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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 emergence of two secondary relaxations in the La-based metallic glass on the isochronal dynamical mechanical spectrum.The temperature dependence of loss modulus, E″ and storage modulus, E′, was obtained at the testing frequency of 1 Hz and heating rate of 3 K min−1. The red and green regions represent the Cole–Cole (C–C) fitting of the fast β′ and slow β relaxation, respectively, while the yellow region represents the H–N fitting of the α-relaxation.
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f1: The emergence of two secondary relaxations in the La-based metallic glass on the isochronal dynamical mechanical spectrum.The temperature dependence of loss modulus, E″ and storage modulus, E′, was obtained at the testing frequency of 1 Hz and heating rate of 3 K min−1. The red and green regions represent the Cole–Cole (C–C) fitting of the fast β′ and slow β relaxation, respectively, while the yellow region represents the H–N fitting of the α-relaxation.

Mentions: For this study, we chose a La-based bulk metallic glass as the model material, which has the chemical composition of La56.16Ce14.04Ni19.8Al10 (in atomic %). As seen in the later text and Supplementary Information, this La-based metallic glass has an excellent thermal stability and pronounced β relaxation. The amorphous nature of the La-based alloy is confirmed by means of X-ray diffraction as well as differential scanning calorimetry (DSC; see Supplementary Figs 1 and 2). Subsequently, its relaxation behaviours were characterized using the TA Q800 dynamical mechanical analyzer (DMA) across a wide range of temperatures and frequencies. Figure 1 presents the isochronal DMA results of the alloy, including the loss modulus E″ and the storage modulus E′, as obtained from the temperature T=173–540 K at the single testing frequency f=1 Hz. Note that, as compared with the conventional DMA tests, the testing temperature range in our experiments was significantly extended with the starting point lowered down to 173 K rather than the ambient temperature. As seen in Fig. 1, it is striking that the E″ curve shows more than two distinct peaks in the given testing temperature range: besides a pronounced β- (or secondary) relaxation peak at 399 K and a α- (or main) relaxation peak at 504 K, there is another relaxation spectrum peaked at a lower temperature of 226 K, which spans a wide temperature range from below 173 to above 300 K, indicative of a broad distribution of relaxation times similar to the β relaxation. However, the amplitude or strength of the newly found peak is rather low, only about 1/100 of the α relaxation, contrasting the well-known strength of a typical β relaxation process, which is usually lower than that of α relaxation by about 1/10 (refs 27, 28). Moreover, it is worthy to mention that the storage modulus E′ shows a relatively small but noticeable drop at the temperature corresponding to the low-T relaxation peak (the encircled areas in Fig. 1), which is similar to the α and β relaxation processes and further confirms the existence of the newly found relaxation peak. For the sake of discussion, this low-T relaxation process is herein termed as the fast β′ relaxation as opposed to the conventional slow β relaxation.


Unusual fast secondary relaxation in metallic glass.

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

The emergence of two secondary relaxations in the La-based metallic glass on the isochronal dynamical mechanical spectrum.The temperature dependence of loss modulus, E″ and storage modulus, E′, was obtained at the testing frequency of 1 Hz and heating rate of 3 K min−1. The red and green regions represent the Cole–Cole (C–C) fitting of the fast β′ and slow β relaxation, respectively, while the yellow region represents the H–N fitting of the α-relaxation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: The emergence of two secondary relaxations in the La-based metallic glass on the isochronal dynamical mechanical spectrum.The temperature dependence of loss modulus, E″ and storage modulus, E′, was obtained at the testing frequency of 1 Hz and heating rate of 3 K min−1. The red and green regions represent the Cole–Cole (C–C) fitting of the fast β′ and slow β relaxation, respectively, while the yellow region represents the H–N fitting of the α-relaxation.
Mentions: For this study, we chose a La-based bulk metallic glass as the model material, which has the chemical composition of La56.16Ce14.04Ni19.8Al10 (in atomic %). As seen in the later text and Supplementary Information, this La-based metallic glass has an excellent thermal stability and pronounced β relaxation. The amorphous nature of the La-based alloy is confirmed by means of X-ray diffraction as well as differential scanning calorimetry (DSC; see Supplementary Figs 1 and 2). Subsequently, its relaxation behaviours were characterized using the TA Q800 dynamical mechanical analyzer (DMA) across a wide range of temperatures and frequencies. Figure 1 presents the isochronal DMA results of the alloy, including the loss modulus E″ and the storage modulus E′, as obtained from the temperature T=173–540 K at the single testing frequency f=1 Hz. Note that, as compared with the conventional DMA tests, the testing temperature range in our experiments was significantly extended with the starting point lowered down to 173 K rather than the ambient temperature. As seen in Fig. 1, it is striking that the E″ curve shows more than two distinct peaks in the given testing temperature range: besides a pronounced β- (or secondary) relaxation peak at 399 K and a α- (or main) relaxation peak at 504 K, there is another relaxation spectrum peaked at a lower temperature of 226 K, which spans a wide temperature range from below 173 to above 300 K, indicative of a broad distribution of relaxation times similar to the β relaxation. However, the amplitude or strength of the newly found peak is rather low, only about 1/100 of the α relaxation, contrasting the well-known strength of a typical β relaxation process, which is usually lower than that of α relaxation by about 1/10 (refs 27, 28). Moreover, it is worthy to mention that the storage modulus E′ shows a relatively small but noticeable drop at the temperature corresponding to the low-T relaxation peak (the encircled areas in Fig. 1), which is similar to the α and β relaxation processes and further confirms the existence of the newly found relaxation peak. For the sake of discussion, this low-T relaxation process is herein termed as the fast β′ relaxation as opposed to the conventional slow β relaxation.

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