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The stress-induced reorientation of the low-symmetry defects due to substitution atom pairs can give rise to an internal friction peak (Zener relaxation) and the first-nearest-neighbor substitutional atom pairs are plainly considered as the dominant contribution. Here, the Zener relaxation in the body-centered cubic (BCC) FeGa single crystals with different orientations was investigated, which against intuition originates primarily from the stress-induced reorientation of the second-nearest-neighbor Ga-Ga atom pairs. This Ga-Ga atom pair configuration is prevalent at high temperatures as directly observed by high-temperature in situ electron microscopy experiments. This phenomenon establishes non-ambiguously a direct correlation between Zener relaxation strengths and magnetostrictive properties. In addition, it was found that the diffusion activation energy of Ga atoms in FeGa single crystals is significantly lower than that in other iron-based alloys, suggesting that this value is closer to the actual diffusion activation energy of Ga atoms in FeGa alloys. These findings offer valuable insights into the study of short-range ordering in BCC alloys and the exploration of their functional properties. [Display omitted] [ABSTRACT FROM AUTHOR]

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.

Zener type relaxation in Fe-Ga based alloys with Ga content from ∼8 to ∼28 at.% were identified and studied using the Dynamical Mechanical Analyser (DMA) and a Forced Torsion Pendulum (FTP). The Zener relaxation caused by reorientation of pairs of Ga atoms in Fe was used to evaluate the activation parameters of Ga atom jumps in Fe. An increase in the relaxation strength occurred with an increase in the Ga content up to 19 at.% according to an increase in the number of Ga-Ga atom pairs (Δ∼C Ga 2 (1-C Ga ) 2 ), whereas a decrease in the relaxation strength from 19 to 28 at.% Ga was assigned to D0 3 and L1 2 ordering of Ga atoms in Fe-Ga alloys. Ordering and phase transitions in these alloys affected the Zener relaxation parameters and led to the appearance of transient anelastic effects. A study of several ternary Fe-Ga-Al alloys using both temperature dependent and isothermal mechanical spectroscopy (frequency variations from 10 −4 –10 2 Hz) was conducted to avoid transient effects which take place at heating or cooling, and to measure anelasticity of alloys in the equilibrium state for the chosen temperatures. The Arrhenius treatment of relaxation effects in single- and poly-crystals allows identifying the Zener effects in ternary alloys and to analyse them with respect to alloy structures. [ABSTRACT FROM AUTHOR]

Abstract: An advanced intermetallic γ-TiAl-based alloy containing Nb and Mo has been studied to understand the microscopic mechanisms taking place during thermal treatments carried out to adjust a fine, nearly lamellar microstructure. The evolution of the microstructure has been characterized by high-energy X-ray diffraction and electron microscopy, while the atomistic mechanisms of defect mobility have been studied through internal friction and dynamic modulus measurements. An internal friction relaxation peak has been observed at about 1050K (for 1Hz) in the initial oversaturated α2-Ti3Al phase, whose intensity strongly decreases after precipitation of the γ-TiAl laths. The activation parameters of this relaxation have been measured, Hact =3.1±0.05eV, τ 0 =8.3×10−17 s and β =1.3, and the relaxation is attributed to a point defect mechanism taking place inside the supersaturated α2-Ti3Al phase. A new Zener-like atomistic model based on stress-induced reorientation of Al–VTi–Al dipoles has been developed to explain the observed relaxation, resolving the controversy concerning the relaxation peak at 1050K present in many γ-TiAl-based alloys. Precipitation of the γ-lamellae has also been considered as being responsible for the dynamic modulus hardening and, additionally, for another contribution to the internal friction at higher temperature than the described relaxation. Finally, the theoretical Debye equations as a function of temperature, for both internal friction and dynamic modulus, have been applied, using the measured activation parameters, to perform a deconvolution of the relaxation and precipitation contributions. The obtained results agree well with the experimental ones at different frequencies, allowing a global interpretation of the involved atomic processes. [Copyright &y& Elsevier]

Abstract: A new sub-resonant inverted torsion pendulum has been used to measure the internal friction and dynamic modulus of an Fe–38at.% Al alloy as a function of temperature from 600 to 1350K and constant oscillating frequency ranging from 0.01 to 3Hz. Two internal friction peaks and a background increasing exponentially with temperature were observed. Both peaks overlap and have different shifts to lower temperatures with decreasing frequency indicating different involved relaxation mechanisms. We measured the activation parameters of the main peak. Finally we applied a recently proposed model to remove the high-temperature internal friction background and perform a spectra de-convolution to find the parameters characterizing both relaxations. The mechanisms responsible for both relaxations are discussed. [Copyright &y& Elsevier]

Abstract: In Fe–Si–Al–C alloys, point-defect relaxation includes both the interstitial carbon Snoek-type relaxation, split into a “pure iron” (Fe–C–Fe) Snoek peak and an “interstitial–substitutional” (Fe–C–Me; Me=Al, Si) peak, and the substitutional Zener relaxation. The influence of Al and Si, with varying Al/Si ratio, on these effects is used to study the qualitative characteristics of substitutional–interstitial (Si–C, Al–C) and substitutional–substitutional (Al–Al, Si–Si, Al–Si) interactions in these alloys. Concerning the latter, there is a mutual compensation of the elastic distortion fields, produced in the Fe matrix by the relatively bigger Al and smaller Si atoms, respectively, which largely suppresses the Zener relaxation in the ternary Fe–Si–Al alloys, probably without affecting the elastic dipole strength of interstitial carbon. From the kinetic behavior of the two components of the Snoek-type relaxation, it is concluded that the substitutional–interstitial interaction is generally attractive and sufficient for modifying the distribution of the C atoms, but not for trapping to become dominant. [Copyright &y& Elsevier]

Abstract: Atomic ordering and stress-induced ordering (Zener relaxation) were studied in a series of 18-carat (75wt%) yellow gold alloys (Au–Cu–Ag) by means of isothermal mechanical spectroscopy with a forced torsion pendulum at low frequencies. In the high-temperature solid solution, the Zener peak increases critically according to a Curie–Weiss type law when approaching the transition temperature to the ordered phase from above, then breaks down and disappears as the alloy orders. The two critical temperatures as well as the activation energy for the Zener relaxation are reported for each alloy of the series. The composition dependence of the two ordering phenomena is discussed, including the aspect of phase separation into a copper-rich and silver-rich phase as predicted by the ternary phase diagram. [Copyright &y& Elsevier]

• The internal friction (IF) phenomena were systematically studied in long-term annealed Fe-(0−30) at% Ga alloys. • The rapid decay temperature of the high damping plateau decreases with increasing Ga content in Fe-Ga alloys. • A new IF peak associated with Zener relaxation in the FCC structured L1 2 phase of Fe-Ga alloys was observed. • The phase transition peak observed in Fe-30at%Ga is attributed to L1 2 →A2/B2. The internal friction (IF) phenomena were systematically studied in a temperature range from room temperature (RT) to 800 °C for Fe-(0−30) at% Ga alloys annealed at 480 °C for 14 days, which include the magnetic-related high damping plateau (HDP) and the point of ferro-paramagnetic transition (T c), grain boundary relaxations, Zener relaxations, and the IF peaks associated with phase transitions. It was found that the rapid decay temperature of the HDP decreases with increasing Ga content, which is consistent with the variation of the Curie point (T c), and the HDP disappears when the Ga content is greater than 18 at%. In the long-term annealed Fe-30at%Ga alloy, a frequency-independent phase transition IF peak was observed and its mechanism was suggested as the phase transition of L1 2 →A2/B2. The phase transitions in Fe-(0–30 at%)Ga alloys evaluated by the IF technique are in good agreement with the equilibrium phase diagram. In addition, a new relaxation peak was observed before the displacive phase transitions of L1 2 →D0 19 and L1 2 →A2/B2, and its mechanism could be related to Zener relaxation in the FCC structured L1 2 phase. [ABSTRACT FROM AUTHOR]

Abstract: We have measured the internal friction and the dynamic modulus of an Fe–38at.% Al alloy using a forced torsion pendulum working between 10−3 and 10Hz. The measurements have been carried out as a function of temperature (from room temperature to 1200K) and as a function of frequency. Two peaks have been observed in the internal friction spectra, at about 780 and 1100K, which are largely superposed in the intermediate temperature range. Both peaks and the corresponding modulus defect shift in temperature with the oscillation frequency, and can be attributed to relaxation mechanisms. Previous results in the literature seem to indicate that the low temperature peak is the Zener relaxation of Al atoms. The activation energy of the high-temperature peak, referred to as P1 peak because it has not been studied previously, has been determined to be H act =2.87eV, from the results of measurements at different temperatures and frequencies. We discuss the possible mechanisms, which could be responsible of this P1 peak, and suggest that it could be attributed to the intrinsic movements of 〈100〉 perfect dislocations over the Peierls barrier by kink pair formation in the B2 ordered FeAl. [Copyright &y& Elsevier]

Abstract: The Zener relaxation in three Fe–Al alloys with 22, 26 and 28at.% Al has been studied by isothermal measurements of elastic-energy-dissipation as a function of vibrating frequency in the range from 10−4 to 102 Hz. The activation energy of the Zener relaxation has been determined as follows (in kJ/mol): 238 in Fe–22Al of the disordered bcc (A2) structure, 270 in Fe–22Al of the D03 +A2, two phase structure, 235 in Fe–26Al of the B2 ordered structure, 286 in Fe–26Al of the D03 ordered structure, and 276 in Fe–28Al–3Cr at temperature close to the D03 ↔B2 transition. [Copyright &y& Elsevier]

By means of the vibrating-reed technique the temperature and magnetic field dependencies of internal friction and elastic modulus have been measured for ferromagnetic single and polycrystals of D03 ordered Fe3Al. Specimens with different content of carbon showed the expected variation of the Snoek peak (at around 500 K) which changed its height drastically from the heating to the cooling run, and could be reproduced in its original height by a quenching treatment. This indicates some immobilization and remobilization of carbon probably in carbide precipitates. Quenching and subsequent annealing also causes a slight shift of the position of the Snoek peak while the Zener peak (at about 900 K) remains unchanged. The elastic modulus shows a pronounced ΔE-effect changing with thermal treatments. [Copyright &y& Elsevier]

Abstract: The mechanical loss and dynamic modulus temperature spectra of two 18-carat white gold alloys, Au58%Cu24%Pd18% without (grade A) and with alloying additions (grade B), were measured in the 400–1000K temperature range. A peak interpreted as a Zener relaxation peak is found at about 630K in both alloys. In the as-quenched state the peak shifts to lower temperatures due to excess vacancies, creating a transient peak at 520K visible only upon the first heating. In grade A, a relaxation peak is observed at 750K and is attributed to grain boundary relaxation, since it is absent in monocrystalline sample. In the same temperature region, the grade B features a peak with a large hysteresis between heating and cooling. A sharp peak observed in heating at 830K is accompanied by a strong modulus decrease. In cooling, we observe a peak at 750K, below which the mechanical loss abruptly decreases, accompanied by a modulus recovery. The peak hysteresis is interpreted as being due to dissolution or precipitation, respectively. The internal friction spectrum is correlated with the alloy''s mechanical properties, namely the hardening of the grade B upon tempering at a temperature below the dissolution peak. [Copyright &y& Elsevier]

Abstract: We conducted internal friction (IF) and elastic modulus measurements on several manganites in the temperature range 100–500K. The La1− x Ca x MnO3 series, with x=0, 0.1, 0.2, 0.33 and 1, was studied showing the magnetic phase transitions and two additional IF peaks around 320 and 400K, respectively. Both, peaks associated to relaxations, present activation enthalpies of 2–3 and 3–6eV, whose intensity depends on x. In this work we associate the 400K IF peak to a Zener relaxation of the cations that occupied the same crystallographic site. We believe that the 320K IF peak is due to different crystalline states of the samples. [Copyright &y& Elsevier]

Abstract: We have studied the temperature spectra of internal friction and relative dynamic modulus of a Cu–11.9Al–2.5Mn (wt.%) alloy. It is found that a peak appears at around 350 °C during the first heating process of the quenched specimen. The peak occurs not only during heating but also during cooling. Its activation energy has been calculated to be 1.85±0.17 eV in terms of the Arrhenius relation. In addition, the peak disappears in specimens during the second or more heating process, because an overlap occurs between the peak and the reverse martensitic phase transition peak. During cooling, however, the peak can be seen all the time. It is suggested that the peak originates from Zener relaxation. [Copyright &y& Elsevier]

The microstructure, internal friction (IF) behavior spectra, heat flow curves, and mechanical strength of Fe-18Ga- x La (x = 0.05, 0.1, 0.2, 0.5, and 1.0 at.%) alloys were systematically analyzed in this investigation. In the IF spectra, a relaxation IF peak (Labeled as P 1) and a peak related to order-disorder phase transition (Labeled as P tr) are observed in the temperature range of 400 °C–690 °C. It is found trace La doping has a significant effect on the P tr peak. With the increase of the La-doped content, the peak of P tr gradually shifts to a lower temperature and the net peak height decreases. Combining with phase diagram, DSC, Grazing Incidence X-ray diffraction (GI-XRD) spectra and SEM, the mechanisms of the reduction of both the critical temperature and the strength of P tr peak for the Fe-18Ga- x La alloy are ascribed to the precipitation of LaGa 2 phase, which reduces the Ga content gradually in the matrix. Further, the mechanism is verified in Fe-18.1Ga alloy and Fe-19.3Ga alloy. In addition, the trace La doping can significantly improve the mechanical strength of the Fe − 18Ga alloy. • A series of IF peaks were observed in Fe-18Ga- x La alloy. • Trace La doping has a significant effect on the P tr peak. • The mechanism of the reduction of the peak position is ascribed to the precipitation of LaGa 2 phase. • Trace La doping can significantly improve the mechanical strength. [ABSTRACT FROM AUTHOR]