Low Frequency Internal Friction Measurements Research Articles

Effect of Purity on Dislocation-Induced Relaxations in Molybdenum Single Crystals

Dislocation-induced relaxations in different molybdenum single crystals were investigated by means of low-frequency internal friction measurements in the temperature range of 20–600 K. The results indicated that the appearance of the dislocation-induced relaxations strongly depends on the purity of the molybdenum, although the intrinsic dislocation relaxations appeared at about 100 K and 450 K in the high-purity molybdenum. The molybdenum containing a small amount of carbon did not exhibit the intrinsic dislocation relaxations but rather revealed a modulus increase due to the dislocation pinning caused by the dissolved carbon. When the molybdenum containing a small amount of carbon was annealed up to 700 K, a new relaxation peak appeared at about 450 K. The activation process for this relaxation indicated that it could be attributed to the relaxation due to a carbon-dislocation interaction. In addition, it was shown that the dislocation-induced relaxations in medium-purity molybdenum were small, which was attributed to the residual substitutional impurities in the molybdenum.

Dislocation relaxation and alloy softening of bcc alloys

Recently, low-frequency internal friction measurements on a series of Fe–Cr alloys by Konstantinović and Terentyev [M.J. Konstantinović and D. Terentyev, Mater. Sci. Eng. A 521–522 (2009) p.106] have demonstrated that increasing Cr concentrations lead to an increase in the strength of the β-relaxation at the cost of the γ-relaxation (Chambers’ notation). In the same concentration and temperature regime, the alloys show alloy softening. It is argued that both phenomena are due to the same process, namely the influence of foreign atoms on the transformation of the cores of a 0⟨1 1 1⟩/2 screw dislocations from their low-temperature configuration, capable of forming kink pairs on {1 1 0} planes, to their high-temperature configuration with kink-pair generation on {2 1 1} planes.

Dislocation relaxation and alloy softening of bcc alloys

Recently, low-frequency internal friction measurements on a series of Fe–Cr alloys by Konstantinovic and Terentyev [M.J. Konstantinovic and D. Terentyev, Mater. Sci. Eng. A 521–522 (2009) p.106] have demonstrated that increasing Cr concentrations lead to an increase in the strength of the β-relaxation at the cost of the γ-relaxation (Chambers’ notation). In the same concentration and temperature regime, the alloys show alloy softening. It is argued that both phenomena are due to the same process, namely the influence of foreign atoms on the transformation of the cores of a 0⟨1 1 1⟩/2 screw dislocations from their low-temperature configuration, capable of forming kink pairs on {1 1 0} planes, to their high-temperature configuration with kink-pair generation on {2 1 1} planes.

Low-frequency losses in silica glass at low temperature

Precise low-frequency internal friction measurements on vitreous silica, taken over a wide temperature ( 4 K < T < 300 K) and frequency range (40 Hz < ν < 14 kHz), show remarkable similarities, but also suggestive differences with recent light-scattering experiments. In the interval 30 K < T < 110 K, the exponent α ( T ) of the power-law relaxational spectrum at low frequencies turns out to be proportional to T − T k , with a minimum at around T k = 13 K. This phenomenon is interpreted as a manifestation of quenched spatial disorder.

The low frequency internal friction and electric magnetic properties in La0.7Pb0.3MnO3 bulk materials

Abstract The polycrystalline samples of La 0.7 Pb 0.3 MnO 3 synthesized by the sol–gel method were studied by the low frequency internal friction measurements and the resistance and ac susceptibility measurements. There are two internal friction peaks at 258 and 198 K, respectively, the peak positions of which do not shift with frequency but the peak heights of which decrease with increasing frequencies. The modulus softening is evident at the corresponding temperatures. Corresponding to the two internal friction peaks, there are two resistance peaks, and a sharp rise and a following continuous decrease of ac susceptibility. It is suggested that the high temperature peaks correspond to the paramagnetic (PM) to ferromagnetic (FM) transition, while the low temperature peaks originate from the process of an anti-ferromagnetic phase (AFM) separating from the ferromagnetic matrix (phase separation) in polycrystalline materials. The peak positions of internal friction and resistance will move towards higher temperature when the sample was annealed in flowing oxygen, and the low temperature peaks become smaller.

Damping mechanism in the novel La 2Mo 2O 9-based oxide-ion conductors

In this paper, the microscopic diffusion mechanism of oxygen vacancies in the oxygen-ion conductors La 2− x A x Mo 2O 9 with A=Bi, K and x=0–0.15 are studied by the low frequency internal friction measurements. An internal friction peak associated with the phase transition around 833 K and two relaxation peaks associated with the short-distance diffusion of oxygen vacancies were observed in all samples. With increasing K and Bi doping contents, the activation energies of both relaxation peaks increase; the high-temperature peak decreases in height while the other relaxation peak increases. The phase transition can be completely suppressed by 10% K or 15% Bi doping. It is found that the effect of K-doping is stronger than that of Bi-doping. Combining with the analysis of the crystal structure of La 2Mo 2O 9, the microscopic mechanism of oxygen vacancy diffusion for the two relaxation peaks are suggested.

Internal friction of powder metallurgy (P/M) and ingot metallurgy (I/M) Al-Fe alloys at elevated temperature

Low-frequency internal friction measurements have been carried out on the powder metallurgy (P/M) and ingot metallurgy (I/M) Al–Fe alloy. Internal friction peaks can be seen at about 820–830 K and 530–620 K in the I/M alloys, but not in the P/M alloys. The former is probably due to the grain-boundary relaxation and the latter to recrystallization. Activation energies for the grain-boundary relaxation are estimated to be in two ranges: one is between 100 and 130 kJ mol−1 and the other is between 200 and 210 kJ mol−1, according to the iron content and fabrication processes. The high activation energy is given by the low iron content I/M alloys having a bamboo-like grain. It is suggested that such a difference in the activation energy is due to whether or not the solute iron diffuses into the grain boundary to lower the grain boundary energy.

Anisotropy of the Anelastic Relaxation Associated with Interstitial Carbon in Nickel

The behaviour of interstitial C atoms in Ni has been studied by low-frequency internal friction measurements using single crystal specimens. The magnitude of the relaxation peak, which appears at 520 K for f= 1 Hz, is the largest when the axis of shear stress is , while the peak is virtually absent when the stress axis is . This behaviour can be accounted for by considering pairs of C atoms occupying the 2nd neighbour octahedral sites. The kinetics of the relaxation is discussed by assuming the relaxation is due to the reorientation of the 2nd neighbour pairs through the 3rd neighbour configuration.

Low-Temperature Mechanical Loss Spectroscopy of 5N Lead

By internal friction measurements in 5N lead, a relaxation peak is observed in the vicinity of 40 K at a frequency of 250 Hz, and in the vicinity of 150 K at a frequency of 18 MHz (ultrasonic attenuation). This thermally activated relaxation demonstrates all the characteristics of a Bordoni peak. Using the ultrasonic low-frequency coupling method, new high-temperature signatures were observed on each temperature side of the high frequency Bordoni peak (150 K). These signatures can only be interpreted if one assumes that a thermally activated kink pair formation (KPF) mechanism is responsible for the high-frequency Bordoni peak. Low-frequency internal friction measurements performed after low-temperature plastic deformation have shown that a modulus softening effect, similar to the softening already observed in aluminium after plastic deformation or after electron irradiation, occurs in lead. This result confirms the existence of the dislocation lubrication process recently proposed to explain the discrepancy between the low-temperature behaviour of the critical resolved shear stress in FCC metals and mechanical spectroscopy measurements, and the signatures observed at very low temperatures suggest that a short-circuited KPF mechanism is responsible for this lubrication process.

High Temperature Properties of TiCN-Mo2C-Co Cermets Studied by Mechanical Spectroscopy

Low frequency internal friction measurements were performed on TiC 0.7 N 0.3 -MO 2 C-Co cermets in an inverted torsion-pendulum working with forced oscillations. A thermally activated high temperature background and three thermally activated peaks were observed in the internal friction spectra. Two peaks, which are stable during thermal treatments, appear (at I Hz) at about 1050 K and 1200 K respectively. The third peak, appearing at about 950 K, is only observed during the first heating of the as-received samples. In order to locate the relaxation phenomena, similar measurements were performed on carbide-carbonitride skeletons, in which the metallic binder phase was chemically removed. Complementary microstructural characterizations, performed by conventional TEM, allow one to identify the physical mechanisms responsible for the IF peaks and background.

Internal Friction Peak in Cold-Worked "Pure" Aluminum and Aluminum Alloys

Low frequency internal friction measurements have been made on pure aluminum and dilute aluminum alloys in heavily cold-worked states. A relaxation peak is observed at about 200 K(for 1Hz) even in specimens of nominally 4N or higher purity. This peak is considered to be the same as those previously reported by several researchers for dilute aluminum alloys of Cu, Mg or Ga. Among various elements so far examined (Cu, Si, Fe, Ge, Mg), Si has a dominant effect. The anomalous features of the peak, i.e. high activation energy and small preexponential factor for the relaxation time can be understood in terms of a model in which the anelastic elements exhibit strong interaction .

Mechanical relaxation due to hydrogen—solute complexes in dilute Ni-Ti-H alloys

Dilute nickel alloys charged with hydrogen are known to exhibit an internal friction peak, which is attributed to the reorientation of hydrogen—solute atom pairs. In order to determine the geometrical configuration of the pair, we have studied anisotropy of the relaxation strength in dilute Ni-Ti-H alloy single crystals by low-frequency internal friction measurements. The orientation dependence of the peak height suggests that the defect symmetry is 〈111〉 trigonal. One of the possible configurations is the Ti-H pair in which hydrogen occupies the second neighbour octahedral sites around the substitutional solute atom. The peak has been found to be suppressed by an external magnetic field, indicating that magneto-elastic effects play an important role.

Internal friction due to twinning dislocations in Cu-Ge solid solution alloys

Anelastic behaviour of Cu-Ge solid solution alloys has been studied by low frequency internal friction measurements. Plastic deformation gives rise to characteristic internal friction in the temperature range between 80 K and 350 K, which is attributed to the motion of twinning dislocations. By using single-crystal specimens of a Cu-8%Ge alloy, the dependence of the magnitude of the internal friction on the crystal orientation and the degree of deformation has been examined. The results suggest that the internal friction is due to local oscillatory motion of individual twinning dislocations. The internal friction is suppressed completely by electron irradiation, which can be explained in terms of pinning of the dislocations by point defects.

Observation of the Glass Transition of Metallic Glasses by Low-Frequency Internal Friction Measurements with a Collette Pendulum

Observation of the Glass Transition of Metallic Glasses by Low-Frequency Internal Friction Measurements with a Collette Pendulum

Pseudoelastic and anelastic effects due to the motion of twin boundaries in copper-based alloys

Copper alloys, e.g. with a few at.% of Ge, are known to deform by slip and twinning when subjected to a tensile test at room temperature. Such alloys exhibit a large hysteresis loop or pseudoelasticity in a loading-unloading cycle, which is believed to be due to reversible motion of twin boundaries. The mobility and the annealing behaviour of twinning dislocations in several copper alloys with Ge, Si or Al have been studied by low-frequency internal friction measurements, electrical resistivity measurements and electron microscopy. Deformed samples show a characteristic anelastic effect; internal friction increases linearly with temperature in the range from 80 to 280 K and falls down rapidly above room temperature. The magnitude of the anelastic effect depends on the solute concentration and on the degree of deformation similarly to that of the pseudoelastic effect. The internal friction is tentatively explained as arising either from l ocal motion of twinning dislocations or from rearrangement of metastable stacking sequences.

The crystallization of a Pd 60Ti 20Si 20 metallic glass

The kinetics and mechanism of crystallization have been followed in a Pd 60Ti 20Si 20 metallic glass by means of a combination of experimental techniques. As quenched alloys contain a variable population of crystals and/or nuclei. Oxide islands were found mostly on the dull (wheel-side) surface of the ribbon, favouring partial crystallization around 710 K. The glass transition temperature, T g , is manifest in DSC and low-frequency internal friction measurements from heating rates of 1 K/min upwards, prior to the main crystallization event (761 and 772 K at 20 K/min heating rate, respectively). Isothermal crystallization in the temperature range from 739.0 to 758.7 K occurred in two steps because of a different population of quenched-in nuclei in various parts of the ribbon. A Johnson-Mehl-Avrami analysis of the DSC isothermal output gave an Avrami exponent of 3, indicating growth on preexisting nuclei, as shown by microscopy observations. The activation energy and the preexponential factor for growth are very high: 566 ± 20 kJ/mol and 10 36ms −1 respectively. This finding is discussed with reference to analogous data for diffusion in metallic glasses.

The dynamical response of dislocation structures introduced by twisting deformation of high purity aluminium single crystals

The dynamical response of dislocation structures introduced by various types of deformation was studied with low frequency internal friction measurements. A strong internal friction peak situated around 310°C was observed. It is shown that the peak is associated with the dynamical response of dislocation structures introduced by twisting deformation. Such dislocation structures are stable at high temperatures and therefore correspond to a minimum energy state. Tensile deformation reduces this peak which has an activation energy of about 2 eV. The non-elastic strain component during relaxation is produced by dislocation slip, but the relaxation rate is controlled by the non-conservative shift of the nodes of the dislocation networks. The dislocation configurations produced by different types of deformation were studied with the help of X-ray Laue spot analysis and transmission electron microscopy observations. A phenomenological theory based on elastoplasticity is proposed.

Determination of the glass transition temperature of metallic glasses by low-frequency internal friction measurements

Based on the “isoviscous” definition of the glass transition (η(Tg) = 1012 Ns/m2), it is shown that the glass transition temperature Tg can be determined by low-frequency internal friction measurements. By comparing the anelastic and viscoelastic contributions to internal friction, an upper frequency limit for this kind of Tg determination is derived; for metallic glasses, a rough estimate of 0.2 Hz is given. In corresponding experiments at 0.1 Hz on amorphous Pd40Ni40P20, a cross-over of the internal friction Q−1 vs temperature is observed for different heating rates Ṫ: whereas below the glass transition range Q−1 is lower for lower Ṫ due to structural relaxation, the opposite is true for higher temperatures due to the shift in Tg with Ṫ. This shift is found to be linear in log Ṫ both for Tg values obtained by internal friction and by DSC. However, a single straight line of Tg (log Ṫ) for both methods is obtained from 0.03 to 100 K/min only if in DSC Tg is defined at the end of the corresponding increase in specific heat. These findings are discussed with respect to the compatibility of the different definitions of Tg. There seems to be some independent evidence that the results obtained on Pd40Ni40P20 might be of more general importance.

Ultrasonic response of dilute AlFe alloys irradiated with 2.5-MeV electrons.

Ultrasonic attenuation and velocity measurements were made as a function of polarization, temperature, frequency, and annealing before and after 2.5-MeV electron irradiation of dilute AlFe alloys. In addition to the relaxation peaks observed in earlier low-frequency internal-friction measurements, two new relaxation peaks were found. One of these has all the properties predicted by a size-effect model. The peak structure observed is very different from that found for AlMn, suggesting that theories based only on impurity size require extension. 20 references, 12 figures, 3 tables.

The effect of hydrogen solubility on the internal friction of VTi alloys

The purpose of this note is to present results of low frequency internal friction measurements on three hydrogenated V-Ti alloys which illustrate how the internal friction spectrum changes from one dominated by hydride precipitation to one dominated by hydrogen in solution. Demonstrates how damping due to hydrogen changes in b.c.c. alloys as the hydrogen terminal solid solubility increases. Low solubility alloys exhibit a broad damping peak at temperatures that can be associated with hydride precipitation. As the hydrogen solubility increases, peaks due to hydride precipitation and hydrogen in solid solution can co-exist in the alloy, or as in the case for the V-10 at .% Ti alloy containing 2.3 at .% H, only the low temperature hydrogen damping will occur.