Intrinsic correlation between β-relaxation and spatial heterogeneity in a metallic glass (original) (raw)
Related papers
Real-time microscopy of the relaxation of a glass
Nature Physics
The understanding of the dynamics of a glass above its devitrification temperature remains incomplete. Here, we build a spatio-temporal map of the relaxation dynamics of a highly stable glass into its supercooled liquid using real-time atomic force microscopy imaging. This methodology enables direct visualization of the progression of the liquid phase and clarifies and quantifies the presence of localized fast mobility regions separated by giant length scales. Our data establish a clear correlation between dynamic length and time scales in glasses. This approach may also be applicable to unveil the microscopic structure and dynamics of other glass-forming systems with much shorter length and time scales, including liquid-cooled glasses.
New Microscopic Mechanism for Secondary Relaxation in Glasses
Physical Review Letters, 2009
The dynamics of simple molecular systems showing glassy properties has been explored by dielectric spectroscopy and nuclear quadrupole resonance (NQR) on the halogenomethanes CBr 2 Cl 2 and CBrCl 3 in their low-temperature monoclinic phases. The dielectric spectra display features which correspond to and -relaxation processes, commonly observed in canonical glass formers. NQR experiments, also performed in the ergodic monoclinic phase of CCl 4 , enable the determination of the microscopic mechanism underlying the dynamics in these simple model glasses: Molecules that are nonequivalent with respect to their molecular environment perform reorientational jumps at different time scales. Thus our findings reveal another mechanism that can give rise to typical -relaxation behavior, raising some doubt about the existence of a universal explanation of this phenomenon.
Transient Nature of Fast Relaxation in Metallic Glass
2022
Metallic glasses exhibit fast mechanical relaxations at temperatures well below the glass transition, one of which shows little variation with temperature known as nearly constant loss (NCL). Despite the important implications of this phenomenon to in aging and deformation, the origin of the relaxation is unclear. Through molecular dynamics simulations of a model metallic glass, Cu_64.5Zr_35.5, we implement dynamic mechanical analysis with system stress decomposed into atomic-level stresses to identify the group of atoms responsible for NCL. This work demonstrates that NCL relaxation is due to fully transient groups of atoms that become normal over picosecond timescales. They are spatially distributed throughout the glass and have no outstanding features, rather than defect-like as previously reported.
Structural origins of Johari-Goldstein relaxation in a metallic glass
Nature Communications, 2014
Johari-Goldstein or b relaxation, persisting down to glassy state from a supercooled liquid, is a universal phenomenon of glassy dynamics. Nevertheless, the underlying micromechanisms leading to the relaxation are still in debate despite great efforts devoted to this problem for decades. Here we report experimental evidence on the structural origins of Johari-Goldstein relaxation in an ultra-quenched metallic glass. The measured activation energy of the relaxation (B26 times of the product of gas constant and glass transition temperature) is consistent with the dynamic characteristics of Johari-Goldstein relaxation. Synchrotron X-ray investigations demonstrate that the relaxation originates from short-range collective rearrangements of large solvent atoms, which can be realized by local cooperative bonding switch. Our observations provide experimental insights into the atomic mechanisms of Johari-Goldstein relaxation and will be helpful in understanding the low-temperature dynamics and properties of metallic glasses.
The European Physical Journal E, 2021
We investigate the Johari-Goldstein (JG) b-relaxation process in a model metallic glass-forming (GF) material (Al90Sm10), previously studied extensively by both frequency-dependent mechanical measurements and simulation studies devoted to equilibrium properties, by molecular dynamics simulations based on validated and optimized interatomic potentials with the primary aim of better understanding the nature of this universal relaxation process from a dynamic heterogeneity (DH) perspective. The present relatively low temperature and long-time simulations reveal a direct correspondence between the JG b-relaxation time tJG and the lifetime of the mobile particle clusters tM, defined as in previous DH studies, a relationship dual to the corresponding previously observed relationship between the a-relaxation time ta and the lifetime of immobile particle clusters tIM. Moreover, we find that the average diffusion coefficient D nearly coincides with DAl, of the smaller atomic species (Al), and that the hopping time associated with D coincides with tJG to within numerical uncertainty, both trends being in accord with experimental studies indicating that the JG b-relaxation is dominated by the smaller atomic species and the observation of a direct relation between this relaxation process and rate of molecular diffusion in GF materials at low temperatures where the JG b-relaxation becomes the prevalent mode of structural relaxation. As an unanticipated aspect of our study, we find that Al90Sm10 exhibits fragile-to-strong (FS) glassformation, as found in measurements of many other metallic GF liquids, but this fact does not greatly alter the nature of DH in this material and the relation of DH to dynamical properties.
Journal of Non-Crystalline Solids, 2011
Because the theory of SER is still a work in progress, the phenomenon itself can be said to be the oldest unsolved problem in science, as it started with Kohlrausch in 1847. Many electrical and optical phenomena exhibit SER with probe relaxation I(t) ~ exp[-(t/τ) β ], with 0 < β < 1. Here τ is a materialsensitive parameter, useful for discussing chemical trends. The "shape" parameter β is dimensionless and plays the role of a non-equilibrium scaling exponent; its value, especially in glasses, is both practically useful and theoretically significant. The mathematical complexity of SER is such that rigorous derivations of this peculiar function were not achieved until the 1970's. The focus of much of the 1970's pioneering work was spatial relaxation of electronic charge, but SER is a universal phenomenon, and today atomic and molecular relaxation of glasses and deeply supercooled liquids provide the most reliable data. As the data base grew, the need for a quantitative theory increased; this need was finally met by the diffusion-totraps topological model, which yields a remarkably simple expression for 2 the shape parameter β, given by d*/(d* + 2). At first sight this expression appears to be identical to d/(d + 2), where d is the actual spatial dimensionality, as originally derived. The original model, however, failed to explain much of the data base (especially polymeric relaxation, as accurately measured through concordances between multiple probes). Here the theme of earlier reviews, based on the observation that in the presence of short-range forces only d* = d = 3 is the actual spatial dimensionality, while for mixed short-and long-range forces, d* = fd = d/2, is applied to four new spectacular examples, where it turns out that SER is useful not only for purposes of quality control, but also for defining what is meant by a glass in novel contexts. The examples are three relaxation experiments that used different probes on different materials: luminescence in isoelectronic crystalline Zn(Se,Te) alloys, fibrous relaxation in orthoterphenyl (OTP) and related glasses and supercooled melts up to 1.15T g , and relaxation of binary chalcogen melts probed by spin-polarized neutrons (T as high as 1.5T g ).
Dynamical and quasistatic structural relaxation paths in Pd40Ni40P20 glass
Applied Physics Letters, 2009
By sequential heat treatment of a Pd 40 Ni 40 P 20 metallic glass at temperatures and durations for which ␣-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are identified via ex situ ultrasonic measurements following each heat treatment. The dynamic relaxation paths are associated with hopping between nonequilibrium potential energy states of the glass, while the quasistatic relaxation path is associated with reversible -relaxation events toward quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy minima that exist within the inherent energy minimum of the glass, thereby supporting the concept of the sub-basin/metabasin organization of the potential-energy landscape.
Mechanical Relaxation of Metallic Glasses: An Overview of Experimental Data and Theoretical Models
Metals, 2015
Relaxation phenomena in glasses are a subject of utmost interest, as they are deeply connected with their structure and dynamics. From a theoretical point of view, mechanical relaxation allows one to get insight into the different atomic-scale processes taking place in the glassy state. Focusing on their possible applications, relaxation behavior influences the mechanical properties of metallic glasses. This paper reviews the present knowledge on mechanical relaxation of metallic glasses. The features of primary and secondary relaxations are reviewed. Experimental data in the time and frequency domain is presented, as well as the different models used to describe the measured relaxation spectra. Extended attention is paid to dynamic mechanical analysis, as it is the most important technique allowing one to access the mechanical relaxation behavior. Finally, the relevance of the relaxation behavior in the mechanical properties of metallic glasses is discussed.
Physical Review Letters, 2012
We use x-ray photon correlation spectroscopy to investigate the structural relaxation process in a metallic glass on the atomic length scale. We report evidence for a dynamical crossover between the supercooled liquid phase and the metastable glassy state, suggesting different origins of the relaxation process across the transition. Furthermore, using different cooling rates, we observe a complex hierarchy of dynamic processes characterized by distinct aging regimes. Strong analogies with the aging dynamics of soft glassy materials, such as gels and concentrated colloidal suspensions, point at stress relaxation as a universal mechanism driving the relaxation dynamics of out-of-equilibrium systems.