Low Frequency Relaxation Effect Observed in Al-Mg Alloy

2012 ◽  
Vol 184 ◽  
pp. 149-154 ◽  
Author(s):  
N. Benyahia ◽  
Michel Gerland ◽  
C. Belamri ◽  
Andre Rivière
Keyword(s):  
Low Frequency ◽  
Relaxation Effect ◽  
Solution Temperature ◽  
Transient Effects ◽  
Mechanical Spectroscopy ◽  
Slow Cooling ◽  
Thermally Activated ◽  
Measurement Experiment ◽  
Frequency Relaxation ◽  
Large Frequency

Al-12 wt% Mg alloys have been studied by isothermal mechanical spectroscopy. The samples were quenched then annealed at various temperatures. Experiments were performed in a very large frequency range (10-4Hz – 50 Hz) between room and solidus temperatures. For each temperature of measurement, experiment started after complete microstructure stabilization of the sample and therefore the transient effects due for instance to β (( and β′ precipitation were not observed. Nevertheless, a new relaxation effect was obtained in the reversion temperature range. This effect is not thermally activated. It is maximal at about 0.1 Hz and increases with the temperature of measurement. It completely disappears after annealing at solid solution temperature and successive slow cooling and therefore is linked to the β precipitates. This effect is interpreted as a phase transformation at the precipitate surface induced by the applied stress.

Eutectoid Al-51at%Zn Alloy Studied by Isothermal Mechanical Spectroscopy

2012 ◽  
Vol 184 ◽  
pp. 167-172 ◽  
Author(s):  
Andre Rivière ◽  
Veronique Pelosin ◽  
Michel Gerland
Keyword(s):  
Transition Temperature ◽  
Low Frequency ◽  
Mechanical Spectroscopy ◽  
Thermally Induced ◽  
Atom Diffusion ◽  
Thermally Activated ◽  
Relaxation Parameters ◽  
Zn Alloy ◽  
Large Frequency ◽  
Internal Friction Spectra

sothermal mechanical spectroscopy measurements were performed in an Al-51 at % Zn alloy at various temperatures below and above the eutectoid transition temperature: during a heating the α-β eutectoid mixture changes into α solid solution at 550 K. Damping experiments were performed in a very large frequency range (10-5– 50 Hz) between room temperature and 673 K. Internal friction spectra performed between 200 K and 540 K, exhibit two thermally activated relaxation peaks (P1 and P2). P1 decreases and disappears with the increase of measurement temperature while P2 appears and increases. P2 totally disappears above the eutectoid transition temperature. Above 550 K, a new peak (P3) is evidenced at very low frequency. The relaxation parameters of P3 (limit relaxation time τ0= 9×10-7and activation energy H = 105 kJ/mole (1.1 eV)) allow to associate this peak with the motion of sub grain boundaries. P1 and P2 (τ0≈ 10-7and H ≈ 70 kJ/mole (0.75 eV) for both peaks) are associated with a thermally induced atom diffusion across the α-β interface.

scholarly journals Mechanical Spectroscopy Of Ordered Binary Au-Cu

2015 ◽  
Vol 60 (3) ◽  
pp. 2093-2096 ◽  
Author(s):  
I. Tkalcec ◽  
D. Mari ◽  
R. Schaller
Keyword(s):  
Single Crystal ◽  
High Temperatures ◽  
Low Frequency ◽  
Ordered Structure ◽  
Mechanical Spectroscopy ◽  
Antiphase Boundaries ◽  
Slow Cooling ◽  
Ordered Structures ◽  
Frequency Peak ◽  
Lower Background

Abstract We have studied a binary Au-Cu single crystal by mechanical spectroscopy. Upon very slow cooling from high temperatures, additional relaxation peaks arise at lower frequencies in isothermal spectra after the disappearing of the Zener peak below 665 K due to ordering. A high transient peak is visible at 660 K and it progressively disappears on cooling until 625 K. Another high peak is clearly visible upon following heating until 660 K. Above that temperature it decreases in parallel with the increase of the Zener peak. If the ordered structure is obtained by slowly heating the sample that has been quenched from the disordered state, no low-frequency peak is visible in the isothermal spectra, only a much lower background, which further decreases in parallel with the reappearance of the Zener peak. The low frequency relaxations are possibly due to the movement of antiphase boundaries and twin interfaces in the ordered structures.

Low Frequency Dielectric Relaxation and Charge Transport in Bi12TiO20 Photorefractive Sillenite Crystals

2017 ◽  
Vol 753 ◽  
pp. 163-167
Author(s):  
Rene Alejandro Castro ◽  
Nadezhda Ivanovna Anisimova ◽  
Liliya Ansafovna Nabiullina ◽  
Evgeny Borisovich Shadrin
Keyword(s):  
Charge Transport ◽  
Dielectric Relaxation ◽  
Transport Mechanism ◽  
Low Frequency ◽  
Frequency Range ◽  
Thermally Activated ◽  
Relaxation Polarization ◽  
Polarization Mechanism ◽  
Frequency Relaxation ◽  
Thermally Activated Process

Features of processes of a dielectric relaxation and charge transport in photorefractive sillenite crystals Bi12TiO20 at low frequency range are investigated. It was found that the dispersion of dielectric permittivity ε' in crystals Bi12TiO20 is characterized by its growth with lowering frequency and rising temperature. This behaviour may be related to existence of dipole-relaxation polarization mechanism. The frequency dependence of dielectric loss tgδ reveals the existence of low frequency relaxation peaks in the studied temperature range. From the conductivity dependence on the frequency and temperature it was found that conductivity σ increases as frequency increases in the low frequency range. The observed dependence σ(ω)≈Аωs indicates that transport mechanism is due to hopping of carriers via localized electron states. The charge transport is thermally activated process in which activation energy Ea = (0.82±0.03) eV.

Mechanical Spectroscopy of Nanocrystalline Metals

2000 ◽  
Vol 634 ◽  
Author(s):  
E. Bonetti ◽  
L. Pasquini ◽  
L. Savini
Keyword(s):  
Mechanical Behavior ◽  
Low Frequency ◽  
Creep Recovery ◽  
Mechanical Spectroscopy ◽  
Gas Condensation ◽  
Thermally Activated ◽  
Grain Sizes ◽  
Mechanical Attrition ◽  
Nanocrystalline Iron ◽  
Disorder Degree

ABSTRACTThe mechanical behavior of nanocrystalline iron and nickel prepared by mechanical attrition and inert gas condensation was investigated using mechanical spectroscopy techniques in the quasi static-and low frequency dynamic stress-strain regimes. The measures were performed on samples previously stabilized by thermal annealing at low homologous temperatures. The results of elastic energy dissipation, creep, and creep recovery measurements performed in the low strain regime (ε = 10−5−10−3) allowed to trace a phenomenological picture of the anelastic and viscoplastic behavior of nanocrystalline Ni and Fe in the 300-450 K range with different grain sizes and interfaces disorder degree. Activation energies of the thermally activated anelastic and plastic mechanisms responsible for the mechanical behavior have been evaluated.

Low Frequency Mechanical Spectroscopy of High Damping Mg-3wt.%Ni Alloy

2010 ◽  
Vol 146-147 ◽  
pp. 1761-1764
Author(s):  
Di Qing Wan ◽  
Ya Juan Liu
Keyword(s):  
Grain Boundary ◽  
Low Frequency ◽  
Mechanical Analysis ◽  
Mechanical Spectroscopy ◽  
Temperature Dependent ◽  
Thermally Activated ◽  
Ni Alloy ◽  
Dislocation Movement ◽  
Boundary Relaxation ◽  
Two Peaks

The Dynamic Mechanical Analysis (DMA) was applied to investigate the low frequency mechanical spectroscopy response of as-cast high damping Mg-3wt.%Ni hypoeutectic alloys. There are two peaks appearing on the temperature dependent damping spectrum (-100 - 420 °C). The broad peak P1 is overlapped by some small peaks due to the thermally activated dislocation movement, while the P2 peak is a solute grain boundary relaxation peak.

Investigating the dielectric properties and low-frequency relaxation process of TlGaSe2 crystals

2017 ◽  
Vol 31 (12) ◽  
pp. 1750134 ◽  
Author(s):  
Oktay Samadov ◽  
Oktay Alakbarov ◽  
Arzu Najafov ◽  
Samir Samadov ◽  
Nizami Mehdiyev ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Relaxation Time ◽  
Constant Electric Field ◽  
Low Frequency ◽  
Constant Field ◽  
Impedance Spectra ◽  
Ionic Contribution ◽  
Frequency Relaxation ◽  
Average Relaxation Time ◽  
Diagram Analysis

The dielectric and impedance spectra of TlGaSe2 crystals have been studied at temperatures in the 100–500 K range in the alternating current (AC [Formula: see text]1 V). It has been shown that the conductivity of TlGaSe2 crystals is mainly an ionic characteristic at temperatures above 400 K. The well-defined peak at the frequency dependence of the imaginary part of impedance [Formula: see text] is observed in the 215–500 K temperature range. In a constant field, there occurs a significant decrease in electrical conductivity [Formula: see text] in due course. The ionic contribution to conductivity (76% at [Formula: see text]) has been estimated from a kinetic change in electrical conductivity [Formula: see text] under the influence of a constant electric field. The diagram analysis in a complex plane [Formula: see text] has been conducted by applying the method of an equivalent circuit of the substation. It has been determined that the average relaxation time of the electric module of the sample is [Formula: see text].

High-Temperature Mechanical Relaxation due to Dislocation Motion inside Dislocation Networks

2008 ◽  
Vol 137 ◽  
pp. 21-28 ◽  
Author(s):  
Andre Rivière ◽  
Michel Gerland ◽  
Veronique Pelosin
Keyword(s):  
Internal Friction ◽  
Relaxation Effect ◽  
Dislocation Motion ◽  
Relaxation Peak ◽  
Mechanical Relaxation ◽  
In Situ Tem ◽  
Mechanical Spectroscopy ◽  
Internal Friction Peak ◽  
First Case ◽  
Dislocation Walls

Internal friction peaks observed in single or polycrystals are clearly due to a dislocation relaxation mechanism. Because a sample observed by transmission electron microscopy (TEM) often exhibits in the same time various dislocation microstructures (isolated dislocations, dislocation walls, etc.) it is very difficult to connect the observed relaxation peak with a particular dislocation microstructure. Using isothermal mechanical spectroscopy (IMS), it is easier to compare, for instance, the evolution of a relaxation peak with measurement temperature to the microstructural evolution observed by in-situ TEM at the same temperatures. IMS was used to study a relaxation peak in a 5N aluminium single crystal firstly 1% cold worked and then annealed at various temperatures. TEM experiments performed in the same material at various temperatures equal to the temperatures used for the damping experiments made possible to link this internal friction peak with a relaxation effect occurring inside dislocation walls. In two other experiments in a 4N aluminium polycrystal and in a metal matrix composite with SiC whiskers, it is shown that the observed relaxation peaks are connected to the motion of dislocations inside polygonization boundaries in the first case and in dislocation pile-ups around each whisker in the second one. Theoretical models proposed to explain such relaxation peaks due to a dislocation motion inside a dislocation wall or network are discussed.

Low-Frequency Relaxation Phenomena in α-LiIO3: The Nature and Role of Defects

2002 ◽  
Vol 168 (1) ◽  
pp. 76-84 ◽  
Author(s):  
Y. Mugnier ◽  
C. Galez ◽  
J.M. Crettez ◽  
P. Bourson ◽  
C. Opagiste ◽  
...  
Keyword(s):  
Low Frequency ◽  
Relaxation Phenomena ◽  
Frequency Relaxation

Dynamics of Ferroelectric and Nematic Liquid Crystals Confined in Porous Matrices

1994 ◽  
Vol 366 ◽  
Author(s):  
Fouad M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Heterogeneous Media ◽  
Volume Fraction ◽  
Low Frequency ◽  
Pore Wall ◽  
Polar Molecules ◽  
Average Pore ◽  
Surface Polarization ◽  
The Difference ◽  
Frequency Relaxation

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of collective modes of ferroelectric (FLC) and molecular motion of nematic (NLC) liquid crystals with polar molecules confined in silica macroporous and microporous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%) respectively. For FLC the Goldstone and the soft modes are found in macropores. The rotational viscosity associated with the soft mode is about 10 times higher in pores than in the bulk. These modes are not detected in micropores although low frequency relaxation is present. The last one probably is not connected with the nature of liquid crystal but is associated with surface polarization effects typical for two component heterogeneous media. The difference between the dynamics of orientational motion of the polar molecules of NLC in confined geometries and in the bulk is qualitatively determined by the total energy Fs of the interaction between molecules and the surface of the pore wall, which is found Fs ≈ 102erg/cm2.

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