Amplitude-independent Internal Friction Research Articles

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.

Nonlocality of Dynamic Characteristics for Edge Dislocation Segment, Elastic Interaction of Dislocation with Pinning Points, and their Effect on Dislocation AIIF

In the present work, we studied dislocation amplitude-independent internal friction (AIIF) for segment of edge dislocation. Results obtained were compared with results of the Koehler-Granato-Lücke string model. Expression for dislocation effective rigidity and effective mass, obtained earlier by applying generalized susceptibility of dislocation, is used. Dependences of dislocation effective rigidity on dislocation segment length, dislocation effective mass on frequency and segment length, internal friction on for various values of frequency and segment length are plotted. Case of elastic interaction of the dislocation segment with pinning points is also investigated. It was found that main effect of elastic interaction the dislocation with the pinning points is reduces to influence in the effective rigidity. Plots of internal friction dependence on frequency for various values of distance between the dislocation and the pinning points are constructed.

Температурные зависимости упругих модулей Юнга и внутреннего трения 12 %-х хромистых ферритно-мартенситных сталей ЭК-181 и ЭП-823 с разными режимами термообработки

The elastic (Young’s moduli) and relaxation (amplitude-independent internal friction) properties of ferritic-martensitic 12 % chromium steels EK-181 (low-activated) and EP-823, depending on their heat treatment modes (THT — traditional, CHT — combined) were investigated by the method of dynamic mechanical spectroscopy in the low-frequency range (0.5 – 30.0 Hz) and the temperature range 25 – 400 °С. Temperature, frequency and amplitude dependences of Young’s moduli and internal friction have been determined. Frequency and amplitude independence of elastic moduli is observed. The values of Young’s moduli depend on their modes of heat treatment of steels (THT, CHT) and for EK-181 steel is always higher than for EP-823 steel. The temperature dependences (spectra) of internal friction in steels for different modes of their heat treatment and at different frequencies almost monotonically increase with increasing temperature. Relaxation peaks are practically absent (within the measurement accuracy), which determines the practical absence of solid interstitial solutions (C, O, N) in the studied steels.

APPLICATION OF ACOUSTIC PULSE ECHO-METHOD FOR THE INVESTIGATION OF DYNAMIC AND STRUCTURAL DYSLOCATION CHARACTERISTICS OF CRYSTALS

The multifunctional pulse equipment allowіng to use the method of amplitude-independent internal friction in the frequency range 7.5 to 232.5 MHz is described. Equipment gjves the possibility to investigate the peculiarities of the process of phonon-dislocation interaction in crystals, to carry out thermoactivation analysis of the process of dislocation of the dislocations about the stoppers under the action of temperature and elastic loading, to study processes of dislocation and mechanical relaxation in loaded samples in the quasi-elastic and plastic strain range.

Концентрационные и диффузионные характеристики атомов внедрения (C, O, N) и модули упругости в ванадии и сплавах V – 4 Cr – 4 Ti, V – W – Cr, V – Ta – Cr – Zr

The elastic (Young’s) modulus and relaxation properties (amplitude-independent internal friction) of bcc metals and alloys (vanadium, V–4Cr–4Ti, V–W–Cr, and V–Ta–Cr—Zr alloys) have been studied in the temperature range of 25–400°С by means of dynamic mechanical spectroscopy within a low-frequency range (0.5–30.0 Hz). No carbon in vanadium and V–W–Cr alloy in solid-solution state is revealed. In the case of vanadium and V–W–Cr alloy, the solid-solution concentrations of oxygen and nitrogen and the diffusion characteristics thereof (diffusion activation energy, characteristic relaxation time, and the preexponential factor in the diffusion equation) have been determined. In the case of V–4Cr–4Ti alloy, carbon, oxygen, and nitrogen solid solutions have not been observed. In V–Ta–Cr–Zr alloy, the solid-solution concentrations of interstitial atoms (C, O, N) are substantially lower than those in vanadium and V–W–Cr alloy. The values of elastic modulus in vanadium alloys can be either higher or lower than the elastic modulus inherent in vanadium depending on type of alloy (alloying) and on temperature. The V–4Ti–4Cr alloy exhibits the smallest value of the elastic modulus among all the materials under study. The temperature curves of the elastic (Young’s) modulus for the studied materials exhibit no features, except for a slight local relaxation of the Young’s modulus in the case of vanadium and V–W–Cr alloy in the temperature range of the relaxation peaks.

THE MAIN RESULTS' OVERVIEW OBTAINED BY THE METHOD OF AMPLITUDE-INDEPENDENT INTERNAL FRICTION ON METALS AND IONIC CRYSTALS

There was made the analysis of the main findings obtained in the field of the dislocations' dynamics research using the method of amplitude-independent internal friction on different objects of study – metals and alkali-halide crys-tals. The results of Granato-Lücke string dislocation theory verification, as well as of Alshits-Indenbom quantum-mechanical theory of dynamic dislocations' damping for above-mentioned materials were considered in the paper. An analytical review of works aimed at the study of relaxation and thermally activated processes in crystals was performed here. Some promising directions for the further experimental work on this problematics there were re-vealed as a result of the study.

Аналіз результатів, одержаних на лужногалоїдних кристалах методом амплітуднонезалежного внутрішнього тертя

Аналіз результатів, одержаних на лужногалоїдних кристалах методом амплітуднонезалежного внутрішнього тертя

Investigation of recrystallization in an Al-0.3 Mg alloy by the method of internal friction

The Al-0.3 at % Mg alloy subjected to deformation by rolling (ɛ = 90%) at room temperature has been investigated by the method of internal friction. The influence of deformation and subsequent recrystallization on the temperature dependence of the amplitude-dependent and amplitude-independent internal friction has been determined. Effects of anelasticity due to recrystallization and grain-boundary relaxation have been revealed and investigated; parameters of corresponding peaks of internal friction have been determined and discussed. When studying the kinetics of recrystallization, the high sensitivity and selectivity of the procedure used have been shown.

Two descriptions of magnetoelastic energy dissipation in uniaxial trigonal antiferromagnetic materials, associated with rotations of spontaneous magnetization of their sublattices

For trigonal siderite-type antiferromagnetic materials with allowance for the crystal symmetry considered in the thermodynamic potential, it is demonstrated that an amplitude dependence of the internal friction is observed in the absence of accompanying magnetic field along the [001] easy axis, whereas in the presence of the field, the amplitude-independent internal friction component is observed. In this case, it is expedient to use the ratio of energy dissipated for the period to oscillation energy as a measure of the internal friction for frequencies ω < τ−1 (τ is the relaxation time), whereas for frequencies comparable with the Larmor frequency, the magnetic resonance phenomenon must be taken into account.

Low-temperature relaxation in faulted Cu-based martensites

An extensive investigation of elastic and anelastic properties, at an ultrasonic frequency of around 100 kHz, of a variety of binary and ternary Cu-based alloys forming faulted martensites evidences the existence of a strong anelastic relaxation over a wide temperature range propagating down to lowest temperatures achieved in experiments of around 10 K. The anelastic phenomenon observed is the most pronounced for low oscillatory strain amplitudes (approximately from 10 −7 to 10 −6) and results in a rapid decrease of Young's modulus (measured at low strain amplitudes) with increasing temperatures from the lowest values of around 10 K. The relaxation of Young's modulus is accompanied by a linear increase of the low-amplitude internal friction with increasing temperature. The low-temperature relaxational behaviour is strongly dependent on concentration of quenched-in vacancies: the relaxation is enhanced by β-phase ageing and is strongly suppressed by direct quenching of ternary Cu–Al–Ni, Cu–Zn–Al and Cu–Al–Be alloys. The anelastic effect observed exhibits an unusual property: the amplitude-independent internal friction background emerging as a result of this relaxation is non-additive with the amplitude-dependent internal friction. We suggest that this low-temperature relaxation is associated with a reversible transition from a cooperative to an individual mode of motion of the system of partial dislocations.

Internal friction and Young’s modulus of Si3N4/BN fibrous monoliths at various vibrational strain amplitudes

The effect of temperature and vibrational strain amplitude on Young’s modulus and an ultrasound damping (internal friction) of ceramic boron nitride samples and silicon nitride/boron nitride fibrous monoliths was studied. It was shown that the elastic moduli and the elastic vibration decrement of the low-modulus BN ceramic and of the high-modulus Si3N4/BN monoliths measured at small strain amplitudes (in the region of amplitude-independent internal friction) exhibit a noticeable temperature hysteresis. Temperature exerts the smallest effect on the amplitude-independent decrement and on the amplitude-dependent damping and Young’s modulus defect of a monolith whose filaments are arranged both along and perpendicular to the axis of a rodshaped sample. These parameters behave in the most complicated way in a sample with all its filaments aligned with the rod axis. The observed relations can be assigned to structural features of the monoliths and the considerable influence of transverse strain on the evolution of defect structure in the materials studied.

Shear stress at the interface of coaxial composites determined by the resonance of low-amplitude vibrations

The aim of this work is to determine the viscoelastic behaviour of the interface in a coaxial composite material made of a tough shield and a ductile core. The elastic modulus and the amplitude-independent internal friction are measured using a longitudinal oscillating resonant system at 50 kHz. The contribution of the interface is modelled as a shear stress that modifies the elastic behaviour of the constituents. The value of this shear stress is determined for different interfaces (epoxy resin-brass, epoxy resin-Pyrex and paraffin-Pyrex). The model is autovalidated by the excellent agreement between the calculated and experimental values of the internal friction (damping) of the composites.

Shock Loading Effect on the MHz-Range Amplitude-Independent Internal Friction and Elastic Properties of the ??1 Martensite Phase in Cu-Al-Ni Alloys

The internal friction spectrum at 5 MHz in the martensite β' 1 -phase of CuAlNi alloys shows two prominent internal friction peaks at 270 and 170 K. Corresponding anomalies in the sound wave velocity-temperature dependence have been observed. Detailed analysis of the behaviour of the peaks in dependence on different levels of impact loading and γ-irradiation points to dislocation-point defect interaction. It is assumed that grain boundary dislocations are responsible for the 270 K peak while lattice dislocation, existing within the martensite variants are responsible for the 170 K peak.

Structural Internal Friction in CuAlNi Crystals

Amplitude-dependent and amplitude-independent internal friction has been studied in martensite and during temperature induced martensitic transformation in CuAlNi single crystals after different heat treatments. The measurements of intrinsic damping were performed in ultrasonic and infrasonic frequency ranges. Low frequency measurements were combined with the direct observations of the stress-anelastic strain hysteretic loops. Observed regularities do not correspond to the breakaway model of amplitude-dependent internal friction both for quenched and aged samples. The conclusion is drawn, that during ageing in β-phase the behaviour of the pinning obstacles changes from highly mobile at room temperature and forming atmospheres around the mobile defects, presumably dislocations, to rather immobile and homogeneously distributed in the bulk of the crystal. Amplitude dependent and amplitude independent internal friction components, measured at ultrasonic frequencies, exhibit different temperature dependences during direct martensitic transformation. A maximum of the non-linear anelasticity was observed near the M s temperature, implying a significant contribution of the premartensitic phenomena to the amplitude-dependent internal friction due to phase transition.

Internal friction of dislocations in a magnetic field.

A theory is proposed for the influence of a magnetic field on the amplitude-independent internal friction of dislocations in metals. The theory combines the electron viscous-drag model with the possibility of the dislocation depinning from the paramagnetic centers. The theory is compared with the experimental data obtained in undeformed and deformed copper. Excellent agreement is achieved in deformed metals. For undeformed metals the agreement is good for low magnetic fields. A modulation technique is proposed that will improve greatly the precision of the measurement of the dislocation parameters.

A New Low-Temperature Dislocation-Relaxation Peak in Aluminum

Amplitude-independent internal friction measurement is made on a zone-refined aluminum single crystal between 2–240 K by a composite oscillator method. In the lightly deformed state \(({\lesssim}10^{-4})\), a new relaxation peak is clearly found at 11 K. The activation energy of this peak is derived to be about 0.01 eV by assuming the attack frequency f 0 =10 10 s -1 , and if the peak is due to the kink pair formation of the dislocation on the Peierls potential valley, the Peierls stress is estimated to be about 10 -5 µ (µ: shear modulus), which does not conflict with the yield stress of low-temperature plastic deformation measurements.

Internal Friction of Cast Graphite-Magnesium Composites

AbstractInternal friction behavior in cast 8-ply [0°1 P55Gr/Mg-0.6%Zr alloy and P55Gr/Mg-1%Mn composites as a function of vibratory strain amplitude was measured at 80 kHz using a Marxtype piezoelectric composite oscillator. Both the matrix and composite exhibited strain amplitude independent internal friction below ε ≈ 10−6, while significant strain amplitude dependence was noted at higher strain levels. A maxima in damping was observed for most of the specimens tested. Heat treatment to enlarge grain size was found to increase both the strain amplitude independent and dependent internal friction of the composite. Strain amplitude dependence of the internal friction, including the existence of the maxima, was explained by the Granato-Lucke (G-L) dislocation internal friction model. Dislocation densities obtained from various TEM images from the fiber-matrix interface were compared to values predicted by G-L theory.

Internal friction in nickel near the Curie temperature

The PUCOT has been used at 40 kHz to measure the internal friction in polycrystalline Ni over the temperature range 600–670 K for several values of applied magnetic field. The curves of the amplitude independent internal friction as a function of temperature showed maximum-minimum combinations near T c in agreement with related results of other authors. These anomalies near T c were analyzed as peaks or dips in damping. Above a field of 50 mT there was saturation of the peak height and depth of minimum. Both the peaks and dips showed thermal hysteresis suggesting that a nucleation and growth mechanism occurs near T c. It is possible that the peak or dip is associated with diffusion involving matrix atoms and clusters of atoms of the major impurities (C, O or Si). The position of the minima led to an acceptable estimate for T c of 631 K. From amplitude dependence studies the estimates for the minor loop length of the ultrasonically vibrating dislocation line (55–230 nm) were found to be less than the magnetic domain sizes (∼ 10 −5 m) in Ni confirming that the pinning of dislocations takes place on a much finer scale than the domain size. Some of the internal friction data agreed well with the predictions from the G-L theory (17) and support the damping mechanism due to pinned dislocations. Other results did not agree with the G-L model making further studies with high-purity nickel single crystals a worthwhile follow-up to this study.

Effect of hydrogen on shear modulus of polycrystalline α iron

A sensitive inverted torsion pendulum method was used to study within the temperature range from 90 to 300 K the effect of hydrogen on amplitude-independent internal friction and free oscillation frequency of high-purity iron. Gaseous hydrogen excited by electrical discharge was applied for charging a wire specimen inside the pendulum chamber. A significant reduction of pendulum frequency (and thus of shear modulus) was observed for hydrogen-containing iron at temperatures below 200 K. Desorption led to restoration of the initial frequency. At 100 K the mean relative decrease in shear modulus for hydrogen-charged iron was G = 0.16± 0.04%.

Internal-friction anisotropy in a real crystal and construction of characteristic internal-friction surfaces

General trends are examined for the anisotropy in the background amplitude-independent internal friction in a real crystal with space and time dispersion. A variational criterion is formulated to define the limits of application of the theory, and a method is proposed for constructing the characteristic internal-friction surfaces.