Low-temperature Relaxation Peak Research Articles

High damping performances over wide temperature range in the B doped Ti-Ni shape memory alloys

• The Ti-Ni alloys with B addition undergo B2 ↔ B19′ martensitic transformation. • Two high internal friction peaks are observed in the B doped Ti-Ni alloys. • One internal friction is derived from reversible martensitic transformation. • The other originates from the interactions between boron and twinning boundaries. In present work, the microstructure, martensitic transformation behavior and damping properties of the B doped Ti-Ni shape memory alloys were investigated. The B2 parent phase and B19′ martensite phase are both detected in the whole samples, irrespective of B contents. In addition, the TiB whiskers are observed in the alloy with high boron contents. The martensitic transformation temperatures increase firstly and then decreases with the increasing of the B contents. The Ti-Ni alloys with B addition exhibit two high internal friction peaks, which are derived from the B2 ↔ B19′ martensitic transformation and interactions between boron and twinning boundaries, respectively. The tanδ of low temperature relaxation peak can be up to approximately 0.074 in the alloy with 0.7 at.% B contents. The introduction of proper interstitial atoms is considered as promising method to improve the damping performances.

Dielectric Relaxation Measurements in La<sub>2</sub>Mo<sub>1.5</sub>W<sub>0.5</sub>O<sub>9 </sub>Oxide-Ion Conductor

The effects of tungsten doping in La2Mo1.5W0.5O9 sample were studied using dielectric relaxation measurements. The results indicate that W6+ can suppress the α/β phase transition in the La2Mo2O9. Additional to the low-temperature relaxation peak Pd associated with oxygen ion diffusion, a new dielectric loss peak Ph associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution was observed around 740 K.

Low-temperature internal friction and nanostructured metal stability

The effect of aging at room temperature after equal-channel angular pressing and annealing on parameters of the low-temperature relaxation peak and dynamic Young’s modulus in nanostructured copper is studied. The dislocation nature of the peak is established. It is shown that the high rate of change for all peak parameters is observed close to the copper static relaxation temperature. The data obtained are in good agreement with results of high-temperature in situ changes of elasticity modulus and microhardness.

The Oxygen-Ion Diffusion and Phase Transition in the La<sub>2</sub>Mo<sub>2-x</sub>W<sub>x</sub>O<sub>9</sub> Samples Measured by Internal Friction Method

The effects of tungsten doping on the oxygen-ion diffusion and the phase transition in La2Mo2–xWxO9 samples (x = 0.5, 0.75, 1.0, 1.2) were studied using internal friction method. The results show that two peaks were detected in the internal friction-temperature spectra in the La2Mo2-xWxO9 samples, the low-temperature relaxation peak is associated with oxygen ion diffusion, and the high-temperature peak is associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution.

Influence of Tungsten Doping in La<sub>2</sub>Mo<sub>2</sub>O<sub>9</sub> Oxide-Ion Conductors by Dielectric Relaxation Measurements

The effects of tungsten doping in La2Mo2–yWyO9 (y =0, 0.25, 0.5, 1.0, 1.4) samples were studied using dielectric relaxation measurements. The results indicate that the solubility of W6+ in La2Mo2O9 sample is about 25mol%, W6+ can suppress the α/β phase transition in the La2Mo2O9. Additional to the low-temperature relaxation peak Pd associated with oxygen ion diffusion, a new dielectric loss peak Ph associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion distribution was observed around 740 K. The conductivity of La2Mo1.9W0.1O9 sample is higher than that of the pure La2Mo2O9, and then decrease with the increasing of the tungsten doping in La2Mo2–yWyO9 (y = 0.5, 1.0) samples in the whole measurement temperature.

NMR relaxation and rattling phonons in the type-I Ba8Ga16Sn30clathrate

Atomic motion of guest atoms inside semiconducting clathrate cages is considered as an important source for the glasslike thermal behavior.69Ga and 71Ga Nuclear Magnetic Resonance (NMR) studies on type-I Ba8Ga16Sn30 show a clear low temperature relaxation peak attributed to the influence of Ba rattling dynamics on the framework-atom resonance, with a quadrupolar relaxation mechanism as the leading contribution. The data are analyzed using a two-phonon Raman process, according to a recent theory involving localized anharmonic oscillators. Excellent agreement is obtained using this model, with the parameters corresponding to a uniform array of localized oscillators with very large anharmonicity.

Phase transition associated with the variation of oxygen vacancy/ion distribution in the oxide‐ion conductor La2Mo2–xWxO9

AbstractThe effects of tungsten doping in La2Mo2–x Wx O9 samples (x = 0, 0.1, 0.25, 0.5, 0.75, 1.0, 1.2, 1.4) were studied using dielectric relaxation measurements. Additional to the low‐temperature relaxation peak Pd associated with oxygen ion diffusion, a new dielectric loss peak Ph was observed around 740 K. With increasing tungsten concentration, the activation energy of peak Pd increases and saturates at a value of about 1.45 eV, and the height of peak Ph increases at first and then decreases after passing a maximum at 25% tungsten doping. With increasing measurement frequency, the height of peak Ph decreases monotonically but its position shifts very little. Peak Ph in pure and tungsten‐doped La2Mo2O9 is suggested to be associated with a phase transition from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase transition process in oxide-ion conductor β-La2Mo2−xWxO9 assessed by internal friction method

The oxygen ion diffusion and phase transition in La2Mo2−xWxO9 (x=0, 0.25, 0.75, 1.0, and 1.4) have been investigated by the internal friction method. In addition to the low-temperature relaxation peak associated with oxygen ion diffusion, an internal friction peak of phase transition type is observed around 350°C in all tungsten substituted La2Mo2O9 compounds. Based on the behavior of this peak and the ionic conduction properties, the mechanism of this peak is suggested to be associated with a transition from static disordered state to dynamic disordered state of oxygen ion distribution in anion sublattice that most probably results in a transition of the ionic conduction from the Arrhenius type to the Vogel-Tamman-Fulcher type.

A Study on the Low Temperature Internal Friction Relaxation Peak in a Ti<SUB>49.8</SUB>Ni<SUB>50.2</SUB> Alloy

The low temperature relaxation peak appearing around 200 K in Ti49:8Ni50:2 shape memory alloy is a multiple relaxation process with activation energy Q ¼ 0:39 eV and frequency factor f0 ¼ 6:2 � 10 9 s � 1 and is associated with the interaction of dislocations with pinning vacancies. Due to the increase of dislocation density and the annihilation of quenched-in vacancies after thermal cycling, the height of relaxation peak PR decreases with increasing the number of thermal cycling. Higher amounts of dislocation-vacancy reaction cause a higher relaxation damping under the condition of higher quenching temperature. The quenched-in vacancies can have a significant effect on the transformation rate, and thus the heights of transformation peaks PH1 and PC1 decrease with increasing quenching temperature. Dislocations introduced by both thermal cycling and quenching from high temperature will depress the martensitic transformation, and hence decrease the peak temperatures of PH1 and PC1.

Thermal Properties of Aromatic Polycarbonates Copolymers Based on Bisphenol A and Tetramethyl Bisphenol A

AbstractStatistical copolycarbonates containing different bisphenol A/tetramethyl bisphenol A (BPA/TMBPA) molar ratios were synthesized by polycondensation reaction between a mixture of the two bisphenols and phosgene. The reaction conditions were selected for producing polymers having comparable molecular weights (M̄n≈9000 g/mol) but different composition, and the same composition but different molecular weights.The calorimetric properties of the products were investigated by differential scanning calorimetry (DSC) and dynamical‐mechanical thermal analysis (DMTA). In particular, the effect of the copolymers molecular characteristics on the glass transition temperature (Tg) and the related relaxation processes were studied.DMTA was employed for evaluating the effect of macromolecular structure on the γ low temperature relaxation peak.

Morphology and dielectric properties of an epoxy network modified by end‐functionalized liquid polybutadiene

AbstractEpoxy resin networks modified with different functionalized liquid polybutadiene were characterized by scanning electron microscopy, atomic force microscopy (AFM), and dielectric thermal analysis techniques. Different morphologies were observed for these different systems, which were attributed to different interaction degrees between the components. Hydroxyl‐terminated polybutadiene (HTPB) and carboxyl‐ terminated polybutadiene (CTPB) resulted in epoxy networks with two‐phase morphology that differed in rubber particle size. The use of isocyanate‐terminated polybutadiene (NCOTPB) resulted in transparent thermoset material, whose rubber domains were in the nanoscale dimension, only detected by the AFM technique. The different morphological aspects in these epoxy systems also affected the dielectric properties. The epoxy–HTPB network exhibited two low temperature relaxation peaks corresponding to two different phases present in the system, whereas the epoxy–CTPB or epoxy–NCOTPB systems, whose rubber particles are well adhered to the epoxy matrix by chemical bonds, displayed only one single low temperature relaxation peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4053–4062, 2004

Molecular Motions of Non-Crystalline BEK

Relaxation behaviors of BEK, a new engineering plastic with high heat resistance (T g: 181° C, T m: 364° C), were investigated. Dielectric relaxation peaks were observed at -83° C and 51° C in 9.8 Hz, and their activation energies were 7 kcal/mol and 19 kcal/mol, respectively. The relaxation peaks were also observed in mechanical measurements. The `chemical structure-relaxation behavior' relationship in BEK and its related polymers suggests that the origins of the high temperature relaxation peak of BEK are crankshaft type chain motions while those of the low-temperature relaxation peak are wigglings of benzonitrile or phenyl groups.

Structural relaxation of aluminum-lanthanide metal-transition metal amorphous alloys upon low temperature annealing

Structural relaxation of Al 90− x Ln x Ni 10 (Ln = Y, La or Ce) and Al 74Ce 6Ni 10M 10 (M = Fe, Co, Ni or Hf) amorphous alloys was examined by differential scanning calorimetry. Changes in the maximum differential specific heat, δC p, max, and reversible enthalpy relaxation, δH endo, with annealing temperature, T a, show at two-stage relaxation in Al 90− x Ln x Ni 10 alloys exhibiting a glass transition, T g. Twe two stages include a low-temperature stage that peaks at a T g of about 150 K and a high-temperature stage at a temperature just below T g. By comparing the compositional dependence of ΔC p, max ( T a) and ΔH endo ( T a) as well as the activation energies, Q m, for the low- and high-temperature relaxations with the melting temperatures of Al 11Ln 3 and Al 3Ln compounds, the low-temperature relaxation is attributed to a local range atomic rearrangement of the AlNi pair with weak bonding and the high-temperature relaxation to the medium-range cooperative atomic regrouping of AlLn and NiLn pair with strong bonding. The high-temperature relaxation is not present in the Al 74Ce 6Ni 10M 10 alloys that crystallize before T g. The low-temperature relaxation peak of the Al 74Ce 6Ni 10M 10 alloys shifts to a higher temperatures in the order of Hf < Ni < Co < Fe and this compositional dependence is interpreted by taking the bonding nature of Ce and M atoms into consideration.

The orientation dependence of the low temperature relaxation peak in Nb+O+H

The orientation dependence of the low temperature relaxation peak in Nb+O+H

Study of mechanical relaxation processes in ladder organosilicon polymers

Dynamic viscoelastic properties of ladder polyorganosiloxanes have been studied by the method of induced resonance oscillations in the temperature range from −150 to 300°C and in the frequency range from 8 to 300 Hz. Two broad maxima of mechanical losses were observed for all the polymers studied independently of their chemical structure, a low-temperature maximum in the −150 to 0°C region and a high-temperature maximum in the 0 to 250°C region. It was found that the introduction of alkyl groups into polyphenylsilsesquioxanes does not noticeably affect the position and nature of the low-temperature relaxation peaks but in certain cases leads to an increase in the dynamic modulus in polyphenylalkylsilsesquioxanes, compared with the modulus of polyphenylsilsesquioxane in the same temperature region. In the high-temperature region, a distinct dependence is observed of the relaxation peak on the length and the content of alkyl groups in the polymer. It has been found that increase in the length and the content of alkyl groups is accompanied by a shift in the peak in the direction of low temperatures and a decrease in the value of the modulus. Hypotheses have been suggested on the nature of the shifts which lead to the relaxation peaks observed in the ladder polyorganosiloxanes.

Relation of the köster effect to low-temperature internal friction peaks in deformed copper

A study is made to determine the relationship between the Köster effect, i.e. the modulus defect due to dislocations which is present in a freshly deformed sample and which subsequently anneals out, and the various low temperature relaxation peaks which have been observed. It is shown that the Köster modulus defect at room temperature is made up of several parts. The largest fraction corresponds to dislocation motion which contributes to the high-temperature side of the Bordoni peak and also to the subsidiary Niblett—Wilks peak. About 40% of the Köster modulus defect is still present at 5°K. The significance of the present results to the interpretation of the Bordoni relaxation is discussed. In particular, it is shown that these results are consistent with a mechanism for which the relaxation time depends on a power of the dislocation loop length.

Review of low temperature relaxation peaks

A brief survey is given of the Bordoni-type relaxation peaks that are observed in plastically deformed materials at low temperatures. The differences in the behavior of these peaks in materials of different space lattices are emphasized.