistical mechanics of lattice dynamics in crystals, are strongly scattered and have a very short lifetime in liquids and glasses. Instead computer simulation and the ''free-volume'' theory are most frequently used in explaining experimental results on metallic glasses. However, both of them suffer from serious problems, as discussed in this article. We propose an alternative approach based upon the dynamics of the atomic level stresses. We review recent progress with this approach and show that it is possible to calculate thermodynamic quantities, including the glass transition temperature and the kinetics of structural relaxation, by this approach.
Journal of Non-Crystalline Solids, 2013
With the aim of discussing recent conflicting views of configurational entropy in frozen-in systems, we begin this paper with a brief review of the history of the entropy concept. Whereas the 'conventional' view of entropy had been elaborated after long and heated debates, a recently proposed 'kinetic' view has denied the existence of residual entropy in amorphous systems. We thus examine the validity of the 'conventional' view and then propose a more complete picture of the glassy state from the complementary roles of two conflicting views. Above all, we analyze the consistency of the 'spatial sampling' method and the difference from the other two methods by using three simple models and thought experiments. Our first conclusion is that, as defined for non-equilibrium systems within the framework of thermodynamics, entropy remains an objective state variable for which an observation time needs not to be specified. The second is that, owing to its extensive nature, entropy is in fact strongly linked to the distribution in configuration and momentum space rather than to temporal integration. As an obvious consequence, the degree of structural disorder remains an essential issue in glass thermodynamics. The third is that the new concepts of magnitude and phase factor of entropy indicate that the 'conventional' view, according to which configurational entropy does not vanish in irreversibly frozen-in systems, is not only consistent with thermodynamic theory and available data, but also accounts for kinetic effects such as fluctuation phenomena. With the concept of phase factor of entropy, the number of phase factors visited during the observation time in the 'conventional' view turns to be almost equivalent to the entropy value defined by the 'kinetic' view. Finally, non-zero values of residual entropies measured by calorimetry based on the 'conventional' view are real and useful features that have a fundamental bearing on the physics and chemistry of real crystals and glasses. The 'kinetic' view is also a useful tool as well to understand the kinetic effects, such the rapid slowdown from liquids to glass and the glass transition. It is strongly hoped that a complete picture of the glassy state will be advanced further.
Determination of the entropy production during glass transition: Theory and experiment
Journal of Non-Crystalline Solids, 2020
A glass is a non-equilibrium thermodynamic state whose physical properties depend on time. In this paper, we address the issue of the determination of entropy production during glass transition. In a first part, for the first time we simulate the entropy production rate of a two-level system departed from equilibrium by cooling. We show that this system, which can simulate the basic thermodynamic behavior of a glass-former, obeys the Clausius theorem. This first theoretical part shows us the importance of the fictive temperature in order to determine the entropy production rate. In a second part, for the first time we determine experimentally, with a high degree of precision, the entropy production rate of a polymer-glass, the Poly(vinyl acetate), during cooling/heating at different rates, and also during annealing steps at different aging times. Although being on the order of few %, or less, of the configurational entropy involved in the glass formation, the positive entropy generated over different parts of the cycle is clearly determined. These new data may open new insights for an accurate thermodynamic treatment of the glass transition.
A glass transition scenario based on heterogeneities and entropy barriers
We propose a scenario for the glass transition based on the cooperative nature of nucleation processes and entropic effects. The main point is the relation between the off-equilibrium energy dissipation and nucleation processes in off-equilibrium supercooled liquids which leads to a natural definition of the complexity. From the absence of coarsening growth we can derive an entropy based fluctuation formula which relates the free energy dissipation rate in the glass with the nucleation rate of the largest cooperative regions. As by-product we obtain a new phenomenological relation between the largest relaxation time in the supercooled liquid phase and an effective temperature. This differs from the Adam-Gibbs relation in that predicts no divergence of the primary relaxation time at the Kauzmann temperature and the existence of a crossover from fragile to strong behavior.
A real-space description of the glass transition based on heterogeneities and entropy barriers
Eprint Arxiv Cond Mat 0102104, 2001
An alternative scenario for the glass transition based on the cooperative nature of nucleation processes and the role of entropic effects is presented. The new ingredient is to relate the dissipation during the relaxation process to the release of strain energy driven by the nucleation of progressively larger cooperative spatial regions. Using an equiprobability hypothesis for the transition between different metastable configurations, we obtain a relation between the free energy dissipation rate and the size of the largest cooperative regions. This leads to a new phenomenological relation between the largest relaxation time in the supercooled liquid phase and the effective temperature. This differs from the classical Adam-Gibbs relation in that predicts no divergence of the primary relaxation time at the Kauzmann temperature but a crossover from fragile to strong behavior.
Journal of Non-Crystalline Solids, 2006
The relationship between the total relaxation time at the glass transition s tot T g and Glass Forming Ability (GFA) of Bulk Metallic Glasses (BMG) has been discussed. Subsequently s tot T g is applied to estimate the GFA of Zr 52.5 Al 10 Ni 14.6 Cu 17.9 Ti 5 and Zr 57 Al 10 Ni 12.6 -Cu 15.4 Nb 5 BMGs. The result indicates that the GFA of the former is greater than that of the latter, which is also demonstrated by the widely accepted criteria of both supercooled liquid region DT x and reduced glass transition temperature T rg . That testifies the relaxation time of glass transition (s tot T g ) is feasible for depicting GFA of BMGs. As a criterion estimating GFA, s tot T g could be easily obtained in practice, and then the occurrence of this criterion will promote exploring new bulk glassy composition. In addition, when s tot T g and DT x are calculated, the characteristic temperatures are determined by a electrical resistivity method besides DSC method. The values obtained from electrical resistivity method agree well with those from DSC method, which proves that the electrical resistivity method is applicable for determining the characteristic temperatures of BMGs.