Boundary Relaxation Peak Research Articles

Effect of Os doping on electrical properties of YMnO3 multiferroic perovskite-oxide compounds

In this study, YMnO3 (YMO) and osmium (Os) doped YMO (YMn1-xOsxO3) (x = 0.01, 0.05, 0.10) compounds were synthesized via conventional solid-state reaction and their frequency and temperature depended electrical properties were investigated by wide range dielectric/impedance spectrometer. Structural and chemical analysis of YMO and Os doped YMO powders were carried out using via scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS). Impedance measurement results revealed that only grain boundary relaxation peak observed for YMO and 1 mol% Os doped YMO whereas both grain boundary and grain relaxation peaks observed for 5 mol% and 10 mol% Os doped samples. It has been seen that resistivity of the YMO can be decreased via Os doping and we observed that 10 mol% Os doped sample has the lowest resistivity among the other samples. The activation energies of YMO and Os doped YMO compounds were calculated. The results showed that the activation energy values of studied compounds gradually decreased via increasing Os doping ratio. Moreover, it has been demonstrated that the grain boundaries have higher energies that the grains.

Internal Friction Peaks in Mg-0.6% Zr and Mg-Ni High Damping Magnesium Alloys

Abstract A broad relaxation peak, which contributes to the high damping capacity around room temperature, has been obtained in all high damping magnesium alloys. This peak is a dislocation-related relaxation peak, which is probably caused by the interaction between dislocation and point defects (vacancy and solid atoms) during the dislocation movement on the basal plane activated by heat. The grain boundary relaxation peak also has been observed in both Mg-Ni and Mg-0.6%Zr high damping alloys. However, it is necessary to point out that microstructure can affect the gain boundary relaxation. With Ni content increasing, the grain is refined and the grain boundary internal friction peak shifts to lower temperature. Compared with Mg-0.6%Zr alloy, the grain boundary internal friction peak shifts to higher temperature after adding a little yttrium (Y).

Microstructure evolution, damping capacities and mechanical properties of novel Mg-xAl-0.5Ce (wt%) damping alloys

The effect of Al content on the microstructure, damping behavior and mechanical properties of Mg-xAl-0.5Ce (wt%) damping alloys was systematically studied. Al content had a great effect on the morphology features of Al4Ce phases. The quasi-rectangular network structure was observed in as-cast Mg-1Al-0.5Ce alloy. The Al addition promoted the dynamic recrystallization during extrusion process and led to the texture weakening, but the basal texture was sharpened with further Al addition due to the consumption of the Ce solute. The as-extruded Mg-1Al-0.5Ce alloy showed the best damping capacity among as-extruded Mg-xAl-0.5Ce alloys, which was mainly ascribed to the texture weakening. The ductility was improved with increasing Al content, while the strength was reduced. This behavior was related with the texture weakening and increasing grain sizes. The as-extruded Mg-1Al-0.5Ce alloy exhibited the excellent comprehensive performance. The peak P2 of as-extruded alloys in the first heating run was a superimposed peak, consisting of a grain boundary relaxation peak and a recrystallization peak. The grain boundary peaks P2 in the second heating run shifted to lower temperatures and their activation energies decreased with increasing Al content. The reasons for the variation of the grain boundary peak P2 were discussed.

Grain Boundary Relaxation in a Fe-Cr-Al Alloy

The features of grain boundary relaxation of a (wt.%)Fe-25Cr-5Al alloy have been investigated using a multifunction internal friction apparatus. The grain boundary relaxation peak appears at about 630oC on the internal friction-temperature curves for the alloy. The peak temperature shifts toward high temperature with increasing frequency. In terms of Arrihenius relation, the activation energy is calculated to be 4.07(±0.15)eV and the pre-exponential factor is 6.2×10-24±1s. Grain boundary relaxation strength remarkably decreases with increasing grain size. When grain size reaches 520μm, the grain boundary relaxation peak almost disappears.

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

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.

The influence of thermomechanical treatment on the complex modulus of Mg alloy AZ31

Dynamic modulus analyses were performed on Mg alloy AZ31 following thermomechanical treatments to enable investigation of the influence of microstructural features created by plastic deformation on the elastic and the anelastic behavior of this alloy as quantified by variations in the complex elastic modulus (E* = E′ + iE″) with temperature. The real component or storage modulus (E′) determined for this alloy was 42.0 ± 2.5 GPa at 25 °C and it was independent of rolling direction and cold work up to 20 pct reduction in thickness. A broad peak was observed in the imaginary component or loss modulus (E″) around 175 °C (for a 1.0 Hz loading frequency), and it was determined that this peak is a superposition of at least four different relaxation mechanisms: a thermally activated mechanism related to precipitate phases near 153 °C and three peaks related to mechanical deformation at 165 °C, 188 °C, and 235 °C. The latter three peaks were also thermally activated with the activation energy determined to be 1.68 ± 0.04 eV. These mechanical relaxation peaks are attributed to microstructural features produced by cold work, and it is demonstrated that the stresses generated by cooling from heat-treatment temperatures influences these peaks. It is concluded that the grain boundary relaxation peak is above 350 °C.

Analysis of damping in particle-reinforced superplastic zinc composites

The damping behavior of superplastic zinc (SPZ) particulate composites with up to 42.5 vol pct spherical TiC particles (3 Μm in diameter) was studied in the 25 ‡C to 330 ‡C temperature range using a low frequency torsion pendulum. The observed damping at room temperature was modeled as a combination of a diffusion-controlled dislocation relaxation and a grain boundary relaxation. Addition of TiC produced a lower dislocation damping contribution at room temperature, but this loss was offset by an increased contribution from the grain boundary relaxation. An increase in the elastic modulus was also observed for the composite. The validity of a theoretical model for predicting changes in the grain boundary relaxation peak temperature resulting from the introduction of large nondeforming particles was tested. This study demonstrates that grain sliding in SPZ alloys occurs by cooperative sliding of grain clusters containing three to five grains. The activation energy for this process was found to be 111 kJ/mole (1.15 eV), which is in agreement with previously published values for grain sliding in SPZ. A second internal friction peak at a temperature just below the eutectoid transformation temperature was also observed and this peak was associated with recrystallization.

Chemical, microstructural, and internal friction characterization of Al/Cu thin-film reactions

Cu/Al bilayer reactions have been studied by Rutherford backscattering, Auger depth profiling, transmission electron microscopy (TEM), and internal friction. In the later stage of the solid-state reaction Al2Cu Θ phase growth occurs in a planar manner at the top of the Al film and additionally along the grain boundaries of the columnar Al grains. For the early stage of the reaction where only small amounts of Cu have diffused into the Al, internal friction proved to be the only experimental technique sensitive to Cu concentrations below 500 ppm. It was found that 300 ppm of Cu are already sufficient to shift the grain boundary relaxation peak observed by internal friction to higher temperatures compared to pure Al. This behavior reflects a rise in activation energy for grain boundary diffusion from 0.55 eV for Al to about 1 eV for the AlCu system. At higher Cu concentrations the grain boundary relaxation peak remains unaffected up to a Cu concentration of 5%, decreases for higher concentrations and is completely suppressed at 19%. This behavior is closely related to microstructural changes at the grain boundaries as observed by TEM.

Characterization of Thin Films by Internal Friction Measurements

ABSTRACT: Internal friction has been employed to characterize various properties of thin Al and Al-alloy films. The grain boundary relaxation peak was useda) to determine the activation energies for grain boundary diffusion in the alloy films,b) to investigate the influence of impurities on the grain boundary diffusion in Al at concentration levels as low as 300 ppm, andc) to get information about the adhesion strength between the film and the substrate.

Internal friction of iron-chromium alloys in the temperature range between 20 and 800 °c

Internal friction of a number of iron-based alloys is measured between room temperature and 800 °C. The exponentially rising damping observed above 500 °C corresponds to an activation energy which is close to the energy for self-diffusion in iron. The grain boundary relaxation peak is observed around 620 °C, in iron-chromium alloys, around 500 °C in iron with oxide additions. For chromium-free specimens, the activation energy is found to be 2.5 eV. In iron-chromium alloys, large recovery effects which are observed between 500° and 800 °C seem to be caused by processes governed by a wide spectrum of activation energies.

Grain Boundary Damping II: Iron Interstitial Alloys

Internal friction measurements of the grain boundary relaxation peak have been carried out on alloys of high purity iron containing carbon or nitrogen. The influence of these impurities on peak height, peak temperature and on the activation energy for the mechanism giving rise to the damping has been determined. The results differ from those reported on the influence of substitutional impurities. The explanation of these effects is discussed qualitatively in terms of the boundary sliding and boundary migration mechanisms.