Memory effect in enthalpy relaxation of two metal–alloy glasses

Aji, Daisman P. B.; Wen, Ping; Johari, G. P.

doi:10.1016/j.jnoncrysol.2007.02.059

Cited by 29 publications

(10 citation statements)

References 146 publications

(259 reference statements)

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“…There is no sub-T g peak when the sample was heated without ageing or when it was heated after ageing for relatively short periods of time in the calorimeter at a high temperature for the purpose of studying structural relaxation and memory effect. 65 Although our purpose is to discuss the JG-relaxation endotherm, we also consider the origin of the sub-T g peak at 418 K. This peak is not likely to arise from loss of internal stresses in the sample because loss of internal stresses produces an exotherm. 66 It is, however, conceivable that crystallites of a second phase could form during the ageing of the Pd 40 Ni 10 Cu 30 P 20 glass, and their melting produced a peak resembling the sub-T g peak.…”

Section: A the Sub-t G Peakmentioning

confidence: 99%

Kinetic-freezing and unfreezing of local-region fluctuations in a glass structure observed by heat capacity hysteresis

Aji

Johari

2015

The Journal of Chemical Physics

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Fluctuations confined to local regions in the structure of a glass are observed as the Johari-Goldstein (JG) relaxation. Properties of these regions and their atomic configuration are currently studied by relaxation techniques, by electron microscopy, and by high-energy X-ray scattering and extended x-ray absorption fine structure methods. One expects that these fluctuations (i) would kinetically freeze on cooling a glass, and the temperature coefficient of its enthalpy, dH/dT, would consequently show a gradual decrease with decrease in T, (ii) would kinetically unfreeze on heating the glass toward the glass-liquid transition temperature, Tg, and dH/dT would gradually increase, and (iii) there would be a thermal hysteresis indicating the time and temperature dependence of the enthalpy. Since no such features have been found, thermodynamic consequences of these fluctuations are debated. After searching for these features in glasses of different types, we found it in one of the most stable metal alloy glasses of composition Pd40Ni10Cu30P20. On cooling from its Tg, dH/dT decreased along a broad sigmoid-shape path as local-region fluctuations kinetically froze. On heating thereafter, dH/dT increased along a similar path as these fluctuations unfroze, and there is hysteresis in the cooling and heating paths, similar to that observed in the Tg-endotherm range. After eliminating other interpretations, we conclude that local-region fluctuations seen as the JG relaxation in the non-equilibrium state of a glass contribute to its entropy, and we suggest conditions under which such fluctuations may be observed.

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Section: A the Sub-t G Peakmentioning

confidence: 99%

Kinetic-freezing and unfreezing of local-region fluctuations in a glass structure observed by heat capacity hysteresis

Aji

Johari

2015

The Journal of Chemical Physics

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“…It is fraught with difficulty for modeling of glass aging and understanding its basic mechanisms due to the complex dynamics [3][4][5][6][7][8][9][10]. One peculiar phenomenon in glass aging is the memory effect, viz., during the relaxation toward its equilibrium state, a previously aged glass often shows a temporary neglect of its future (the equilibrium state) and a memory of its past, revealing history-dependent behaviors [11][12][13][14][15]. Memory effect is another manifestation of structural relaxation and ensures the proper description of the relaxation dynamics, thus, procures a deeper understanding of the complex glassy-state dynamics [2,15].…”

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confidence: 99%

Memory Effect Manifested by a Boson Peak in Metallic Glass

Luo

Bai

et al. 2016

Phys. Rev. Lett.

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We explore the correlation between boson peak and structural relaxation in a typical metallic glass. Consistent with enthalpy recovery, boson peak shows memory effect in an aging-and-scan procedure. Single-step isothermal aging produces monotonic decrease of enthalpy and boson peak intensity; for double-step isothermal aging, both enthalpy and boson peak intensity experience coincidently an incipient increase to a maximum and a subsequent decrease toward the equilibrium state. Our results indicate a direct link between slow structural relaxation and fast boson peak dynamics, which presents a profound understanding of the two dynamic behaviors in glass. *Corresponding author: pwen@iphy.ac.cn ** Corresponding author: whw@iphy.ac.cn 2 Metallic glasses own distinctive performances in mechanics and magnetics with respect to their crystalline counterparts. With a simple atomic packing, metallic glass offers an effective model system for the study of some controversial issues in glass science [1]. Due to its nonequilibrium nature, glass is continually relaxing toward a metastable equilibrium state, i.e., physical aging [2]. It is fraught with difficulty for modeling of glass aging and understanding its basic mechanisms due to the complex dynamics [3][4][5][6][7][8][9][10]. One peculiar phenomenon in glass aging is the memory effect, viz., during the relaxation toward its equilibrium state, a previously aged glass often shows a temporary neglect of its future (the equilibrium state) and a memory of its past, revealing history-dependent behaviors [11][12][13][14][15]. Memory effect is another manifestation of structural relaxation and ensures the proper description of the relaxation dynamics, thus, procures a deeper understanding of the complex glassy-state dynamics [2,15].Glass puzzles us not only with the localized complex atomic rearrangement arising from its nonequilibrium nature, but also with the peculiar low-frequency (terra is of paramount importance in discriminating between these theoretical models.In this letter, we trace the evolution of the boson heat capacity peak with the structural relaxation manifested by the relative enthalpy change. Upon single-step isothermal aging at a constant temperature, both enthalpy and boson peak intensity show a monotonic decrease toward the metastable equilibrium state. When the sample was firstly aged at a certain temperature and then stepped up to a higher one, an obvious nonmonotonic behavior emerges not only in enthalpy but also, intriguingly, in boson peak intensity, i.e., the memory effect is revealed. The memory effect manifested by boson peak behavior indicates clearly a direct link between the slow structural relaxation and the fast boson peak dynamics and brings a new perspective to the memory effect and the dynamics in glass.The Zr 50 Cu 40 Al 10 bulk metallic glass (BMG) was prepared by suck-casting from master alloy ingots to a copper mold cooled by water in an arc furnace. The pre-aged at a lower temperature before the second step aging, the endothermal...

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“…Curve labeled 0 is the plot obtained on its first heating. It shows no sub-T g endotherm [9,13], or a discernible exothermic minimum. A prominent hysteresis peak appears at 384 K before the almost equilibrium state of the compositionally different liquid is reached at 393 K. After curve 0 was obtained, the sample was immediately cooled from 393 to 293 K and then immediately heated back to 393 K at 20 K/min.…”

Section: Results and Data Analysismentioning

confidence: 99%

“…Nominally 15 mg of the sample was cut from this plate and used for studies by means of a Perkin-Elmer Pyris Diamond differential scanning calorimeter. As in previous studies [13,14,18,19], the instrument was calibrated by using pure indium and zinc as standards. To avoid errors resulting from a change in thermal contact, the samples were contained in crimp-sealed pans, which were heated and cooled inside the calorimeter.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…So, while the physical aging and memory effect of some bulk metal glasses [13,14] could be studied, those of the Ce 66 Al 10 Cu 20 Co 4 glass could not. To study the effect of incongruent crystallization on T g and on the T g -endotherm, we performed differential scanning calorimetry on both the cooling and heating paths while thermal cycling the samples of the Ce 66 Al 10 Cu 20 Co 4 glass continuously at q c = −q h .…”

Section: Introductionmentioning

confidence: 99%

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