Glassy and liquid metals, from microscopic to macroscopic dynamics

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Relaxation dynamics of metallic systems in the liquid/glass transition region

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Relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass explored by mechanical spectroscopy and calorimetry measurements

In this work, the mechanical relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass is explored by mechanical spectroscopy. The temperature-dependent loss modulus E″(T) shows the features of β relaxation well below glass transition temperature Tg. This β relaxation can be well described in the framework of anelastic theory by a thermal activated process with activation energy of 165 kJ mol−1. Structural relaxation, also known as physical aging, has a large effect on the glass properties. The activation energy spectrum of structural relaxation is characterized by differential scanning calorimetry measuring the heat flow difference between as-quenched and relaxed states. The obtained energy spectrum is well described by a lognormal distribution with maximum probability activation energy of 176 kJ mol−1. The obtained activation energy of structural relaxation is similar to that of β relaxation observed from mechanical spectroscopy. Both values are also close to the Johari–Goldstein β relaxation estimated by the empirical rule Eβ = 26RTg.Peer ReviewedPostprint (author's final draft

Phonon dispersion relation of metallic glasses

Experimental data on the phase sound speed of metallic glasses show anomalies in the terahertz range, reflecting an underlying complex behavior of their phonon dispersion spectrum not yet explained. We determine the phonon dispersion curve of metallic glasses by means of massive molecular dynamics simulations, allowing us to obtain the low-q region behavior with unprecedented detail. Results confirm that the sound speed is constant below the THz range, down to the macroscopic limit. On the contrary, a hardening of the sound speed, more notable in the transverse case, is found in the THz range. This behavior is modeled in terms of a relaxation model. The model gives quantitative agreement and allows us to determine a new threshold frequency ¿h, at the end of the boson-peak region. Above ¿h the shear modulus increases dramatically, reflecting the end of the amorphous-like acoustic propagation region characterized by the excess density of vibrational states.Peer ReviewedPostprint (author's final draft

Temporal evolution of the domain structure in a Poisson-Voronoi nucleation and growth transformation. Results for one and three dimensions

The distribution of spatial domain structures originated during one and three dimensional Poisson-Voronoi transformations are computed analytically extending the recently obtained re- sults for the two dimensional case. The presented method gives a full description of the developed microstructure and is valid for tessellations of any dimensionality. The temporal and spatial depen- dences of the domain structure are completely discriminated and separated, showing the existence of geometric configurations independent of time. A single computation of the probability distribution of these geometric configurations allows us to calculate the total free-boundary and size probabil- ity distributions at any desired time. The obtained results show full agreement with stochastic simulations and reproduce completely the previously existing partial results. A discussion about the potential applications of the method to the calculation of other geometrical properties and the characteristics of the final static structure leading to a gamma distribution of sizes is also presented

Modeling of the Sub-Tg Relaxation Spectrum of Pd42.5Ni7.5Cu30P20 Metallic Glass

In this work we study the mechanical relaxation spectrum of Pd42.5Ni7.5Cu30P20 metallic glass. The effect of aging on the relaxation behavior is analyzed by measuring the internal friction during consecutive heating runs. The mechanical relaxation of the wellannealed glass state is modeled by fitting susceptibility functions to the primary and secondary relaxations of the system. The model is able to reproduce the mechanical relaxation spectrum below the glass transition temperature (sub-Tg) in the frequency- temperature ranges relevant for the high temperature physical properties and forming ability of metallic glasses. The model reveals a relaxation spectrum composed by the overlapping of primary and secondary processes covering a wide domain of times but with a relatively narrow range of activation energies.Postprint (author's final draft

Tuning the memory dependence of vapour deposited metallic glasses

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Application of mechanically alloyed Mn-Al metallic particles to wastewater treatment: a comparative investigation of chemical and bacterial approaches to dye degradation in residual textile waters

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X-Ray Photon Correlation Spectroscopy Reveals Intermittent Aging Dynamics in a Metallic Glass

We use coherent X-rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. The rich diversity of this behavior reflects a complex energy landscape, giving rise to a unique type of glassy-state dynamics.Comment: 5 pages, 4 figure

XPCS on metallic glasses

It is only in recent years that the study of the microscopic dynamics of metallic glasses (MGs) has become possible thanks to the advance in X-ray photon correlation spectroscopy (XPCS). This is precisely the technique we used for the analysis of a La60N i15Al25 Lanthanum-based glass (LaMG) and a high-entropy LaCeY N iAl glass (LaHEMG). We are particularly interested in two parameters that describe their dynamics: the relaxation time τα and the shape parameter β , which describe the relaxation process at different temperatures. In this article we experimentally obtained these parameters from the characterisation of the intermediate scattering function obtained from the Xray Photon Correlation Spectroscopy (XPCS) technique at the European Synchrotron Radiation Facility (ESRF).2022/202