Relaxation Peak Of Internal Friction Research Articles

Studying the influence of substitutional elements on mechanical behavior of Alloy 718

In nickel-based superalloys, substitutional solute species have a strong impact on in service mechanical properties as well as on oxidation and corrosion resistances. In alloy 718, recent studies carried out by tensile tests highlighted the fact that refractory solute species are able to interact strongly with mobile dislocations during plastic deformation, generating dynamic strain ageing, and, in wide ranges of tests temperatures and strain rates, Portevin-Le Chatelier effect. The precise nature of the substitutional element responsible for such a dynamic interaction is still subject to debate. We addressed this question by means of mechanical spectroscopy studies of alloy 718 and various related alloys corresponding to monitored changes in the chemical composition. Only a single internal friction relaxation peak has been observed for all the studied alloys. By analyzing the damping behavior of these alloys at different imposed solicitation frequencies by sweeping a large temperatures range, the activation energies of the relaxation process and the type of mechanism involved have been determined. The process is a “Zener relaxation” in the alloys, i.e. a substitutional atoms dipole reorientation under applied stress. The results tend to prove that Niobium is not involved in the relaxation process whereas Molybdenum content seems to play an important role in the relaxation intensity.

Atomic relaxation processes in an intermetallic Ti–43Al–4Nb–1Mo–0.1B alloy studied by mechanical spectroscopy

An advanced intermetallic γ-TiAl-based alloy containing Nb and Mo has been studied to understand the microscopic mechanisms taking place during thermal treatments carried out to adjust a fine, nearly lamellar microstructure. The evolution of the microstructure has been characterized by high-energy X-ray diffraction and electron microscopy, while the atomistic mechanisms of defect mobility have been studied through internal friction and dynamic modulus measurements. An internal friction relaxation peak has been observed at about 1050K (for 1Hz) in the initial oversaturated α2-Ti3Al phase, whose intensity strongly decreases after precipitation of the γ-TiAl laths. The activation parameters of this relaxation have been measured, Hact=3.1±0.05eV, τ0=8.3×10−17s and β=1.3, and the relaxation is attributed to a point defect mechanism taking place inside the supersaturated α2-Ti3Al phase. A new Zener-like atomistic model based on stress-induced reorientation of Al–VTi–Al dipoles has been developed to explain the observed relaxation, resolving the controversy concerning the relaxation peak at 1050K present in many γ-TiAl-based alloys. Precipitation of the γ-lamellae has also been considered as being responsible for the dynamic modulus hardening and, additionally, for another contribution to the internal friction at higher temperature than the described relaxation. Finally, the theoretical Debye equations as a function of temperature, for both internal friction and dynamic modulus, have been applied, using the measured activation parameters, to perform a deconvolution of the relaxation and precipitation contributions. The obtained results agree well with the experimental ones at different frequencies, allowing a global interpretation of the involved atomic processes.

Oxygen Vacancy Relaxation in Ca<sub>3</sub>Co<sub>4</sub>O<sub>9+δ</sub> Ceramics

Ca3Co4O9+δceramic powders were synthesized by the polymerized complex (PC) method. The same Ca3Co4O9+δceramic bar were treated in turn with three different processes of oxygen treatment: with no treatment, with oxydol (H2O2) treatment, and with N2treatment. Dynamic mechanical analysis (DMA) was performed from 123 to 623 K at rate of 1 K/min while the measuring frequencies are 0.05, 0.1, 0.25, 0.5, 1, 2, and 5 Hz. Two internal friction peaks are observed: one at the temperature range from 360 to 400 K (a broad peak, peak 1) and the other at around 390 K (a sharp peak, peak 2). Peak 2 is in correspondence with sudden metal-semiconductor transition (MST) near 400 K. Peak 1 is a kind of internal friction relaxation peak. For the sample with H2O2treatment and with no treatment, the activation energyHare 1.24 eV and 1.04 eV, respectively, and the preexponential factor τ0are 2.54×10-17sec and 7.82×10-15sec, respectively. We speculate that the mechanical relaxation process occurs in the Ca2CoO3subsystem of Ca3Co4O9+δ. The relaxation process for sample with no treatment is associated with the migration of OVs clusters in Ca2CoO3subsystem, and the relaxation process for the sample with H2O2treatment is associated with the migration of isolated OVs in Ca2CoO3subsystem.

Effect of alloying with Mn and Co on the temperature dependence of internal friction in Fe-Ni-C invar alloys

Temperature dependences of internal friction (TDIF) have been studied by the method of resonance bending vibrations in a kilohertz frequency range in the temperature range from 100 to 900 K in fcc Fe-Ni-X and Fe-Ni-X-C (X = Mn, Co) alloys with a Ni content of about 30 wt %. To produce a single-phase austenitic structure, the alloys were homogenized at 1373 K in vacuum and rapidly cooled in oil. At temperatures of 550–587 K, above the Curie temperature of the alloys, in the TDIF curves there is observed a carbon relaxation peak of internal friction. It has been demonstrated that in the alloys studied the temperature of the peak Tmax at vibration frequencies of 1.5–2 kHz is more than 100 K higher than the Curie point TC and that the alloying elements Mn and Co increase the difference between Tmax and TC. The activation energy calculated within the framework of the Wert-Marx model is equal to 1.1 eV. It has been found out that the alloying of Fe-Ni-C with Mn induces a certain decrease in the temperature and intensity of the carbon peak, while addition of Co, on the contrary, leads to an increase in the peak temperature and intensity of damhing of elastic vibrations. The causes of such effect have been considered.

Effect of hydrogen on internal friction and elastic modulus in titanium alloys

The effect of hydrogen on the variation with temperature of internal friction ( Q − I ) and elastic modulus ( E) of a number of Ti-based alloys has been studied in the Hz and kHz frequency ranges. A relaxation peak of internal friction with a high degree of relaxation ( Q −I max ∼ 10 −1) and with a Δ E effect is observed in all hydrogen-doped samples at T ∼ 600 K at ∼1 kHz, and at T ∼ 500 K at ∼1 Hz. Such a peak is not present in samples without hydrogen. The activation energy W and the frequency factor v 0 of the observed relaxation are determined to be W ∼ 1.55 eV, v 0 ∼ 10 17 s −1. It is shown that the observed effects are connected with the mechanism of grain boundary relaxation, as the introduction of hydrogen into titanium alloys leads to the formation of fine-grained structures.

Structure and Anelasticity of Fe-Ge Alloys

Several ternary Fe – Ge - C alloys with Ge contents ranging between 3 and 27 at. % have been studied. The structure, anelastic, thermodynamic and kinetic phenomena in Fe - 3, - 12, - 19/21 and – 27 Ge have been examined by X-ray diffraction (XRD), heat flow (DSC), vibrating sample magnetometry (VSM), optical-light and scanning electron microscopy, and internal friction (IF) methods. The Fe - 3Ge and Fe - 12Ge alloys form b.c.c. solid solutions. A Snoek-type internal friction (P1) peak is recorded in the Fe - 3Ge alloy with parameters similar to those for α-Fe: Н = 0.86 eV, Δ = 0.015, β = 0.72 and τ0 = 2 × 10-15 s, showing that Ge atoms have little influence on the diffusivity of carbon in iron. The Fe - 12Ge alloy, with a Curie point around 1008 K, has several IF peaks: a broad Snoek-type (P1 and P2), the P3 peak caused by structural changes in as quenched specimens during annealing, and a P4 (Zener) peak at higher temperature (Tm ≈ 773 K at f = 2 Hz, β ≈ 0.7). The Fe - 21Ge alloy has bcc or bcc plus hexagonal structure depending on heat treatment. The structure of the Fe3Ge-type alloy (Fe - 27Ge) consists mainly of hexagonal phases, i.e. hexagonal ε (D019), β (B81), and cubic ε′ (L12), and exhibits corresponding magnetic ordering transitions below 873 K which are not well-reflected in the common Fe - Ge phase diagrams. In particular a high stability of the hexagonal ε phase at room temperature is noted. A broad internal friction relaxation peak with Δ = 0.0036, H ≈ 1.8 eV and τ 0 = 2 ⋅ 10-17 s is found in Fe – 27 Ge and is classified as a double Zener peak in the ε and β two-phase mixture.

Structure and anelasticity of Fe 3Ge alloy

The structure and anelastic properties of Fe-27 at.%Ge alloy are studied. Long-term annealing of the as-cast alloy at 1273 K leads to homogenising and several transformations take place below 873 K. These low temperature transitions are studied by several methods: X-ray diffraction, calorimetry, vibrating-sample magnetometry and internal friction, and are related to magnetic transitions in the different phases. A high stability of the hexagonal ɛ (D0 19) phase at room temperature is recorded. The hexagonal β (B8 1) phase is also detected in the alloy at room temperature, while the presence of the ɛ′ and α phases is doubtful. A broad internal friction relaxation peak with the relaxation strength of Δ = 0.0036, the activation energy of about 1.78 eV and the preexponential relaxation time of τ 0 = 2 × 10 −17 s was discovered and classified as the Zener peak in both the ɛ and β phases.

Migration and redistribution of oxygen vacancy in barium titanate ceramics

Degradation of barium titanate based multilayer capacitor mainly results from migration and redistribution of oxygen vacancy. For barium titanate ceramics, the authors observe an internal friction relaxation peak around 70°C due to oxygen vacancy, and its relaxation strength differs greatly for specimen aged at 85°C for 120h and at 150°C for 5h. Two possible explanations are proposed, one based on symmetry-conforming short-range order while the other on the interaction between oxygen vacancy and domain wall during aging process. In any case, relaxation thermodynamics is a powerful tool to investigate the migration and redistribution of oxygen vacancy in barium titanate ceramics.

A Study on the Low Temperature Internal Friction Relaxation Peak in a Ti<SUB>49.8</SUB>Ni<SUB>50.2</SUB> Alloy

The low temperature relaxation peak appearing around 200 K in Ti49:8Ni50:2 shape memory alloy is a multiple relaxation process with activation energy Q ¼ 0:39 eV and frequency factor f0 ¼ 6:2 � 10 9 s � 1 and is associated with the interaction of dislocations with pinning vacancies. Due to the increase of dislocation density and the annihilation of quenched-in vacancies after thermal cycling, the height of relaxation peak PR decreases with increasing the number of thermal cycling. Higher amounts of dislocation-vacancy reaction cause a higher relaxation damping under the condition of higher quenching temperature. The quenched-in vacancies can have a significant effect on the transformation rate, and thus the heights of transformation peaks PH1 and PC1 decrease with increasing quenching temperature. Dislocations introduced by both thermal cycling and quenching from high temperature will depress the martensitic transformation, and hence decrease the peak temperatures of PH1 and PC1.

Grain-Boundary Viscosity of BaO-Doped SiC

Internal friction characterization of the viscosity of a residual SiO2/BaO glass, segregated to grain boundaries of polycrystalline SiC, is presented. The anelastic relaxation peak of internal friction, arising from viscous slip along grain boundaries wetted by a glass phase, is analyzed. Two SiC polycrystals, containing SiO2/BaO glasses with different compositions, are studied and compared with a SiC polycrystal containing only pure SiO2. The internal friction peak is first analyzed with respect to its shift upon frequency change. This analysis allows quantitative assessment of both the intrinsic viscosity and the activation energy for viscous flow of the grain-boundary phase. Both parameters markedly decrease with increasing amounts of BaO dopant, which is consistent with data reported in the literature on SiO2 and SiO2/BaO bulk glasses with the same nominal composition. Analysis of the peak morphology is also attempted, considering the evolution of peak width while varying the grain-boundary glass composition. Moreover, the role of microstructural parameters, such as the distributions of grain size and grain-boundary angles, on the broadening of the internal friction peak is addressed, and a procedure is proposed that allows quantitative evaluation of the activation energy for viscous flow of intergranular glass merely from the width of the internal friction peak.

Local Viscosity of Si-O-C-N Nanoscale Amorphous Phases at Ceramic Grain Boundaries

Internal friction characterization has been used to quantitatively assess the viscosity characteristics of Si-O-C-N glasses segregated to nanometer-sized grain boundaries of polycrystalline Si3N4 and SiC ceramics. A relaxation peak of internal friction, which arises with rising temperature from the viscous sliding of glassy grain boundaries, was systematically collected and analyzed with respect to its shift upon changing the oscillation frequency. As a result of such an analysis, both activation energy for viscous grain-boundary flow and inherent viscosity of the intergranular glass film could be quantitatively evaluated. Two main features are shown: (i) the presence of N and/or C greatly affects the viscosity characteristics of SiO2 phases at Si3N4 and SiC grain boundaries; and (ii) the internal friction method has potential as a unique experimental tool for understanding the local properties of nanoscale amorphous phases in new ceramic materials.

Aging effect on the low temperature internal friction relaxation peak in a Ti 49Ni 51 alloy

The internal friction relaxation peak appearing around 200 K in TiNi alloys is associated with the interaction of twin-related dislocations with the pinning agents. The 200 K relaxation peak in the 400 °C aged Ti 49Ni 51 alloy appears at the R-phase and martensite but not at the B2 phase, since there is no twin-dislocation available in the latter. The sources of the pinning agents are due to the quenched-in vacancies or Ti 11Ni 14 precipitate-vacated lattice sites in the matrix. It is found that 400 °C aging will significantly affect the relaxation characteristic in Ti 49Ni 51 alloy. These aging effects on the 200 K relaxation peak in Ti 49Ni 51 alloy will be systematically investigated in this study.

Internal Friction Analysis of CaO-Doped Silicon Carbides

Internal friction originated from sliding and diffusional flow along grain boundaries was monitored (as a function of both temperature and damping frequency) in model SiC polycrystals with an intergranular SiO2 glassy film. Emphasis was placed on the change of the internal friction characteristics upon additional Ca cation. It is expected that Ca cation segregates to the intergranular glass phase and modifies its network structure. The presence of a relaxation peak of internal friction due to grain-boundary sliding enabled quantitative evaluation of the activation energy for viscous flow of the intergranular glass and the related viscosity magnitude. A peak-analysis procedure, according to the peak-shift method (i.e., monitoring peak shift upon damping frequency change), is proposed, which quantitatively revealed the activation energy for viscous flow in various impurity-doped intergranular glasses. The presence of chemical gradients at grain boundaries, namely the presence of families of boundaries within the SiC polycrystal with different chemical characteristics, has also been analyzed by taking into account the dependence of peak morphology on damping frequency.

The decay of low-frequency elastic oscillations in a Ba2NaNb5O15 crystal

The internal friction and shear modulus of a barium sodium niobate crystal were studied using the torsion pendulum technique at a frequency of ∼25 Hz in the temperature range from 80 to 800 K. An internal friction relaxation peak of the domain nature was observed at 228 K. A relaxation process responsible for this internal friction peak is explained through compensation of the electric charge (induced by a piezoelectric effect at the 180° domain walls) by charged point defects diffusing toward the domain walls.

Chemistry and inherent viscosity of glasses segregated at grain boundaries of silicon nitride and silicon carbide ceramics

Electron microscopy/microanalysis and internal friction characterizations have been concurrently used to quantitatively assess both the morphology/chemistry and the inherent viscosity of residual high-SiO 2 glasses segregated to grain boundaries of polycrystalline Si 3N 4 and SiC ceramics. The anelastic relaxation peak of internal friction, arising from the viscous slip along grain boundaries wetted by glass, was collected in a plot of internal friction vs temperature. The peak was analyzed with respect to its shift upon changing the oscillation frequency, in order to assess the inherent viscosity of the intergranular glass film. From the internal friction analysis and the precise information of both thickness and chemistry of the grain-boundary film obtained by electron microscopy, a quantitative determination of the inter granular viscosity and the activation energy for viscous flow was attempted. The viscosity of intergranular high-SiO 2 glasses as a function of temperature is compared to the literature data for bulk SiO 2 glass and discussed in terms of the respective anion structure of the glass.

The mechanism of low frequency internal friction in concentrated Cu-Al and Cu-Zn alloys

Abstract The present paper attempts to give a detailed theoretical analysis of the mechanism for a relaxation peak of internal friction which occurs around 210K in concentrated Cu-Al and Cu-Zn alloys at about 1 Hz. It is shown that the observed peak is a superposition of two components, which are respectively induced by the overall motion of extended dislocations (acoustical mode) and the relative motion between two partials (optical mode). Assuming that the solute atom-vacancy pairs on dislocation lines act as mobile pinning agents damping the motion of dislocations, the evaluated peak temperature is close to the observed one.

Effect of Aging on Yttria‐Stabilized Zirconia: III. A Study of the Effect of Local Structures on Conductivity

Changes in local structures with aging in yttria‐stabilized zirconia were examined by extended x‐ray absorption fine structure (EXAFS) and internal friction measurement. An analysis of EXAFS shows that a decrease in the first nearest neighbor coordination number of Zr ions, which means short range ordering of oxygen ion vacancies, a decrease in distance between a Zr ion and its first nearest atoms, and an increase in distance between a Zr ion and its second nearest atoms occurred in aged 8YSZ. Aging caused a noticeable decrease in the relaxation peak of internal friction in 8YSZ. These phenomena are attributed to the short range ordering of oxygen ion vacancies around a Zr ion that results from relaxation in the anisotropy of periodical lattice distortion. Therefore, it is concluded that the trapping of oxygen ion vacancies at Zr ions in order to relax such distortion is responsible for a decrease in conductivity with aging. The relaxation peak of internal friction before aging changed with increasing dopant concentrations, and the behavior of this change from 8YSZ to 10YSZ was very similar to that when 8YSZ was aged, and that from 10YSZ to 15YSZ was similar to that when a single crystal of 10YSZ was aged. This marked similarity indicates that the changes in crystal structure which cause the decrease in conductivity with increasing dopant concentration are caused by the short range ordering of oxygen ion vacancies brought about by relaxation of the distortion, similar to those when conductivity decreases with aging.

RELAXATION PHENOMENA IN NITROGEN AUSTENITIC STEELS

In 1953 Finkelstein and Rozin published an article about a relaxation peak of internal friction (IF) in carbon containing CrNi 25 20 austenitic steel at 300 C at a frequency of {approximately} 1 Hz. They attributed damping to migration of carbon atoms in FCC lattice but did not specify if any possible mechanism of relaxation would be involved. Later on Ke and Tsien observed this peak in manganese and chromium-nickel-manganese austenitic steels. The mechanism suggested included the reorientation, under external stress, of atomic pairs formed by carbon atoms with substitutional atoms or vacancies, which created tetragonal distortions in FCC and lattice and, thus, caused a Snoek-like mechanism of relaxation. A number of versions of noncubic defects in fcc lattice responsible for Snoek-like relaxation were discussed. The aim of this study is to identify the possible relaxation mechanism taking place in the nitrogen austenite in connection with the nature of impurity atoms.

Impurity‐Enhanced Intergranular Cavity Formation in Silicon Nitride at High Temperatures

The effect of trace impurities on high‐temperature strength is examined in Si3N4 sintered without additives. Strength degradation above 1000°C occurs only in the low‐purity material, which also exhibits an intergranular slow crack growth (SCG) rate 2 orders of magnitude faster than that of the high‐purity material at 1400°C. A relaxation peak of internal friction is observed only in the low‐purity material, at ≅1200°C, and the origin of this peak is ascribed to the initial stage of SCG—that is, the cavity‐nucleation stage, enhanced by impurities. Based on the present results, a model for impurity‐enhanced SCG is proposed.

On the internal friction peak in boron fibres

The temperature spectrum of the internal friction (IF) at twisting and bending vibrations of boron fibres in the temperature range of 300–1100 K is studied. A broad IF relaxation peak is found. A model is suggested, based on the interphase diffusion interaction in the region of the fibre core, which allows an assessment to be made of the content of borides in the core and an evaluation of the kinetic parameters determining the formation of these phases.