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Unusual fast secondary relaxation in metallic glass.

Wang Q, Zhang ST, Yang Y, Dong YD, Liu CT, Lu J - Nat Commun (2015)

Bottom Line: Structurally complicated glasses, such as molecular glasses, often exhibit multiple relaxation processes.By comparison, metallic glasses have a simple atomic structure with dense atomic packing, and their relaxation spectra were commonly found to be simpler than those of molecular glasses.Here we show the compelling evidence obtained across a wide range of temperatures and frequencies from a La-based metallic glass, which clearly shows two peaks of secondary relaxations (fast versus slow) in addition to the primary relaxation peak.

View Article: PubMed Central - PubMed

Affiliation: 1] Laboratory for Microstructures, Institute of Materials Science, Shanghai University, Shanghai 200072i, China [2] Center for Advanced Structural Materials, Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon Tong, Kowloon, Hong Kong.

ABSTRACT
The relaxation spectrum of glassy solids has long been used to probe their dynamic structural features and the fundamental deformation mechanisms. Structurally complicated glasses, such as molecular glasses, often exhibit multiple relaxation processes. By comparison, metallic glasses have a simple atomic structure with dense atomic packing, and their relaxation spectra were commonly found to be simpler than those of molecular glasses. Here we show the compelling evidence obtained across a wide range of temperatures and frequencies from a La-based metallic glass, which clearly shows two peaks of secondary relaxations (fast versus slow) in addition to the primary relaxation peak. The discovery of the unusual fast secondary relaxation unveils the complicated relaxation dynamics in metallic glasses and, more importantly, provides us the clues which help decode the structural features serving as the 'trigger' of inelasticity on mechanical agitations.

No MeSH data available.


Related in: MedlinePlus

The three-dimensional surface plot of the loss modulus E″ as a function of the testing temperature and frequency obtained from extensive DMA tests.Note that the experimental data (white dots) are superimposed on the surface plot.
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f2: The three-dimensional surface plot of the loss modulus E″ as a function of the testing temperature and frequency obtained from extensive DMA tests.Note that the experimental data (white dots) are superimposed on the surface plot.

Mentions: To obtain a holistic understanding of these secondary relaxation processes, the isothermal mechanical relaxation spectra E″(ω) of the La-based metallic glass were measured in the frequency window of 1 × 10−2≤f≤100 Hz by incrementally adjusting the testing temperature from 228 to 393 K at a step of 5 K. Figure 2 displays the three-dimensional surface plot of all the isothermal data so obtained from the DMA tests. Evidently, the mechanical relaxation behaviour of the alloy is dominated by the β′ relaxation at the testing temperature as low as 228 K, which is in agreement with the previous isochronal result shown in Fig. 1. As the testing temperature rises, the signal of the β-relaxation gradually emerges from the low-f end and ultimately prevails on the isothermal spectrum; by comparison, the signal of the β′-mode relaxation weakens with the increasing temperature, which merges into that of the β-relaxation in the form of ‘shoulder' and ‘excessive wings' successfully and finally becomes indistinguishable at the high temperature (Supplementary Fig. 3a–f). This behaviour is very similar to the temperature-driven transition of β to α relaxation, as reported in the literature2528.


Unusual fast secondary relaxation in metallic glass.

Wang Q, Zhang ST, Yang Y, Dong YD, Liu CT, Lu J - Nat Commun (2015)

The three-dimensional surface plot of the loss modulus E″ as a function of the testing temperature and frequency obtained from extensive DMA tests.Note that the experimental data (white dots) are superimposed on the surface plot.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525198&req=5

f2: The three-dimensional surface plot of the loss modulus E″ as a function of the testing temperature and frequency obtained from extensive DMA tests.Note that the experimental data (white dots) are superimposed on the surface plot.
Mentions: To obtain a holistic understanding of these secondary relaxation processes, the isothermal mechanical relaxation spectra E″(ω) of the La-based metallic glass were measured in the frequency window of 1 × 10−2≤f≤100 Hz by incrementally adjusting the testing temperature from 228 to 393 K at a step of 5 K. Figure 2 displays the three-dimensional surface plot of all the isothermal data so obtained from the DMA tests. Evidently, the mechanical relaxation behaviour of the alloy is dominated by the β′ relaxation at the testing temperature as low as 228 K, which is in agreement with the previous isochronal result shown in Fig. 1. As the testing temperature rises, the signal of the β-relaxation gradually emerges from the low-f end and ultimately prevails on the isothermal spectrum; by comparison, the signal of the β′-mode relaxation weakens with the increasing temperature, which merges into that of the β-relaxation in the form of ‘shoulder' and ‘excessive wings' successfully and finally becomes indistinguishable at the high temperature (Supplementary Fig. 3a–f). This behaviour is very similar to the temperature-driven transition of β to α relaxation, as reported in the literature2528.

Bottom Line: Structurally complicated glasses, such as molecular glasses, often exhibit multiple relaxation processes.By comparison, metallic glasses have a simple atomic structure with dense atomic packing, and their relaxation spectra were commonly found to be simpler than those of molecular glasses.Here we show the compelling evidence obtained across a wide range of temperatures and frequencies from a La-based metallic glass, which clearly shows two peaks of secondary relaxations (fast versus slow) in addition to the primary relaxation peak.

View Article: PubMed Central - PubMed

Affiliation: 1] Laboratory for Microstructures, Institute of Materials Science, Shanghai University, Shanghai 200072i, China [2] Center for Advanced Structural Materials, Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon Tong, Kowloon, Hong Kong.

ABSTRACT
The relaxation spectrum of glassy solids has long been used to probe their dynamic structural features and the fundamental deformation mechanisms. Structurally complicated glasses, such as molecular glasses, often exhibit multiple relaxation processes. By comparison, metallic glasses have a simple atomic structure with dense atomic packing, and their relaxation spectra were commonly found to be simpler than those of molecular glasses. Here we show the compelling evidence obtained across a wide range of temperatures and frequencies from a La-based metallic glass, which clearly shows two peaks of secondary relaxations (fast versus slow) in addition to the primary relaxation peak. The discovery of the unusual fast secondary relaxation unveils the complicated relaxation dynamics in metallic glasses and, more importantly, provides us the clues which help decode the structural features serving as the 'trigger' of inelasticity on mechanical agitations.

No MeSH data available.


Related in: MedlinePlus