Amplitude-dependent Internal Friction Research Articles

Contribution of phase and structural transformations to linear and nonlinear mechanisms of anelasticity in binary Al-Mg alloys

Effects of the processes of the recrystallization and precipitation of the β phase in Al-(0.3–12%)% Mg alloys on the mechanisms of grain-boundary relaxation and dislocation-induced microplasticity have been studied in some detail. The decrease in the dislocation density due to the process of recrystallization of cold-worked alloys leads to the formation of a pseudopeak in the curves of the temperature dependence of internal friction and to a decrease in the critical amplitude of deformation necessary to initiate dislocation motion in a stress field. The precipitation of the β phase in the structure suppresses the mechanism of grain-boundary relaxation; the dissolution of the β phase, which leads to the formation of impurity atmospheres, then to the passage of magnesium atoms into the solid solution, impedes dislocation motion. Depending on the total content of Mg in the alloy, the dislocation mobility upon the measurements of amplitude dependences of internal friction can be described in terms of either breakaway or friction models. The characteristics of grain-boundary relaxation and dislocation-impurity interaction and of their temperature dependences have been estimated quantitatively.

Амплитудно-зависимое внутреннее трение и генерация гармоник в средах с гистерезисной нелинейностью

Амплитудно-зависимое внутреннее трение и генерация гармоник в средах с гистерезисной нелинейностью

Internal friction in a Ni–Ti-based glassy-crystal alloy

Abstract Dynamic mechanical behavior of the Ni 40 Cu 10 Ti 33 Zr 17 alloy containing high-temperature cubic and glassy phases was studied in pseudo-elastic mode at relatively small deformations. Amplitude dependent internal friction was measured by increasing the maximal strain amplitude e 0 step by step. Two types of tests were applied: a simple test with increase in the amplitude of strain (loading) within each step of loading and a hysteresis loop measurement test. At least three hysteresis loops ‘loading–unloading’ we measured at each step, and the maximal amplitude was increased at each subsequent step. The results indicate that martensitic transformation in this composite alloy starts in a pseudo-elastic deformation mode and contributes to the internal friction observed in the studied alloy.

Role of the β-phase in grain boundary and dislocation anelasticity in binary Al–Mg alloys

Abstract Temperature- and amplitude dependent internal friction (IF) of cold-worked, annealed and quenched Al–Mg alloys with 0.3–12 wt.%Mg is studied in the range from room temperature to 600 °C. Two thermally activated relaxation peaks, named P1 and P2 in the order of increasing temperature, are recorded. The first one (P1), with activation parameters H ≈ 1.1 eV, τ 0 ≈ 10 −13 s, relaxation strength Δ ≈ 0.008, and broadening parameter β τ ≈ 2 (for 1 Hz), is recorded only in Al–Mg alloys with 8–12%Mg predominantly in the as-quenched state, and classified as a Zener relaxation mechanism. The second one (P2, above 200 °C) is found at lower Mg contents (up to 5%) mainly in single-phase states (α solution of Mg in Al), with apparent parameters H ≈ 2 eV, τ 0 from 10 −16 to 10 −21 s, Δ up to 0.3 and β τ from 3 to 6. It is partly suppressed from the low-temperature side in Al–4Mg and Al–5Mg, due to precipitation of the β (Al 3 Mg 2 ) phase at the grain boundaries, and vanishes in the two-phase states of alloys with 8–12%Mg. The relaxation mechanism of P2 is associated with grain boundary sliding. At first heating from the cold-worked state, a recrystallization ‘pseudo’ peak is dominating in all alloys, whose position and height depend on degree of deformation, heating rate, vibrating frequency and chemical composition. Amplitude dependent damping measured during recrystallization demonstrates decreases in dislocation density and in critical stress for dislocation motion. Interaction energy ‘dislocation–point defects’ in Al–Mg alloys is estimated using amplitude dependent internal friction tests at different temperatures.

Effect of Mn and Cr additions on kinetics of recrystallization and parameters of grain-boundary relaxation of Al-4.9Mg alloy

Methods of microstructural analysis, measurements of hardness, and temperature and time dependences of internal friction (TDIF and TDIF(iso), respectively) have been used to study recrystalliza� tion in coldrolled alloys and grainboundary relaxation in annealed alloys. A complex analysis of the effect of additions of transition metals (Mn, Cr) on the magnitude of the activation energy of the background of the internal friction in deformed and annealed states and on the activation parameters of grainboundary relax� ation has been performed. Methods of amplitude dependences of internal friction (ADIF) have been used to determine the critical amplitude that corresponds to the beginning of microplastic deformation in the alloys at different temperatures.

Effect of prior deformation on internal friction in a FeNi based austenitic alloy

Effect of prior deformation on strain amplitude-dependent internal friction has been studied in a FeNi based austenitic alloy subjected to solution and peak-aged treatment. The internal friction initially shows increase and then decreases with pre-strain increase in solution-treated alloy. Nevertheless, it is interesting to find that the internal friction shows continued increase with prior deformation degree in peak-aged alloy. Results could be explained using the breakaway model of dislocation in both state alloys. The discrepancy of internal friction behavior, correlated to dislocation arrangement observation, is discussed in terms of slip mode transition from wavy slip to planar slip with introduction of coherent precipitation particles.

Strain amplitude-dependent internal friction of as-cast high damping magnesium alloy during cyclic vibration

An investigation on strain amplitude-dependent internal friction (IF) of an as-cast high damping Mg-7 wt% Ni alloy was carried out. In the range of our tested strain amplitudes, whether the strain amplitude is increasing or decreasing, the strain amplitude-dependent IF curve can be divided into two stages: one is the strain amplitude weakly dependent part and the other is the strain amplitude strongly dependent part. However, after several cyclic vibrations, the IF values measured during the strain amplitude increasing are smaller than those obtained during the strain amplitude decreasing. The phenomenon is also observed at 100 °C. Partial dislocations generate a short-range slip under the cyclic stress to be responsible for it. At the first certain cycle measurement, it was also found that IF value is completely reversible; no amplitude hysteresis loop appears. During the cycle number increasing, however, it was found that the IF value tested is smaller while increasing the strain amplitude than that obtained while decreasing the strain amplitude.

A study of softening processes in heating of cold-deformed sheets of low-alloy aluminum alloys

Processes of polygonization and recrystallization in aluminum alloys with 0.3 at.% magnesium, zinc, or copper and their structure and hardness are investigated. The temperature, time, and amplitude dependences of internal friction are determined. A comparative analysis of the dislocation structure in the alloys is conducted.

Effect of microadditions of magnesium and zinc in aluminum upon heating of cold-rolled sheets

Methods of structural investigations, measurements of hardness, temperature, time, and amplitude dependences of internal friction have been used to study processes of polygonization and recrystallization in Al-0.3 at % Mg and Al-0.3 at % Zn alloys. It has been established that the magnesium atoms more efficiently pin dislocations in the aluminum-based alloys as compared to zinc atoms. Therefore, in the alloy with zinc the process of polygonization occurs more intensely and the processes of softening upon recrystallization occur more slowly than those in the alloy with magnesium.

On the damping capacity of cast irons

The treatment of experimental data on the amplitude-dependent internal friction (ADIF) in terms of various theoretical models has revealed a staged character and the main mechanisms of the processes of energy dissipation in graphite with increasing amplitude of vibrations upon cyclic loading. It is shown that the level of the damping capacity of lamellar cast iron depends on the relationship between the elastic and strength characteristics of graphite and the matrix phase. In cast irons with a rigid matrix structure (pearlite, martensite), the energy dissipation is determined by the volume fraction and morphology of the initial graphite phase. In cast irons with a softer metallic phase (ferrite), the contact interaction of graphite inclusions with the matrix and the properties of the matrix introduce additional sources of high damping.

Amplitude-dependent internal friction, hysteretic nonlinearity, and nonlinear oscillations in a magnesite resonator

The results of experimental and theoretical studies of low-frequency nonlinear acoustics phenomena (amplitude-dependent loss, resonance frequency shifts, and a generation of second and third harmonics) in a magnesite rod resonator are presented. Acceleration and velocity oscillograms of vibrations of the free boundary of the resonator caused by harmonic excitations were measured and analyzed. A theoretical description of the observed amplitude dependences was carried out within the framework of the phenomenological state equations that contain either of the two types of hysteretic nonlinearity (elastic and inelastic). The type of hysteresis and parameters of acoustic nonlinearity of magnesite were established from comparing the experimental measurements with the theoretical dependences. The values of the parameters were anomalously high even when compared to those of other strongly nonlinear polycrystalline materials such as granite, marble, limestone, sandstone, etc.

Internal friction study of the stress relaxation behavior in Cu–Ni–P alloys

The strain-amplitude dependence of internal friction in Cu–Ni–P alloys has been investigated to evaluate nondestructively the stress relaxation resistance. Annealing at 250 °C after cold rolling causes a suppression of the strain-amplitude dependence with increasing annealing time in the range between 10 and 10 4 s. It is revealed that the stress relaxation resistance linearly improves as the microplastic strain evaluated from the amplitude-dependent internal friction decreases.

Amplitude Dependent Damping of Aluminum-Matrix-Nanoparticle-Composites

Aluminum-matrix-nanoparticle-composites were produced by ball milling of micro scale aluminum powder in air atmosphere with subsequent consolidation by hot extrusion and also additional hot swaging. They were investigated in this condition after step by step isochronal annealing with successive increasing annealing temperature and quenching into water to room temperature. The material was investigated by amplitude dependent damping, hardness and density measurements, all at room temperature. For all measured amplitude dependent internal friction (ADIF) curves the damping increases with increasing strain amplitude. After some annealing treatments a knee occurs in the medium strain amplitude region of these curves. Moreover between annealing temperatures from 360°C to 480°C the strain dependent damping becomes a maximum, i.e. a peak in the ADIF curves occurs. Other ADIF curves of quenched and fatigued material show characteristic peaks that can be attributed to individual single cracks. It is shown that all these effects are due to the formation, opening and compression of cracks present in the sample or created by thermally exerted stresses.

Stress Relaxation Behavior of Cu-Ni-P Alloys Evaluated from Amplitude-Dependent Internal Friction

The strain-amplitude dependence of internal friction in Cu-0.41Ni-0.11P (mass%) alloys has been evaluated to reveal the relation between the amplitude-dependent internal friction and the stress relaxation performance. Annealing at 250°C after cold rolling causes a suppression of the strain-amplitude dependence with increasing annealing time in the range between 10 s and 104 s. Analysis of the amplitude-dependent internal friction reveals the plastic strain of the order of 10-9 as a function of effective stress on dislocation motion. It is found that the microflow stress at a constant level of plastic strain increases with increasing annealing time. This result is in line with the improvement in the stress relaxation performance but disagrees with a decrease in the tensile strength and yield stress after annealing. We believe that the increase in the microflow stress after annealing is caused by inhibition of dislocation motion due to Ni-P clusters, which were revealed by three-dimensional atom probe (3DAP) experiments.

Effects of Pinning and Atomic Ordering on Damping Properties and Martensitic Transformation of Copper-Based Shape Memory Alloys

The effects of long-range atomic order and pinning of interfaces on anelastic properties of Cu-based martensite have been distinguished by means of studying strain amplitude dependences of internal friction and Young’s modulus defect, assuming that low-and high-amplitude stages of the strain amplitude dependence correspond to the oscillations within and beyond pinning atmospheres.

Amplitude Dependent Internal Friction of Magnesium Alloy AZ31 at Room Temperature

The aim of this work is to study the Amplitude Dependent Internal Friction (ADIF) of magnesium alloy AZ31 at room temperature at the frequency 20kHz. The internal friction of AZ31 at room temperature is mostly influenced by mechanical cycling at strain amplitudes in the microplastic deformation region. An excited state of the AZ31 alloy, which can be associated with a higher internal friction and lower dynamic modulus than usual state, was found immediately after mechanical cycling. When the strain amplitude drops, the diffusion of solute atoms restores the Zener atmosphere and the internal friction relaxes exponentially with the second root of time. The measurement methodology and obtained results are presented.

Interaction Potential between a Dislocation and a Pinning Atom in FCC Metals

Amplitude dependent internal friction (ADIF) was measured on 4N and 6N Cu crystals at 4K–40 K to study the interaction between a dislocation and a pinning atom. The temperature dependence of the stress amplitude necessary to produce a constant ADIF was well explained by assuming the Cottrell type interaction potential based on linear elasticity. This is clearly different from the case of Al crystals where it was necessary to consider a modified Cottrell potential including a deviation from linear elasticity near the dislocation center.

Internal Friction Study of Vacancy Hardening in B2 Fe Al Alloys

nternal friction behaviour of B2 FeAl alloys has been examined to reveal the correlation of the microplasticity and thermal vacancies. The internal friction peak for Fe60Al40 appears at around 550 K, and the peak height increases with increasing quenching temperature. The curves of internal friction against the strain amplitude shift to larger strain amplitude as the quenching temperature increases. Analysis of the amplitude-dependent internal friction provides the plastic strain of the order of 10-9 as a function of effective stress on dislocation motion. It is found that the microflow stress at the plastic strain of 1×10-9 increases linearly with the square root of the net peak height. Remarkably, the microflow stress decreases with rising temperature but turns to increase above 500 K when measured after holding for 1 h at test temperatures. The anomalous increase in the microflow stress is caused by the creation of thermal vacancies at intermediate temperatures.

Damping behavior of Ti50.1Ni49.9 alloy in reverse martensitic transformation region

Damping behavior of Ti50.1Ni49.9 shape memory alloy during reverse martensitic transformation has been investigated by dynamic mechanical analyzer in a dual-cantilever mode. With the increase of strain amplitude, internal friction (IF) of the alloy increases in martensite and austenite states while decreases in transformation region. Based on the regularity of IF attenuation in isothermal condition, IFTr and (IFPT+ IFI) are decomposed from the strain amplitude dependent IF in transformation region. For practical application of shape memory alloys as a damping material, it is significant to evaluate the damping capacity by eliminating the influence of IFTr and consider its time independent real IF (IFPT+ IFI).

Relaxation and hysteresis internal friction in ultra-fine-grained copper at temperatures of up to 400°C

The temperature- and amplitude-dependent internal friction and elastic moduli of copper samples (99.95% Cu) subjected to deformation by equal channel angular pressing with a pass number of 1, 4, and 8 along the Bc route in the hertz range of loading frequencies at room temperature and temperatures of up to 400°C are investigated. The effect of deformation and subsequent recrystallization on the parameters of thermally activated internal friction peaks due to grain-boundary relaxation and the recrystallization of intensively deformed copper, and on amplitude-dependent internal friction due to dislocation hysteresis, is determined.