Temperature Dependence Of Internal Friction Research Articles

Inelastic relaxation in tin oxide thin films with an amorphous structure

Inelastic relaxation in amorphous tin oxide thin films obtained by ion-beam sputtering in an argon atmosphere were studied. The films retain an amorphous structure after annealing at temperatures below 623 K for 30 min and crystallization begins after annealing at 673 K with the formation of two phases, where the SnO2 phase predominates over the SnO phase. Annealing at 723 K for 30 min leads to a partial transition of the SnO crystalline phase to the SnO2 phase.The temperature dependence of internal friction revealed maxima at 585 K and 603 K, identified as β - relaxation maxima, as well as at 690 K, identified as α - relaxation maximum. It is assumed that the β - relaxation maxima at 585 K and 603 K are associated with local hopps of oxygen atoms within the defect structure of SnO2 and with local hopps of tin atoms within the defect structure of SnO, respectively. The exponential increase in internal friction up to a temperature of 690 K in the α - relaxation region is associated with the diffusion of nonequilibrium vacancy-like defects of the amorphous structure below the glass transition temperature and equilibrium ones above the glass transition temperature. Estimates of the migration energy and formation energy of vacancy-like defects in amorphous tin oxide were made.

Ultrabroad distribution of multiple anelasticities in O-doped refractory multiprincipal element alloys

The Snoek anelastic internal friction (IF) peak due to stress-induced dipole ordering associated with interstitial atoms was well observed in IF curves of single-principal element alloys (SPEAs) as early as in the 1950s, however, its behavior remains elusive in multi-principal element alloys (MPEAs) to date. Here the temperature-dependent IF spectra of NbTiV0.5Zr refractory MPEAs with varying O contents were presented, and the analysis of these data indicates that for O-doped NbTiV0.5Zr MPEAs, the O addition triggers two anelastic IF peaks (the PO1 and PO2), corresponding to the O-Snoek-type relaxation in random solid solution (RSS) and local chemical ordering (LCO) structures, respectively. The half-peak width of the PO1 is 2–3 times broader than that for SPEAs, associated with the wide O migration energy barrier distribution in MPEAs. These phenomena show a striking contrast to the single and narrow Snoek-type peak observed for SPEAs. Our analysis further reveals an approximate linear correlation between the half-peak width of the Snoek-type peak and the mixing entropy. The introduction of O also shifts grain boundary relaxation peaks (PG) towards higher temperatures. Interestingly, high-temperature anomalous modulus changes were observed for the first time in TiV-based lightweight refractory MPEAs, which is suggested to be originated from the order reduction of the body-centered cubic (bcc) structure at elevated temperatures. Moreover, the 1 at.%O doped NbTiV0.5Zr MPEA with a favorable balance between the peak heights of the PO2 and PG, exhibits outstanding specific yield stress (SYS) among refractory MPEAs while maintaining an elongation as high as 20 %. This work provides not only a bridge between the anelastic behavior of SPEAs and MPEAs for upcoming studies and theories concerning bcc MPEAs with interstitial atoms, but contributes to the holistic design of bcc MPEAs with high strength and excellent ductility.

Re-dissolution of precipitates in reactor pressure vessel steels evaluated by internal friction technique

The re-dissolution process of Mn-Si-rich precipitates in Fe-1.0 %Mn-0.4 %Ni-0.2 %Si (wt.%) reactor pressure vessel (RPV) model steel was assessed using the internal friction (IF) technique. A relaxation IF peak (P1), corresponding to grain boundary relaxation, was observed near 600 °C in the temperature-dependent IF curve of the as-received sample. After long-term aging at 600 °C, a significant suppression of the P1 was observed due to the extensive precipitation of Mn-Si-rich precipitates. Upon further annealing at 700–800 °C, the P1 gradually recovered with increasing annealing temperature, indicating the gradual dissolution of Mn-Si-rich precipitates along the grain boundaries. This phenomenon was consistent with transmission electron microscopy experimental results.

The Cold-Brittleness Regularities of Low-Activation Ferritic-Martensitic Steel EK-181

The behavior of the EK-181 low-activation ferritic-martensitic reactor steel (Fe–12Cr–2W–V–Ta–B) in the states with different levels of strength and plastic properties after traditional heat treatment (THT) and after high-temperature thermomechanical treatment (HTMT) in the temperature range from −196 to 25 °C, including the range of its cold brittleness (ductile–brittle transition temperature, DBTT) is studied. The investigations are carried out using non-destructive acoustic methods (internal friction, elasticity) and transmission and scanning electron microscopy methods. It is found that the curves of temperature dependence of internal friction (the vibration decrement) of EK-181 steel after THT and HTMT are similar to those of its impact strength. Below the ductile–brittle transition temperature, it is characterized by a low level of dislocation internal friction. The temperature dependence curves of the steel elastic modulus increase monotonically with the decreasing temperature. In this case, the value of Young’s modulus is structure-sensitive. A modification of the microstructure of EK-181 steel as a result of HTMT causes its elastic modulus to increase, compared to that after THT, over the entire temperature range under study. The electron microscopic studies of the steel microstructure evolution near the fracture surface of the impact samples (in the region of dynamic crack propagation) in the temperature range from −196 to 100 °C reveal the traces of plastic deformation (increased dislocation density, fragmentation of the martensitic structure) at all of the temperatures under study, including those below the cold brittleness threshold of EK-181 steel.

A study of gallium oxide by using the piezoelectric composite oscillator technique at a frequency of 100 kHz

The article presents the results of the study of the mechanical properties and defect structure of gallium oxide (Ga2O3) by using the piezoelectric composite oscillator technique. Bulk samples of the Ga2O3 beta phase in the form of single crystals and their intergrowths were obtained by growth from a melt with a shaper (Stepanov technique). The research involved studying the dependences of the longitudinal elastic modulus and the damping of elastic vibrations at a frequency of 100 kHz on the strain amplitude. Changes in the elastic and microplastic properties of the samples at different temperatures were attributed to possible relaxation phenomena in the structure of the material. Studying the defect structure in samples of pure and doped Ga2O3 is necessary to improve the technology for the production of large single crystals. The fundamental questions in this area are the influence of defects on the anisotropy of electrical conductivity, band structure, and other functional properties of the resulting semiconductor material. The purpose of this article is to establish the features of sample preparation, research, and interpretation of the results obtained by the piezoelectric composite oscillator technique for gallium oxide samples. In the studied samples, the first longitudinal vibration mode was excited, which corresponded to a length of about 27 mm and a small cross-section of the sample. The temperature dependences in the region of low and high strain amplitudes were determined separately. The crystalline quality of the prepared samples was assessed by X-ray diffraction with the analysis of the rocking curve. The value of Young’s modulus obtained along the growth axis (crystalline orientation <010>) in Ga2O3 crystals E≈260 GPa is in line with the results of previous studies. Relaxation peaks corresponding to various dislocation interactions were found on the temperature dependences of internal friction at a temperature of 280 K

(Digital Presentation) Internal Friction, Mechanical Spectroscopy in SiO2/Si Wafers

Introduction The electrophysical properties of semiconductor devices significantly depend on the perfection of their structure. It is necessary to control the structure of semiconductor wafer-plates disks in the manufacture of large integrated circuits (LIC). Technique was developed and device was made that allows to obtain the information about structural defects in such disks by attenuating elastic oscillations Q-1 to study the defects density nd and the depth hd of their propagation. Defect annealing leads to change in the shape of internal friction (IF) temperature spectrum Q-1(T) [1]. IF method allows to set the spectrum of structural defects on the analysis of positions of maximums IF, on duration of relaxation time τ and on their deposit in attenuation of elastic vibrations [2]. A non-destructive method for the technological control of the structure defects by measuring internal friction (IF) and elastic modulus E after laser radiation was developed. Experimental procedure Ultrasonic (US) pulse-phase method using USMV-LETI, modernized USMV-KNU and computerized “KERN-4” with frequencies f║ ≈ 1 MHz and f┴ ≈ 0,7 MHz, US invariant-polarization method for determining the effective acoustic μil and elastic constants Cijkl were used [3,4,5]. The measured velocity error was equal to ΔV/V = 0.5÷1,5%. The study of influence of structure defects on damping of vibrations in Si/SiO2 wafer-plates by the diameter of D = 100÷60 mm and by the thickness of hSiO2 ≈ 600 nm, hSi ≈ 470 000 nm, allows to estimate the degree of perfection of crystalline structure. Metallography optical supervision of microstructure by means of the microscope ”LOMO MVT”, atomic-force microscopy (AFM) were used. Results and discussion The quasi-longitudinal US velocity V║[001] = 5870 m/s, elastic modulus E001 = ρV║[001] 2 = 80,28 GPa for SiO2/Si from the oscillogram were determined. Temperature dependence of internal friction Q-1(T) in SiO2/Si wafer-plate p-type, doped with B, KDB-7.5(100) diameter D ≈ 76∙10-3 m, thickness hSi ≈ 460∙103 nm with SiO2 layer thickness hSiO2 ≈ 100 nm after X-ray irradiation with dose Dγ ≈ 102 Gy is showed. Conclusions It was found that as the result of the structural defect annealing IF background Q0 -1 significantly decreases during measuring of IF temperature dependence Q-1(T), which indicates the improvement of SiO2/Si crystal structure.The elastic modulus Е, the shear modulus G, Poisson coefficient μ, IF Q-1 are dependent from SiO2/Si wafer-plate anisotropy.The value of IF background Q-1 0 after temperature T, mechanical treatments describes the changes of the elastic stress σi fields in SiO2/Si wafer-plate.The study of vibrations of disk wafer-plate Si/SiO2 at different harmonic frequencies f0, f2 made it possible to develop the technique for determining the structural defects density nD for semiconductor wafers-substrates.The relationship between IF Q-1 value, the logarithmic decrement of ultrasound damping δ and the dislocations density nD was established for disk-shaped semiconductor wafers-substrates. Acknowledgements This work has been supported by Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv.

Regularities of Changes in the Physico-Mechanical and Corrosion Properties of Reinforcement Steel Grade 23Kh2G2T

The purpose of the work was to study of the regularities of changes in the physico-mechanical and corrosion properties of reinforcing steel 23Kh2G2T in hot-rolled and heat-treated (furnace tempering) states.Methods. The study of the physical and mechanical properties and resistance (long-term corrosion resistance) of bar reinforcement to stress corrosion cracking (SCC) was carried out on experimental melts of steel grade 23Kh2G2T. The choice of melts was made in such a way that their chemical composition corresponded, if possible, to the upper, middle and lower levels of the grade composition.To create experimental conditions as close as possible to operational ones, the tests were carried out in a boiling solution of nitrates (60% Ca(NO3)2 + 5% NH4NO3 + 35% H2O) at a temperature of 110°С and operating voltages σe = (0,1–0,8 )σВ. To elucidate the features of transformations occurring in steel during tempering, the temperature dependences of internal friction were taken from samples tempered at different temperatures.Processing of the results of the time dependence of the amplitude-independent internal friction was carried out according to the theory of Granato, Hikata, Lucke, which describes the kinetics of the return of internal friction due to the migration of point defects to dislocations.Results. It has been established that by controlling the chemical composition and technological regimes for the production of steel 23Kh2G2T, it is possible not only to sharply increase its resistance to cracking, but also to obtain a guaranteed complex of mechanical and corrosion properties. It was revealed that reinforcement made of 23Kh2G2T steel should be produced with mandatory tempering. The greatest resistance to stress corrosion cracking with practically unchanged strength for reinforcement made of steel 23Kh2G2T is provided by 2-hour tempering in the temperature range of 350…400°С.Conclusion. The results obtained can be used to establish patterns of behavior of various types of ingot, powder and composite materials with high dispersion in phase and structural components in various conditions and states.

Internal Friction and Mechanical Spectroscopy of SiO2/Si, Nanocomposites of Multiwalled Carbon Nanotubes and Polyamide, Polyethylene, Polyvinyl Chloride, Expanded Polystyrene

: In this work after X-ray irradiation outcomes of the evaluation of dynamic characteristics interstitial atoms Sij, vacancy V and O-complexes was applied for account of a condition of an annealing with the purpose of deriving specific structural defects in SiO2/Si wafer-plate. The nondestructive method, which is allow to determine from internal friction difference ΔQ-1/Q-1 0 of elastic vibrations structure defects density Nd and the depth of broken layer hb, is offered for SiO2/Si wafer-plates. 1. Introduction Defect annealing leads to a change in the shape of the internal friction (IF) temperature spectrum Q-1(T) [1]. IF method allows to set the spectrum of structural defects on the analysis of positions of maximums IF, on duration of relaxation time τ and on their deposit in attenuation of elastic vibrations [2]. A non-destructive method for the technological control of the structure defects by measuring internal friction (IF) and elastic modulus E after laser radiation was developed. 2. Experimental procedure Ultrasonic (US) pulse-phase method using USMV-LETI, modernized USMV-KNU and computerized “KERN-4” with frequencies f║ ≈ 1 MHz and f┴ ≈ 0,7 MHz, US invariant-polarization method for determining the effective acoustic μil and elastic constants Cijkl were used [3,4]. The measured velocity error was equal to ΔV/V = 0,5÷1,5%.The study of influence of structure defects on damping of vibrations in Si/SiO2 wafer-plates by the diameter of D = 100÷60 mm and by the thickness of hSiO2 ≈ 600 nm, hSi ≈ 470 000 nm, allows to estimate the degree of perfection of crystalline structureMetallography optical supervision of microstructure by means of the microscope ”LOMO MVT”, atomic-force microscopy (AFM) were used. 3. Results and discussion The quasi-longitudinal US velocity V║[001] = 5870 m/s, elastic modulus E001 = ρV║[001] 2 = 80,28 GPa for SiO2/Si from the oscillogram were determined. Temperature dependence of internal friction Q-1(T) in SiO2/Si wafer-plate p-type, doped with B, KDB-7.5(100) diameter D ≈ 76∙10-3 m, thickness hSi ≈ 460∙103 nm with SiO2 layer thickness hSiO2 ≈ 100 nm after X-ray irradiation with dose Dγ ≈ 102 Gy is showed. 4. Conclusions 1. The growth of internal friction maximum height QM -1 testifies the growth of the structural defects concentration n, and the broadening of internal friction maximum ΔQM -1 here represents the relaxation process of structural defects new types in SiO2/Si wafer-plate.2. It was found that as the result of the structural defect annealing IF background Q0 -1 significantly decreases during measuring of IF temperature dependence Q-1(T), which indicates the improvement of SiO2/Si crystal structure.3. The elastic modulus Е, the shear modulus G, Poisson coefficient μ, IF Q-1 are dependent from SiO2/Si wafer-plate anisotropy.4. The value of IF background Q-1 0 after temperature T, mechanical treatments describes the changes of the elastic stress σi fields in SiO2/Si wafer-plate.5. The study of vibrations of disk wafer-plate Si/SiO2 at different harmonic frequencies f0, f2 made it possible to develop the technique for determining the structural defects density nD for semiconductor wafers-substrates.6. The relationship between IF Q-1 value, the logarithmic decrement of ultrasound damping δ and the dislocations density nD was established for disk-shaped semiconductor wafers-substrates. Acknowledgements This work has been supported by Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv.

Enhancing damping capacity and mechanical properties of Al-Mg alloy by high strain rate hot rolling and subsequent cold rolling

The damping capacity of high Mg alloyed Al-Mg alloy (Al-9.2Mg-0.8Mn-0.2Zr-0.15Ti) prepared by high strain rate hot rolling (HSRR) and subsequent cold rolling (CR) are carefully studied. Both the strain amplitude dependent internal friction (ADIF) at room temperature and the temperature dependent internal friction (TDIF) at elevated temperature are detected by a dynamic mechanical analyzer (DMA). The results indicate that the subsequent cold rolling can significantly improve the damping capacity of the alloy. The as-CRed alloy exhibits higher strength and better damping capacity than the as-HSRRed alloy, with the ultimate tensile strength (UTS) of 606 ± 6 MPa, the elongation to rupture of 11.6 ± 0.6% and the Q-1 value of 0.019 at room temperature with the strain of 1 × 10-3 and the frequency of 1 Hz. The room temperature damping of the as-CRed alloy is mainly ascribed to the low stacking fault energy (SFE), the high dislocation density and the finer broken second phase particles. Moreover, the as-CRed alloy also presents excellent high temperature damping, with the maximum Q-1 value of 0.212 ± 0.003 at 361 ℃ with the frequency of 1 Hz. The relatively high damping capacity of the cold rolled sheet for a given frequency and temperature can be attributable to the special microstructure characteristics including the high dislocation density, the elongated lamellar grains with shear bands and the high fraction of LAGBs.

Phase transition and defect relaxation behavior in a medium manganese steel

Phase transition and defect relaxation behavior of a Fe-7Mn-0.1C medium manganese steel have been systematically studied mainly by using internal friction (IF) technique. From temperature-dependent IF curves in both heating and cooling processes, two relaxation IF peaks (the P1 located at ~ 200 °C on heating and the P2 at ~ 550 °C on cooling) and two phase transition IF peaks (the Ptr1 located at ~ 670 °C on heating and the Ptr2 at ~ 300 °C on cooling) were observed. The P1 peak disappears when the cementite (θ) particles and/or retained austenite (γR) exist in the microstructure, and is associated with the Snoek-Kê-Köster relaxation (SKK relaxation). The P2 peak is suggested to be originated from grain boundary relaxation in austenite (γ). The formation mechanisms of the Ptr1 and the Ptr2 come from reverse austenitic transformation (RAT) and martensitic transformation (MT), respectively. In addition, the apparent asymmetry of the Ptr1, the variation of peak height, the difference between the Ptr1 and Ptr2 peaks, and the effect of IF studies on the mechanical properties are discussed in detail in the present work. These results provide a valuable reference for the design of high-performance medium Mn steels.

Влияние дислокационных и двойниковых структур на механические характеристики сплавов Ni–Mn–Ga на ультразвуковых частотах

Magnetic shape memory alloys are a specific subtype of shape memory materials. The magnetic deformation phenomenon causes the high research interest in these alloys. Thus, in one of the most promising alloys based on Ni–Mn–Ga, using a magnetic field, it is possible to achieve changes in a single crystal size by up to 10 % due to the reorientation of the magnetic field in magnetic domains. The high magnetic deformation is directly related to the high mobility of twin boundaries separating two domains. In this work, the authors used a composite piezoelectric oscillator at a frequency of about 100 kHz to determine the influence of such defects as dislocations and twin boundaries on the mechanical characteristics of Ni49Mn30Ga21. The authors investigated the features of temperature dependences of internal friction in the samples before and after deformation and provided the amplitude dependences of these characteristics. In the studied single-crystal martensitic phase, the transition from the tetragonal phase to the orthorhombic phase was detected at 235 K. In the Ni–Mn–Ga tetragonal phase, the formation of new defects contributes to the more pronounced and early onset of amplitude-dependent internal friction. At lower loads, the successive stages occur associated with the processes of dislocations and twin boundaries movements inside the Cottrell clouds, dislocations and twin boundaries movement outside the Cottrell clouds, and supposedly, the slowdown of dislocations and twin boundaries movement due to their interaction. As well as internal friction, the authors studied the change in Young’s modulus. Its decrease at all temperatures is most pronounced in the samples with the defective structures. The study identified that in the orthorhombic phase, it is possible to observe the internal friction dependence on the deformation amplitude at a lower load due to an increase in the twin boundaries mobility with increasing temperature.

Effect of phase composition on the internal friction and magnetostriction in the L12/D03 biphase Fe-27Ga alloys

Fe-Ga alloys exhibit unique functional properties such as magnetostriction and high damping that can be adjusted by the phase transitions (D03 to L12) through a proper compositions and heat treatments. In this paper, the effect of phase composition on the internal friction (IF) and magnetostriction in Fe-27Ga alloys were systematically investigated. It was found that proportion of L12 phase in the biphase (L12/D03) Fe-27Ga alloys can be controlled by adjusting the annealing temperature and holding time. Two temperature-dependent IF peaks, i.e., a Snoek-type relaxation peak (P1) associated with the stress-induced jump of interstitial C atoms in the bcc-derived D03 phase and a Zener-type relaxation peak (P2) associated with stress-induced jump of Ga-pairs in the D03 phase were observed. The height of both peaks decreases gradually with the increasing content of L12 phase. The absolute value of magnetostriction at an applied magnetic field higher than 2000 Oe and the amplitude-dependent IF at a strain amplitude up to 10−3 decreases at first and then increases with the increasing content of L12 phase. With the increasing strain amplitude, magneto-mechanical damping of D03 phase increases at first and then decreases, while that of the L12 phase increases monotonously. This indicates that the magnetic domain walls of D03 phase can move easily under a low stress, while those of L12 phase can be driven only when the stress is high enough. Such researches could provide a design concept for high damping Fe-Ga alloys to meet the requirements in different application fields such as micro-vibration field, strong vibration field, magnetic or non-magnetic field.

Enhancement of the magneto-mechanical properties in directional solidified Fe80Al20 alloys by doping Tb

Enhancement of the magneto-mechanical properties in directional solidified Fe80Al20 alloys by doping Tb is demonstrated. The ΔE effect of 9.1%, large magnetostriction of 144 ppm, magnetostriction sensitivity of 0.28 ppm/Oe, ΔG effect of 5.4%, and magneto-mechanical coupling of 29.74% reached for Fe79.9Al20Tb0.1 alloy are beneficial for applications. The increased magnetostriction with increasing the Tb content x from 0 to 0.1 is related to the increased degree of (110) texture with Tb doping. Notably, the increased magnetostriction sensitivity, resulted from the increased magnetostriction with Tb-doping, leads to the enhancement of ΔE and ΔG effects. Nevertheless, the degraded (110) texture for higher Tb content (x = 0.15) results in the reduction of magneto-mechanical properties. Summarized with the experimental measured and theoretically estimated results, the micro eddy-current mechanism mainly governs the change of damping capacity with H for frequency of vibrations ~ 2.0 kHz resulting from the magnetic domain wall motion. Moreover, the amplitude and temperature dependences of internal friction and elastic modulus data, measured by DMA, including damping capacity and Young’s modulus, at a frequency of 0.1–30 Hz could characterize hysteretic damping and anelastic effects at heating. The result of this study suggests a cost-effective and simple method to obtain Fe80Al20 based alloy with excellent magneto-mechanical properties via proper Tb-doping.

Low-frequency internal friction in ferroelectric Ba0.8Sr0.2TiO3 and Ba0.8Sr0.2TiO3 + 0.2 mass. % La ceramics

The temperature dependences of internal friction and Young’s modulus in ferroelectric Ba0.8Sr0.2TiO3 ceramics under bending oscillations were investigated at frequencies of the several hertz. The effect of the heating rate and the frequency of oscillations on the internal friction peak height near the Curie temperature was studied. The fluctuation model of low-frequency internal friction is used to explain the obtained dependences and to estimate the nuclei volume of a new phase arising at a phase transition. After a dc electric field switched on in the ferroelectric phase, the time decrease of internal friction was observed, which had an exponential form. The addition of 0.2 mass. % La in Ba0.8Sr0.2TiO3 led both to an increase in the internal friction level in the ferroelectric phase and to a decrease in the internal friction maximum near the Curie temperature. In the first case, this was explained by a decrease in the interaction energy of charged point defects with ferroelectric domain walls, and in the second case, by the pinning of domain walls by lanthanum ions.

Thermo-kinetic modelling of the giant Snoek effect in carbon-supersaturated iron

Snoek relaxation in interstitial bcc solid solutions is the origin of the Snoek peak in frequency-dependent and temperature-dependent internal friction measurements. When applied to low-carbon steels, the internal friction profiles show a linear dependence of the peak height with carbon content. However, recent Monte Carlo simulations of frequency-dependent internal friction exhibited a non-linear giant peak height at high carbon contents. To investigate this effect in temperature-dependent internal friction, we developed a thermo-kinetic mean-field theory of the Snoek relaxation phenomenon. By taking into account the collective behaviour of the interstitial atoms, our theory predicts (i) a non-linear dependence of the peak height with composition when approaching the order–disorder transition of the alloy; (ii) a shift in the temperature of the peak; (iii) a composition-dependent activation enthalpy of the relaxation time. The theory is exemplified by the case of carbon-supersaturated iron.

Mechanical spectroscopy of phase transitions in Fe–(23–38)Ga-RE alloys

Anelastic effects in Fe-(23–38)Ga binary and ternary alloys doped with rare-earth (RE) elements, RE = Pr, Sm, Tb, Er, and Yb, are studied in a sub-resonance frequency through heating and cooling in the range from 0 to 600 °C. In situ neutron diffraction, vibrating sample magnetometry (VSM), and differential scanning calorimetry (DSC) are used to trace phase transitions during heating and cooling and to interpret anelastic effects due to phase transitions. Besides the thermally activated effects, two transient effects due to the first-order transitions D03 → L12 and B2/D03 → Fe13Ga9 (later in alloys with Ga content>29 at%) are studied. In most cases, the RE elements decrease the rate of phase transitions. The obtained results demonstrate an excellent correlation between temperature-dependent internal friction, in situ neutron diffraction, and vibrating sample magnetometry tests.

Temperature Dependence of Internal Friction of Peptides.

Internal friction is a valuable concept to describe the kinetics of proteins. As is well known, internal friction can be modulated by solvent features (such as viscosity). How can internal friction be affected by environmental temperature? The answer to this question is not evident. In the present work, we approach this problem with simulations on two model peptides. The thermodynamics and relaxation kinetics are characterized through long molecular dynamics simulations, with the viscosity modulated by varying the mass of solvent molecules. Based on the extrapolation to zero viscosity together with scaling of the relaxation time scales, we discover that internal friction is almost invariant at various temperatures. Controlled simulations further support the idea that internal friction is independent of environmental temperature. Comparisons between the two model peptides help us to understand the diverse phenomena in experiments.

On the intrinsic dissipation and fracture fatigue entropy of metals

Determination of the fracture fatigue entropy (FFE) in materials requires a proper assessment of the intrinsic dissipation terms in the entropy production equation. In this paper, physical terms that contribute to internal friction and their implications on measuring FFE in metals are discussed. We show that internal friction is one of the terms in the intrinsic dissipation equation that cannot be neglected even for low-cycle fatigue tests (LCF). Relevant to measuring internal friction, we also introduce a technique to identify the fatigue limit of metals by measuring their damping value at different stress levels. Fatigue tests are performed to examine the validity of the proposed technique for two types of steels (SS 304 and SS 1018). By comparing our results with the available data in the literature, we find that the discrepancy is less than 10%. The temperature dependence of internal friction for SS304 specimens is also investigated. The result demonstrates a linear relationship and the existence of a peak.

Идентификация релаксационных максимумов внутреннего трения в сплаве Zr – Nb после азотирования, окисления на воздухе и науглероживания in situ

The internal friction method was used to study the behavior of the Zr – 1 wt. % Nb alloy after oxidation in air, nitriding in an atmosphere of technical nitrogen, and in situ carburization during measurements. In this case, carbon was deposited on the samples during measurements due to thermal decomposition of vapors of diffusion oil. The pressure in the system was about 10–2 Pa. The temperature dependence of the logarithmic decrement of damped bending vibrations with a frequency of 2.2 – 2.4 Hz was measured on specimens in the form of a rectangular plate 22 × 8 × 0.3 mm in size. The measurements were carried out at a constant heating rate of about 4 K/min from room temperature to 700 – 750 °C. The obtained temperature dependences of internal friction were divided into partial maxima using a special program. The program determines the temperatures of the relaxation maxima and calculates the effective activation energy using the Werth — Marx formula. The internal friction spectra in successive measurements on one sample changed due to the diffusion redistribution of the alloy components. The parameters of the relaxation maxima for carbon (153 – 159 kJ/mol), oxygen (203 – 207 kJ/mol) and nitrogen (235 – 238 kJ/mol) in the alloy under study, depending on the experimental conditions, have been established. Grain-boundary (Gb) impurity maxima due to these impurities were also found. The following activation energies were obtained: 173 – 179 kJ/mol for C-Gb, 216 – 219 kJ/mol for O-Gb and 222 – 229 kJ/mol for N-Gb. Impurity grain-boundary maxima associated with carbon, oxygen, and nitrogen were observed in each series of measurements. The activation energy of the grain-boundary maxima proper decreases monotonically from 202.4 to 194.5 kJ/mol in a series with oxidation in air (experiments 711 – 715), and remains about 200 kJ/mol in nitrided samples.

Behavior and mechanism of internal friction peak in quenched Fe-18 at.% Ga alloy

Quenched Fe-18 at.% Ga with high magnetostrictive properties has a peak (Pwq) in temperature-dependent internal friction (IF) spectrum near 320 °C, which disappears for both as-cast and furnace-cooled alloys. However, the mechanism of this peak is not well understood. In this investigation, the behavior and mechanism of this peak were systematically studied. It is found that the Pwq appears when the sample is quenched from a temperature higher than the critical temperature of the order-disorder phase transition and disappears when annealed at 300 °C for 1 h. The Pwq becomes gradually more apparent as the Ga content increases from below ~18 at.%, and the Pwq almost disappears when the Ga content equals 23 at%. Combined with deformation and XRD studies, the Pwq does not originate from the vacancies and dislocations produced by the high-temperature quenching process or a phase transition from D03 to L12, and potential formation mechanisms for the Pwq may originate from the transition of Ga-rich Guinier-Preston (GP) zones to D03 structures or lattice relaxation related to Ga-rich GP zones.