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

Abstract

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.Physical aging is not only of scientific interest [1,2] but also of great practical importance, as the performance stability of many technologically relevant amorphous materials such as oxide glasses, polymers and metallic glasses (MGs) depends on how aging affects their properties during the expected service life. For MGs in particular, aging can result in severe embrittlement [3] and bring about profound changes to fracture and fatigue properties [4]. Therefore, the ability to understand and characterize the micromechanisms of aging in MGs will play a central role in ensuring their success in a broad range of industrial and commercial applications.A key to understanding aging on the microscopic level is measuring the time scale on which the system rearranges its internal structure. These structural rearrangements are directly related to how fast microscopic density fluctuations in the system decay [5]. The physical quantity describing this is the density correlation function, which can be measured over a wide range of time scales using a variety of complimentary experimental techniques [6]. Additionally, it can be formally defined within the framework of statistical mechanics, allowing for detailed comparisons between experiment, theory [7] and simulation [8]. Access to the density correlation function is therefore fundamental for describing the dynamical behavior of glasses and achieving a consistent picture of structural relaxation on microscopic length scales.X-ray photon correlation spectroscopy (XPCS) has recently emerged as a novel technique for studying the microscopic dynamics of condensed matter [6,[9][10][11]. In XPCS, coherent beams of X-rays are scattered from a sample and the resulting fluctuations in intensity correlated over time. This enables measurement of the density correlation function on the atomic scale. of a unique stress-dominated dynamics characterized by subsequent aging regimes: a fast exponential growth for short waiting times, followed by a long, almost stationary regime. The latter has been observed also in network glasses [13] and is contrary to the steady slowing down of the dynamics during aging observed in macroscopic studies.Here, we investigate the atomic motion in a Pd 43 Cu 27 Ni 10 P 20 MG ribbon using XPCS and show that this system ages in a highly heterogeneous manner, consisting of quiescent periods of stationary dynamics interspersed with cooperative, avalanch...

Comparing the atomic and macroscopic aging dynamics in an amorphous and partially crystalline Zr44Ti11Ni10Cu10Be25bulk metallic glass

“…2(b)]. A similar stationary dynamics close to Tg was reported in recent XPCS studies on the Pd43Cu27Ni10P20 BMG 11 and also observed at low temperatures in hyper-quenched metallic glass ribbons subjected to long annealing times. 8,10 This crossover into a stationary dynamics regime and subsequent lack of aging in metallic glasses on the atomic length scale is a result of configurational changes to the glassy structure, which run independently of macroscopic density changes.…”

“…So far, we are unaware of any work that has thus far provided a direct link between Eshelby events and aging in metallic glasses, although recent studies have highlighted the important role played by atomic-level stresses. 11,13,32 The decrease in β near Tg reflects the system's close proximity to its equilibrium state (supercooled liquid), where the microscopic dynamics is indeed characterized by stretched exponential correlation functions, in accord with a heterogeneous dynamics scenario. [33][34][35] Upon cooling from the liquid, β increases smoothly and becomes constant, suggesting a continuous evolution from the supercooled liquid to the glassy state.…”

“…[5][6][7] In recent years, x-ray photon correlation spectroscopy (XPCS) has provided an unprecedented look into the aging dynamics of metallic glasses directly on the atomic length scale. [8][9][10][11][12][13] The existence of distinct structural rearrangements far below Tg, 8 compressed exponential relaxation functions 10 and intermittent aging dynamics 11 all suggest a complex microscopic picture of metallic glass aging, not reflected in measurements of bulk macroscopic quantities. [14][15][16] Here we investigate the microscopic dynamics in the Zr44Ti11Ni10Cu10Be25 (Vitreloy 1b) BMG.…”

Ultra-long-range dynamic correlations in a microscopic model for aging gels

“…Also, the potential connection to the observation of sudden collapse in many gels after an initial lag time [43] needs exploration. Whether the mechanisms discussed in the context of such low density materials can be extended to understand similar fast relaxations reported for denser aging glasses [44][45][46] also requires more investigations.…”

Coherent X-ray scattering reveals nature of dynamical transitions in nanoparticle–polymer suspensions

“…The nature of dynamics for our suspensions have been found to be stationary by measuring two time correlation functions (not shown here) at a given wave vector [43,44].…”