Internal Friction Measurements Research Articles

Intrinsic inhomogeneity in the electron-doped manganite Sr 0.95Ce 0.05MnO 3

Systematic studies of structural, magnetic, electronic, and elastic properties have been performed for the electron-doped manganite Sr 0.95Ce 0.05MnO 3. The results show that light doping with Ce in place of Sr in SrMnO 3 could stabilize the perovskite-type structure. The electronic transport and magnetism measurements show that the sample exhibits a charge ordering (CO) state below T CO ∼ 230 K , accompanied by softening of Young’s modulus due to a strong electron–phonon coupling. Cluster-glass behavior and the magnetoresistance (MR) effect are observed at low temperatures, resulting from the induced double-exchange (DE) ferromagnetic (FM) clusters embedded in the CO antiferromagnetic (AFM) matrix. Above T CO , the high temperature range appears to be dominated by local FM fluctuations, which is further supported by internal friction measurements. Our results indicate the existence of intrinsic magnetic inhomogeneity in electron-doped Sr 0.95Ce 0.05MnO 3.

Damping behavior of porous CuAlMn shape memory alloy

Internal friction measurements were conducted to examine the damping behavior of a porous Cu–11.9Al–2.5Mn (wt.%) shape memory alloy. It is found that the internal friction background significantly increased with increasing volume fraction or decreasing diameter of the pores due to stress concentration and mode conversion around pores when loaded, the refined microstructures and increased dislocation population.

Anelastic Relaxation due to Interstitial Solutes Diffusion in Nb and Nb-1 wt% Zr

Metals and alloys containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. The application of mechanical spectroscopy measurements to diffusion studies in body-centered cubic metals has been extensively used in the last decades. However the kind of preferential occupation of interstitial solutes in bodycentered cubic metals is still controversial. The anelastic properties of the Nb and Nb-1 wt% Zr polycrystalline alloys were determined by internal friction and oscillation frequency measurements using a torsion pendulum inverted performed between 300K and 650K, operating in a frequency oscillation in the hertz bandwidth. The interstitial diffusion coefficients of oxygen and nitrogen in Nb and Nb-1 wt% Zr samples were determined at two distinct conditions: (a) for low concentration of oxygen and (b) for high concentration of oxygen.

Interstitial Diffusion of Oxygen in Tantalum Obtained by Anelastic Relaxation Measurements

Anelastic relaxation measurements have been used in order to obtain information about several aspects of the behavior of solutes in metals, for example, matrix-solute interaction, interstitial diffusion, etc. The diffusion coefficient for interstitial solutes in body centered-cubic metals is accurately determined by anelastic relaxation measurements. The kind of preferential occupation of the interstitial solutes in body centered-cubic metals, such as oxygen and nitrogen in tantalum, is still controversial. Internal friction and frequency measurements as a function of temperature in tantalum sample were performed using a torsion pendulum operating in a frequency oscillation in the hertz bandwidth. These results presented the following phenomenon: the intensity of the internal friction peak decreased between the first run and the other runs. These results were decomposed, by the successive subtraction method, in elementary Debye peaks, for determination of characteristic anelastic relaxation parameters (relaxation strength, peak temperature, activation energy and relaxation time). Interstitial diffusion coefficients for oxygen in tantalum were determined, for different intensities of internal friction peaks, and when compared with literature, these results introduced a better adjustment for the tetrahedral preferential occupation sites of oxygen in tantalum.

Influence of Oxygen on the Damping Properties of Nb-Zr Alloys

Nb-1 wt% Zr polycrystalline and single crystalline samples were submitted to annealing, at pressure of 2.5 x 10-8 Torr and subsequently annealed in an oxygen atmosphere for three hours, in a temperature of 1170 K in oxygen at partial pressure of 5 x 10-5 Torr. Internal friction measurements as a function of temperature were performed between 300 K and 650 K, using a torsion pendulum inverted Kê-type operating in a frequency oscillation in the hertz bandwidth. Three internal friction peaks, which were assigned as Nb-O, Zr-O and Nb-N peaks were observed in oxidized single crystal sample and the relaxation parameters of the three peaks were obtained.

Anelastic Properties of Mg+3vol.%Gr Prepared by Ball Milling

Internal friction in ultra-fine grained Mg with 3vol% of Graphite was measured by forced vibration method at low frequencies of 0.1, 0.5, 1.0, and 2.0 Hz over a temperature range from room temperature to 753 K with continuous heating. The specimens were prepared by milling procedure in an inert atmosphere and subsequent compacted and hot extruded. Two developed peaks in the internal friction spectrum were obtained at temperatures ≈ 350 K and ≈ 550 K. While the position of the first peak is frequency dependent, the second peak position is stable, independent of measuring frequency. The activation energy of the low temperature peak was estimated. In the light of internal friction measurements, the high temperature internal friction peak is attributed to the generation and motion of dislocations produced by the difference in the coefficient of thermal expansion between the Mg matrix and Gr phase at the matrix–particle interfaces.

Slip planes and kink properties of screw dislocations in high-purity niobium‡

Temperature and strain-rate dependence of the flow stress of cyclically pre-deformed high-purity niobium single crystals have been measured in the temperature range 120,K ≤T≤350 ,K with high accuracy and reproducibility for five or more resolved shear-strain rates between 6.5×10-5 ,s-1 and 3.5×10-3 ,s-1. The data are quantitatively interpreted in terms of kink-pair generation and kink diffusion in a 0⟨111⟩/ 2 screw dislocations (a 0= cubic lattice parameter). The prediction of a discontinuity in the stress dependence of the activation volume (occasionally dubbed ‘the hump’) at a strain-rate-independent effective flow stress has been verified. From the stress dependence of the activation volume and from the magnitude of the discontinuity the spatial period of the Peierls barriers of the screw dislocations could be derived without having to assume a special shape of the Peierls potential. In the temperature range investigated, the measured periodicity is in quantitative agreement with {112} as elementary slip planes (i.e. the slip planes of the screw dislocations between cross-slip events) but incompatible with predominant slip on {110} planes. Examples of further quantitative results are for the effective stress at the ‘upper bend’ of the flow-stress–temperature relationship, the enthalpy of formation of a pair of isolated kinks, 2H k=(0.68 ±0.02),eV, and the activation energy of kink diffusion, . In agreement with the above-mentioned prediction, the same H k values are obtained above and below . The Nb data are compared with those for Ta, Mo, W, and α-Fe, which all exhibit a similar pattern. The comparison with the internal-friction measurements of D'Anna and Benoit shows very clearly that the classical γ-relaxation of Nb – called irreversible by D'Anna and Benoit – is caused by the thermally activated generation of kink pairs in a 0⟨111⟩/ 2 screw dislocations on {112} planes. For the reversible γ-relaxation two alternative mechanisms are discussed. The one based on kink-pair formation in screw dislocations on {110} planes appears to be the more likely one. This interpretation implies that the reversible γ-relaxation is identical with the β-relaxation and thus substantiates Chambers' claim of the intrinsic nature of the β-relaxation. ‡Dedicated to Professor Frank Reginald Nunes Nabarro on the occasion of his 90th birthday on March 7th, 2006.

Amplitude-dependent damping of PSZ with sinter defects

Samples of 3Y-PSZ (with yttria partially stabilized zirconia) ceramics were produced in a form of rectangular bar by uniaxial pressing with subsequent sintering and grinding. In some samples crack-type defects were induced under the larger surfaces by green-body pressing with very high pressure. The strain amplitude-dependent damping of these samples was measured in a single cantilever arrangement as the logarithmic decrement of free decaying bending vibrations. An increase of damping with strain amplitude was found. Compared to the samples without induced defects the samples with induced defects showed higher damping for all strain amplitudes and their damping increases strongly with increasing strain amplitude. Moreover, in the samples with induced defects, the damping for bending vibrations perpendicular to the defect-affected surfaces is much lower than parallel to those. Damping of the samples could be increased by bending fatigue performed in the apparatus by which the damping was measured. After a heat treatment up to 300 °C a decrease of damping was found which could possibly indicate healing of cracks. The results demonstrate that the measurement of internal friction is a powerful tool for detection of typical flaws such as pressing or sintering defects or cracks and can be used for non-destructive testing of ceramics.

Diffusion processes in Cu–Al–Ni shape memory alloys studied by mechanical spectroscopy and in situ transmission electron microscopy at high temperatures

We have studied the mobility of defects in the frozen β phase of the Cu–Al–Ni shape memory alloys by mechanical spectroscopy as a function of temperature. In parallel, we have characterized the microstructure and their evolution with over-heating treatments. Thermal treatments have been performed in situ in a transmission electron microscope by using a heating stage. Internal friction and modulus defect measurements have been correlated with the microstructural observations by transmission electron microscopy. We discuss the behavior of the internal friction spectra, corresponding to over-heating in the β-phase, and propose microscopic mechanisms responsible for the evolution when the material is not in thermal equilibrium. In particular, the dislocations became mobile in the temperature range between 750 and 800 K where the L2 1 atomic order changes to the B2 order. A relaxation peak has been observed in the equilibrium β phase domain, which has been examined in detail by isothermal measurements as a function of frequency. The activation enthalpy of the peak has been determined to be 3.05 ± 0.1 eV, and possible microscopic mechanisms responsible for the peak are discussed.

Internal friction of amorphous and nanocrystalline silicon at low temperatures

We measured the low temperature internal friction of a variety of hydrogenated amorphous, nanocrystalline, polycrystalline, and epitaxial silicon thin films. Most of the films studied are prepared either by hot-wire chemical-vapor deposition (HWCVD) or by plasma-enhanced chemical-vapor deposition (PECVD). We show that structural changes with varying modes of deposition can be monitored by the internal friction measurements, which are a sensitive probe to structural disorder resulted from atomic tunneling states below 10 K. For hydrogenated amorphous silicon films, the measurements are also sensitive to the content of atomic hydrogen and bulk molecular hydrogen trapped in the films. With H 2 dilution of the silane during deposition, a transition from amorphous to nanocrystalline phase takes place as H 2 dilution increases. We show that with increasing volume of nanocrystallinity, the internal friction increases in contrast to our common expectation. The results suggest a large structural disorder in the nanocrystalline phase that is at least comparable to that of amorphous phase exists. The observation of internal friction peaks in amorphous HWCVD films and in nanocrystalline PECVD films indicates that the microstructures of the HWCVD and PECVD films are different.

High-Temperature Mechanical Relaxations in Metals and Metallic Alloys

In spite of numerous works, the relaxation phenomena observed at high temperature (between room temperature and the melting temperature TM) are still under discussion. Because relaxation peaks were observed in single crystals, it is generally considered that the basis of the relaxation mechanism is linked to the dislocation network. The main difficulty for high temperature damping measurements is the great sensitivity of internal friction with several experimental parameters: the heating/cooling rate, maximal applied strain amplitude, sample purity, thermomechanical history of the sample, microstructure, etc. This sensitivity can explain the large scatter in experimental results published by various authors. Moreover, internal friction (IF) measurements performed during continuous heating or cooling and using an apparatus working at a quasi-static frequency, do not allow to completely describe the relaxation phenomena. On the contrary, isothermal mechanical spectroscopy (measurements of internal friction in a large frequency, temperature and maximal strain amplitude ranges) improves the experiments or evidences new relaxation effects. This is illustrated in this paper for various examples: slightly cold worked single crystals, polycrystals after a large cold work and recrystallization, non thermally activated peaks observed in metallic alloys, and relaxation peaks at very high temperature (above 0.9 TM).

Comparing Irreversible and Reversible Structural Relaxation in Bulk and Ribbon Metallic Glasses Zr<sub>52.5</sub>Ti<sub>5</sub>Cu<sub>17.9</sub>Ni<sub>14.6</sub>Al<sub>10</sub> and Pd40Cu30Ni10P20 by Mechanical Spectroscopy

By means of the vibrating reed technique, measurements of internal friction have been performed in the temperature range of 120 K < T < Tg (= glass temperature) on two amorphous alloys, each produced as ribbon and bulk material. The different contents of free volume result in an only slight shift of the onset of irreversible structural relaxation to lower temperatures (i.e., lower activation energies) for the ribbons, while considerably different amounts of structural relaxation occur. After correcting for the thermoelastic effect, the reversible structural relaxation, i.e., an approximately exponential increase of damping with rising temperature, is well described by KWW kinetics (β ≈ 0.3). For the Zr-based alloy only, a clear relaxation peak occurs in the range from 270 K to 320 K (for the first flexural vibration mode between 100 Hz and 400 Hz) induced by hydrogenation. In addition, the effect of plastic deformation on the damping behavior by cold rolling of the bulk materials has been examined.

Influence of Al concentration on the short-range and long-range diffusion of carbon in Fe–Al alloys

Internal friction measurements have been performed with Fe–Al alloys in the temperature range of 100–960 K by the vibrating-reed technique. The concentration of Al was varied between 0 (pure iron) and 50 at.% Al (FeAl) to analyze the effect of Al. Four damping peaks have been observed. From the Snoek-type peak, the parameters of the short-range diffusion of carbon in Fe–Al alloys have been determined, while the isothermal annealing at temperatures near the Snoek-type peak has yielded information about the long-range diffusion during precipitation of carbides.

Mechanical and dielectric investigation on point defects and phase transition in ferroelectric ceramics

Mechanical and dielectric measurements were used to investigate the behavior of point defects and phase transition in ferroelectric ceramics. Some interesting results were obtained: (1) the dielectric loss peak in La-doped Bi 4Ti 3O 12 was explained by the hopping of oxygen vacancies, the optimum doping content of La = 0.75 (Bi 3.25La 0.75Ti 3O 12) was discussed in terms of the competition between the density of oxygen vacancies and activation energies; (2) by use of internal friction measurements, the interaction between oxygen vacancies and ferroelectric domain walls was detected, the relationship between domain wall morphology and fatigue behavior was then well explained; (3) some internal friction peaks were also detected in SrBi 2Ta 2O 9 and Pr(Zr 0.52Ti 0.48)O 3 ceramics. The results mentioned above indicate that both mechanical and dielectric techniques are useful to clarify the mechanisms of ferroelectric behavior.

Damping behavior of physical vapor-deposited TiN coatings on AISI 304 stainless steel and adhesion determinations

Internal friction and elastic modulus measurements were carried out on AISI 304 stainless steel coated by physical vapor-deposited TiN, using a torsion pendulum and a vibrant-reed instrument. Some experiments showed several internal friction peaks, which are attributed to dislocation relaxation and to martensitic transformation from γ to α′. The materials were characterized by means of X-ray diffraction and scanning electron microscopy. Two new methods are proposed to determine the adhesion energy by internal friction in thin films layered materials: for the first it is necessary to determine the enthalpy by means of isochronal internal friction measurements, while for the second it is necessary to perform isothermal measurements.

Zener relaxation in manganites?

We conducted internal friction (IF) and elastic modulus measurements on several manganites in the temperature range 100–500 K. The La 1− x Ca x MnO 3 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 400 K, respectively. Both, peaks associated to relaxations, present activation enthalpies of 2–3 and 3–6 eV, whose intensity depends on x. In this work we associate the 400 K IF peak to a Zener relaxation of the cations that occupied the same crystallographic site. We believe that the 320 K IF peak is due to different crystalline states of the samples.

Interstitial oxygen mobility in superconducting samples ofBi2Sr2CaCu2O8+y

Since high-temperature superconductors were discovered, several studies havebeen made on their physical properties, attempting to associate them tothe origin of superconductivity. Obviously, the oxygen atoms interstitiallydissolved in the matrix have an important role in superconductivity, since theymove easily in the lattice. In addition, they contribute to hole creation in theCuO2 planes. Anelastic spectroscopy (internal friction) measurements are sensitive tools forthe study of defects in solids, in particular for oxygen mobility. In this paper,Bi2Sr2CaCu2O8+y samples with several different amounts of interstitial oxygen were analysed by means ofanelastic spectroscopy measurements. The measurements were performed by using a torsionpendulum operating at a frequency of about 40 Hz. Complex relaxation structures wereobserved and attributed to the shift of the oxygen interstitial atoms in BiO chains.

Reverse transformation behavior of a prestrained MnCu alloy

Prestrained thermoelastic martensite alloys have the characteristics of increased reverse transformation temperature and increased transformation heat by cold deformation. In this study, calorimetric analysis and internal friction (IF) measurements were applied to investigate the reverse phase transformation of a Mn–15at.% Cu alloy with prestrains up to 18%. The reverse phase transformation temperature increased along with a very small variation in transformation heat with an increase in prestrain. Meanwhile, the IF peak corresponding to the reverse phase transformation increased with prestrain up to 4%, then decreased with an increase in prestrain. Twin boundary reorientation and de-twinning occurred in the prestrained specimens, and the change in the fraction of 90° twin boundaries by the prestrain was similar to that of the reverse phase transformation IF. Based on the stress-induced nucleation model for transformation, the change in the reverse transformation IF by the prestrain could be simulated as a function of both the prestrain and vibration frequency. The twin boundary reorientation and de-twinning caused by the prestrain are thought to influence the reverse phase transformation behavior by affecting the features of the boundaries that are the possible nucleation sites for reverse transformation.

Improving Heat Resistance of Silicon Nitride Ceramics with Rare-Earth Silicon Oxynitride

Heat resistant silicon nitride ceramics sintered with RE2O3 (RE: Sc, Y, and lanthanide) and those with RE2Si2O7 as grain boundary phase were briefly reviewed. High-temperature strength and internal friction of silicon nitride ceramics with sintering additive of RE4Si2O7N2 composition (RE: La, Lu, Sc, and Yb) were measured to select candidates for evaluation of creep resistance. Following the results of high-temperature strength test and internal friction measurement, Yb and Lu were selected for sintering additive systems. Si3N4 powder with 2.4 mol% Yb4Si2O7N2 were gas-pressure hot-pressed at 1800°C for 1 h under 20 MPa in 1 MPa N2 (YB). Si3N4 powder with 1.2 mol% (LU12) and 4.8 mol% (LU48) of Lu2O3 were gas-pressure hot-pressed at 1950°C for 1 h under 20 MPa in 1 MPa N2. High temperature strength of LU12 was at its maximum among the three ceramics. Stress-strain curve of YB was linear at 1200°C, but at 1400°C it was non-linear. The Stress-strain curve of LU48 was non-linear at 1500°C. For LU12 the stress-strain curve was linear, and it was linear even at 1600°C, indicating that LU12 broke as a brittle fracture at 1600°C. LU12 had excellent oxidation resistance, and weight gain during the oxidation at 1500°C for 1000 h was 4 g/m2. Creep resistance of LU48 was higher than that of YB. Creep life time of LU12 at 1500°C under tensile stress of 137 MPa exceeded 1678.5 h. Time-to-failure of LU12 was strongly stress sensitive.

Characterization of the Interaction of the Interstitial Atoms with the Substitutional Atoms and with the Dislocations in Extra-Mild Steels through Coupled Use of Thermoelectric Power and Internal Friction Measurements

In Fe-C-Mn steels, the carbon atoms in solution can be either completely free in the iron matrix or in interaction with manganese atoms. In this context, a methodology based on the combined use of thermoelectric power and internal friction measurements was developed in order to evaluate quantitatively these two populations of carbon atoms. This methodology was used to determine the binding energy of the C-Mn dipoles and to follow the precipitation kinetics of the two populations of carbon atoms and/or their segregation kinetics to the dislocations during an isothermal treatment. Lastly, the influence of each population of carbon atoms on the strain aging of extra-mild steels was discussed.