Length scale effects on relaxations in metallic glasses

Bedorf, Dennis; Samwer, K.

doi:10.1016/j.jnoncrysol.2009.11.022

Cited by 24 publications

(20 citation statements)

References 22 publications

(26 reference statements)

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“…[10] With reduction of a dimension of bulk like material to a thin film, Bedorf et al argue that the string like processes are reduced or disappeared at a film thickness of ca. 30 nm [11]. This gives a first impression for a comparison with simulated length scales.…”

Section: Introductionmentioning

confidence: 75%

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Activation volume of microscopic processes in amorphous Pd77.5Cu6.0Si16.5 due to stress and temperature

Schwabe

Küchemann

Wagner

et al. 2011

Journal of Non-Crystalline Solids

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Section: Introductionmentioning

confidence: 75%

“…To calculate the activation length (the diameter of the activation volume), it was assumed, that the activation volume is spherical. [10,11].…”

Section: Sample Preparation and Measuring Setupmentioning

confidence: 99%

Activation volume of microscopic processes in amorphous Pd77.5Cu6.0Si16.5 due to stress and temperature

Schwabe

Küchemann

Wagner

et al. 2011

Journal of Non-Crystalline Solids

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“…Accordingly, a b-event is considered as a chain of atoms that moves back-andforth reversibly and cooperatively within the confinement of surrounding elastic matrix 14,45 . In light of this scenario, it is reasonable that strong and comparable magnitudes of interactions among all the constituting atoms are necessary for archiving a critical length for the string-like atomic configurations for the movements of b-events, whereas weak interactions (or large fluctuations) between certain atomic pairs would break the string-like configurations, making them less cooperative.…”

Section: Discussionmentioning

confidence: 99%

“…These findings are consistent with our observation that Cu promotes b-relaxations in Pd-Ni/Cu-P systems because of its strong interactions with Pd and P. In a Pd-Cu-Si MG, Bedorf and Samwer 45 studied the length-scale effects on relaxations and they found that by reducing the film thickness o30 nm, the b-relaxations are effectively suppressed. This result was explained because of the breakdown of the stress field surrounding the string-like excitation when free surfaces are reached and the pinning effects of free surface 45 . More recently, Casalini et al 52 used -SCH 3 to replace -OCH 3 group in poly(methyl methacrylate) and they found in dielectric spectra that the intensity of the b-relaxation is substantially reduced, as the result of the electronegativity of sulphur is much less than that of oxygen 52 .…”

Section: Discussionmentioning

confidence: 99%

Chemical influence on β-relaxations and the formation of molecule-like metallic glasses

et al. 2013

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Secondary (also known as Johari-Goldstein or b-) relaxations are an intrinsic feature of supercooled liquids and glasses. They are important in many respects but the underlying mechanisms are not well understood. A long-standing puzzle is why some glasses show b-relaxations as pronounced peaks, whereas others as unobvious excess wings. Here we demonstrate that these different behaviours are related to the fluctuations of chemical interactions by using prototypical systems of metallic glasses. A general rule is summarized: pronounced b-relaxations are associated with systems where all the atomic pairs have large similar negative values of enthalpy of mixing, whereas positive or significant fluctuations in enthalpy of mixing suppress b-relaxations. The emerging physical picture is that strong and comparable interactions among all the constituting atoms maintain string-like atomic configurations for the excitations of b-events and can be considered as the formation of molecule-like metallic glasses.

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“…It is of a dierent nature than primary relaxations, and the cooperative regions consist of IH to IHH atoms [124]. Experiments on colloidal glass formers conrm relaxation processes on the timescale of the -process [146] and also mechanical measurements on metallic glasses report consistently [9]. In the PEL, -relaxations are viewed as changes between inherent states, which are located within the same metabasin (cf.…”

Section: Microscopic Description Of Rearrangementsmentioning

confidence: 99%

Nonlinear response and avalanche behavior in metallic glasses

Riechers

Samwer

2017

Eur. Phys. J. Spec. Top.

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The response to dierent stress amplitudes at temperatures below the glass transition temperature is analyzed by mechanical oscillatory excitation of Pd 40 Ni 40 P 20 metallic glass samples in single cantilever bending geometry. The strain response of the material is well below the critical yield stress even for highest stress amplitudes, implying the expectation of a linear relation between stress and strain according to Hook's Law. However, a deviation from the linear behavior is evident, which is evaluated in terms of temperature dependence and inuence of the applied stress amplitude by two dierent approaches of evaluation. The nonlinear approach is based on a nonlinear expansion of the stress-strain-relation, assuming an intrinsic nonlinear character of the shear or elastic modulus. The degree of nonlinearity is extracted by a period-by-period Fourier-analysis and connected to nonlinear coecients, describing the intensity of nonlinearity at the fundamental and higher harmonic frequencies. While rather small stress amplitudes are connected to a linear response behavior, higher stress amplitudes result in nonlinear behavior, which is enhanced with increasing temperature. The characteristic timescale to adapt to a signicant change in stress amplitude in terms of a recovery timescale to a steady state value is connected to the structural relaxation time of the material, suggesting a connection between the observed nonlinearity and primary relaxation processes. The second approach of evaluation is termed the incremental analysis and relates the observed response behavior to avalanches, which occur due to the activation and correlation of local microstructural rearrangements consisting of a few tens of atoms. These rearrangements are termed as shear transformation zones and correspond to localized plastic events, which are superimposed on the linear response behavior of the material. Temperature and stress enhance the occurrence of intervals of monotonously increasing or decreasing strain. These are connected to avalanche behavior according to the power-law observed in the distributions of strain response. Despite the onset of nonlinearity observed in connection with the nonlinear analysis, the power-law behavior is extracted for all applied stress amplitudes, high and low, suggesting activated plastic events throughout the so called Hookean response regime. The intensity of strain response itself shows a direct relation to the strain rate of the experiment. Both approaches of evaluation are compared regarding common aspects and limits. Response phenomena connected to plastic events in the linear response regime are barely reported in literature even though their existence is implied. The incremental analysis yields experimental evidence supporting their occurrence. Moreover it reects the limits of the nonlinear approach, which neglects strain response on the small scale by the period-wise analysis of the data, resulting in an apparent linear strain response. Still, the nonlinear approach illustrates clearl...

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Length scale effects on relaxations in metallic glasses

Cited by 24 publications

References 22 publications

Activation volume of microscopic processes in amorphous Pd77.5Cu6.0Si16.5 due to stress and temperature

Activation volume of microscopic processes in amorphous Pd77.5Cu6.0Si16.5 due to stress and temperature

Chemical influence on β-relaxations and the formation of molecule-like metallic glasses

Nonlinear response and avalanche behavior in metallic glasses

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