Evolution of structural and dynamic heterogeneities and activation energy distribution of deformation units in metallic glass

Jiao, Wei; Wen, Ping; Peng, Hailong; Bai, H. Y.; Sun, Baoan; Wang, W. H.

doi:10.1063/1.4795522

Cited by 89 publications

(35 citation statements)

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“…The size, activation energy, intrinsic relaxation time and their distributions of flow units reflecting t he structural heterogeneity of a glass are quite different in various MGs [22]. The different structural heterogeneities cause the difference in behaviors of stress relaxation and can be manifested in different stress attenuation degrees.…”

Section: Science China Materialsmentioning

confidence: 99%

“…Then the distribution of p(E) can be calculated through Equation (4) as: We note that the amplitude and relaxation rate of stress relaxation have correlation with the test temperature. The higher relaxation temperature could activate more flow units and lead to faster and more complete relaxation [22]. linear relationship for all the MGs.…”

Section: Science China Materialsmentioning

confidence: 99%

“…An obvious crossover time τ c determined based on the intersection of the two power-law fittings represents the transformation of the two processes. The first fast power-law process corresponds to the s tochastic activation of the localized nano-scale flow units and consumes the applied energy quickly; and the second slow power-law process corresponds to s elf-organized c ooperative motion of the activated flow units [22]. In the fast process, a p ortion of the flow units with a shorter relaxation time and low activation energy are quickly activated, and then the residual flow units with higher activation energy are gradually activated with the time increasing [19].…”

Section: Science China Materialsmentioning

confidence: 99%

“…The nanoscale structural heterogeneity is found to relate closely to the dynamic heterogeneity (which can be reflected by the kinetic fragility m) of the metallic glass-forming liquids [17−21] and the viscoelasticity localized flow phenomenon in MGs activated by either external stress or temperature (corresponding to the deformation or initiation of the glass transition, respectively) [17−21]. The stress relaxation is found to be an effective method which can sensitively characterize and classify the microstructural heterogeneity and reveal the relaxation kinetics of the flow units of MGs below T g [19,22,23], and this method could be applied to accurately and readily classify the MGs based on their discrepancy in microstructural heterogeneity which closely related to the dynamic heterogeneity of MGs.In this letter, we apply an instantaneous activation-relaxation technique to investigate the stress relaxation behavior of a variety of metallic glasses. We show that in MGs, the different responses of viscosity to temperature in the liquid state could be reserved in the glass state and is manifested in different structural heterogeneities which can be reflected by using stress relaxation behaviors.…”

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Classification of metallic glasses based on structural and dynamical heterogeneities by stress relaxation

Bai

2015

Sci. China Mater.

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We show that the diverse dynamic responses of viscosity of the supercooled liquid near the glass transition temperature can be inherited to glassy state and expressed in the discrepancy of stress relaxation, demonstrating a structural heterogeneous basis for fragility. The metallic glasses with diverse dynamics and structural heterogeneities manifesting in different densities and distributions of flow units can be classified and characterized in terms of a parameter n, which can be readily determined through stress relaxation method and is comparable to the kinetic fragility m of the supercooled liquid. The parameter can classify diverse metallic glasses and also benefits for understanding the correlation between the structural and dynamical heterogeneities of the metallic glasses.Glassy state with unique and fascinating mechanical, dynamic and thermodynamic properties, which can be achieved by quenching from highly viscous liquid [1−4], is a universal property of condensed matter that lose its ability to flow. One of the most confusing issues in the glasses is that the viscosity ( η) of a glass-forming liquid can vary by several orders of magnitude in a narrow temperature range near the glass transition temperature (T g ) [5]. Based on the various responses of viscosity η to temperature, the kinetic fragility m is defined in terms of the shear viscosity η as [6−7]:The m, which is an index to characterize how fast the viscosity of glass-forming liquid increases with decreasing temperature while temperature (T) approaching T g , directly relates to the slowing down of the dynamics of the glass-forming liquids [6]. According to the concept of fragility, the glass-forming liquids can be roughly classified into two groups: strong and fragile liquids [6]. This classification attempts to construct a relation between the macroscopic transport property close to T g and the dynamics of glassy systems. After decades of researches, it has been found that the fragility can be traced back to dynamic and structural heterogeneities, topographic differences of the Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China * Corresponding author (email: hybai@iphy.ac.cn) energy landscape [7,8]. Some features and physical properties of the glass-forming liquids or the resultant glasses can also be correlated to the kinetic fragility, such as the temperature behavior of the shear elastic modulus [9], the specific heat jump at T g [10,11], Poisson's ratio [12], the glass-forming ability [13], and the vibrational properties of glasses far below T g [14]. Compared with other glasses such as polymer and oxide glasses, the supercooled liquid region of the metallic alloys is narrow and lack of thermal stability [15,16], the value of kinetic fragility m of the metallic glass-forming liquids is hard to be accurately detected, and only few compositions have the accurate values of fragility. Therefore, it is useful and important to find an accurate parameter to classify the metallic glasses far below T g .Recently, both comput...

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Section: Science China Materialsmentioning

confidence: 99%

Section: Science China Materialsmentioning

confidence: 99%

Section: Science China Materialsmentioning

confidence: 99%

mentioning

confidence: 99%

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Classification of metallic glasses based on structural and dynamical heterogeneities by stress relaxation

Bai

2015

Sci. China Mater.

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“…The measured stress drop Ds ¼ s onset À s end reflects the fraction of liquid-like zones 43,49 . From Fig.…”

Section: Disscussionmentioning

confidence: 99%

Evolution of hidden localized flow during glass-to-liquid transition in metallic glass

et al. 2014

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For glasses, the structural origin of their flow phenomena, such as elastic and plastic deformations especially the microscopic hidden flow before yield and glass-to-liquid transition (GLT), is unclear yet due to the lack of structural information. Here we investigate the evolution of the microscopic localized flow during GLT in a prototypical metallic glass combining with dynamical mechanical relaxations, temperature-dependent tensile experiments and stress relaxation spectra. We show that the unstable and high mobility nano-scale liquid-like regions acting as flow units persist in the glass and can be activated by either temperature or external stress. The activation of such flow units is initially reversible and correlated with b-relaxation. As the proportion of the flow units reaches a critical percolation value, a mechanical brittle-to-ductile transition or macroscopic GLT happens. A comprehensive picture on the hidden flow as well as its correlation with deformation maps and relaxation spectrum is proposed.

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

Liu

Madinehei

Pineda

et al. 2016

J Therm Anal Calorim

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6In this work, the mechanical relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass is explored by 7 mechanical spectroscopy. The temperature dependent loss modulus E''(T) shows the features of β 8 relaxation well below glass transition temperature Tg. This β relaxation can be well described in the 9 framework of anelastic theory by a thermal activated process with activation energy of 165 kJ mol -1 . 10Structural relaxation, also known as physical aging, has a large effect on the glass properties. The 11 activation energy spectrum of structural relaxation is characterized by differential scanning calorimetry 12 measuring the heat flow difference between as quenched and relaxed states. The obtained energy 13 spectrum is well described by a log-normal distribution with maximum probability activation energy of 14 176 kJ mol -1 . The obtained activation energy of structural relaxation is similar to that of β relaxation 15 observed from mechanical spectroscopy. Both values are also close to the Johari-Goldstein β relaxation 16 estimated by the empirical rule Eβ=26RTg. 17

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Evolution of structural and dynamic heterogeneities and activation energy distribution of deformation units in metallic glass

Cited by 89 publications

References 34 publications

Classification of metallic glasses based on structural and dynamical heterogeneities by stress relaxation

Classification of metallic glasses based on structural and dynamical heterogeneities by stress relaxation

Evolution of hidden localized flow during glass-to-liquid transition in metallic glass

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

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