Internal Friction Experiments Research Articles

A combined thermal desorption spectroscopy and internal friction study on the interaction of hydrogen with microstructural defects and the influence of carbon distribution

Hydrogen interactions with different microstructural defects were analysed in ultra-low carbon steel, with specific focus on the influence of carbon distribution. For this purpose, the steel was cold rolled and subjected to various annealing treatments, obtaining microstructures ranging from as cold rolled, over recovered up to fully recrystallized. Optical microscopy, transmission electron microscopy and hardness measurements were used to obtain information on the grain boundary structure and dislocation density. Positron annihilation spectroscopy measurements revealed metastable open volume defects related to both dislocations and vacancy clusters. The carbon distribution was characterized by internal friction experiments. Hydrogen interactions were studied by thermal desorption spectroscopy and internal friction measurements of samples electrochemically pre-charged with hydrogen.The most dominant contribution in hydrogen trapping in the cold rolled material is provided by dislocations. However, their contribution is strongly reduced after annealing at temperatures in the range between 300 K and 600 K due to dissolution of metastable kink-pairs and small carbon-vacancy clusters. Dissolution of such clusters provides fresh supply of carbon to dislocations, which reduces the dislocation trapping capacity for hydrogen due to carbon-hydrogen repulsion. The presence of carbon also reduces the vacancy mobility, allowing clustering and growth during cold rolling resulting in strong hydrogen trapping sites. Binding energies at dislocations were obtained from thermal desorption spectroscopy and internal friction measurements and compared to various models. The small discrepancy in the activation energy is argued to originate from the quantum effect. Hydrogen release from vacancy clusters is determined by the energy required for complete cluster dissolution.

Split-vacancy defect complexes of oxygen in hcp and fcc cobalt

One of the most ubiquitous and important defects in solids is oxygen. Knowledge about the solubility and diffusivity of oxygen in materials is crucial to understand a number of important technological processes, such as oxidation, corrosion, and heterogeneous catalysis. Density-functional theory calculations of the thermodynamics and kinetics of oxygen in cobalt show that oxygen diffusing into the two close-packed phases, namely $\ensuremath{\alpha}$ (hcp) and $\ensuremath{\beta}$ (fcc), strongly interacts with vacancies. We observe the formation of oxygen split-vacancy centers (V-${\mathrm{O}}_{\mathrm{i}}$-V) in both phases, and we show that this defect complex exhibits a similar migration energy barrier to the vacancy and oxygen interstitials. In contrast to the vacancy and oxygen interstitials, the oxygen split-vacancy centers exhibit an anisotropic strain field that couples to applied stress, making it possible to observe them through an internal friction experiment on quenched cobalt.

Atomistic modelling of the diffusion of C in Fe[sbnd]Cr alloys

The diffusion of C in FeCr solid solutions is modelled and compared to experimental data. A set of binding energies and migration barriers for C diffusion in different local chemical environments are first calculated using density functional theory. A pair interaction model is developed in order to reproduce these data and predict the migration barriers in other environments. The diffusion model is then implemented in a kinetic Monte Carlo method to simulate tracer diffusion experiments, using a standard procedure, and internal friction experiments, using a novel method. Simulations of internal friction show a unique Snoek peak in the whole concentration range, between pure iron and pure chromium. The average migration barrier for C diffusion in FeCr alloys is found to increase progressively with the Cr concentration, with a small rate below 6 %Cr. In Cr-rich alloys, the effective migration barrier for C diffusion is found to be larger in tracer diffusion than in the internal friction simulations. We conclude that the effective migration barrier extracted from tracer diffusion is closely related to trapping effects of C atoms in Fe-rich local environments, whereas the migration barrier associated with internal friction is mainly controlled by the migration barriers of the most probable configurations, as it is clearly shown in the Cr-rich domain.

The investigation of strength and plasticity mechanism of low-temperature annealed ultrafine grained stainless steel

The properties of steel material can be greatly improved when its grain size becomes finer, so grain refinement is the most commonly used to improve the strength, ductility and impact on the toughness of steel at the same time. Compared to ordinary fine-grained steel, the average grain size of ultra-fine grained steel is less than 2 μm and it has different strength and plasticity mechanism. In this paper, effect of low-temperature annealing on the microstructure and properties of ultra-fine grained stainless steel in internal friction was studied by utilizing transmission electron microscope (TEM) and universal tensile testing machine. At the same time, the strength and plasticity mechanism of ultra-fine grained stainless steel was revealed by internal friction experiments. The results show that with the increase of annealing time and annealing temperature, both the tensile strength and yield strength decreases, while the elongation increases continuously. The mechanical properties of tested steel are more sensitive to the temperature. In the internal friction curve of tested steel, the peak of P1 which result from the interaction between solid solution atoms and dislocations increases first and then decreases, while the peak of P2 which result from the interaction between dislocation and carbide precipitates decreases first and then increases. The peak of P3 which result from the structure, area and movement of grain boundary decreases continuously. The strength and plasticity mechanism of tested steel at room temperature is the result of interaction between the grain boundary and dislocation.

An Overview of Research into Low Internal Friction Optical Coatings by the Gravitational Wave Detection Community

The direct detection of gravitational waves by ground-based interferometric gravitational wave detectors in recent years has opened a new window of the universe, allowing the astrophysical observations of previously unexplored phenomena, such as the collisions of black holes and neutron stars. However, small thermodynamic fluctuations of the density of the thin films that compose the mirrors used within the gravitational wave detectors, such as the LIGO and Virgo detectors, give rise to noise which limits these instruments at their most sensitive frequencies. This "Brownian Thermal Noise" can be related to the inherent internal friction of the mirror materials through the fluctuation-dissipation theorem. Therefore, the improved sensitivity of gravitational wave detectors depends, to some extent, upon the development of optical thin films with low internal friction. The past two decades have therefore seen the growth of internal friction experiments undertaken within the gravitational wave detection community. This article attempts to summarize the results of these investigations and to highlight current research directions in order to foster a stronger dialogue with the larger internal friction and mechanical spectroscopy community.

Twinning in Ni–Fe–Ga–Co shape memory alloy: Temperature scaling beyond the Seeger model

The temperature dependence of the macroscopic de-twining stress in Ni–Fe–Ga–Co shape memory alloy is proportional to the temperature dependence of the micro-yield stress. This proportionality holds for all values of the reversible anelastic strain derived from non-linear internal friction experiments and contradicts predictions of the Seeger model for the temperature dependence of the yield stress. The Seeger model requires two length scales which leads to the independence of two yield stress components. Instead, we find the self-affine behaviour of anelastic strain, which excludes all separations of lengthscales.

Structure of nanoscale copper precipitates in neutron-irradiated Fe-Cu-C alloys

The structure of copper nanoclusters/precipitates formed under neutron irradiation in Fe-0.3 wt. % Cu-C alloy is studied by the internal friction and positron annihilation experiments of postirradiation annealed alloys. The appearance of a carbon-relaxation peak during the first recovery stage at about 723 K reveals the fact that complex carbon-vacancy-copper clusters have formed during the irradiation-mediated copper precipitation process. The stability of Cu-C-vacancy clusters is confirmed by ab initio calculations. The existence of a structural phase transition of copper precipitates is observed in the alloys that are annealed at temperatures between the first and second recovery stages, which indicates that the dissociation of vacancies and carbon atoms from the vacancy-copper-carbon clusters is accompanied by the crystallization of Cu precipitates.

Toughness and Internal Friction of Weld Metal Welded by High-Current MAG Welding

Low-temperature impact test on four different kinds of weld metal welded by different technologies of high-current MAG welding was carried out in this paper. The results show that different materials and different welding parameters have different effect on impact energy. As the chemical analysis and observation from the optical microscope show that When welding material contains appropriate C, Si, Ti, fine acicular ferrite forms in it; on the contrary, crisp and thick bainite appears. Compares to acicular ferrite which has an Akv>27J at -27°C and better toughness, bainite has a poor toughness and an Akv<27J. The internal friction experiments show that there are two internal friction peaks - Snoek and SKK. The peak is clear when the microstructure is bainite, on the other side, the microstructure is acicular ferrite.

Effects of Rare Earth on the Impact Toughness of High-Carbon Steel

The effects and mechanism of cerium, lanthanum and cerium-lanthanum alloys on microstructure and the impact toughness of high-carbon steel were studied in the present work. For high-carbon steel, the state and the content of RE were measured, and the effects and the mechanism of RE on sulfide inclusions, microstructure and the impact toughness of steel were determined. With increasing the RE addition, the sulfide inclusion can be changed from strip-like, spindle, ellipsoidal and spheric in shape. Strip-like sulfide disappears in high-carbon steel with the RE addition being 0.05%. A small quantity of RE can fine the austenitic grain, decrease the height of the SKK peak of the internal friction curve, and improve the impact toughness of high-carbon steel evidently. And the effects of lanthanum on fining the austenitic grain and improving the impact toughness is the largest, next to that of cerium-lanthanum alloys, and that of cerium is the least, which can be verified by the internal friction experiments.

Mechanical Spectroscopy Study on Cu<sub>53.5</sub>Zr<sub>42</sub>Al<sub>4.5</sub> Alloy

This study consists of the characterization of the anelastic properties of a Bulk Metallic Glasses (BMG) by mechanical spectroscopy, which can be defined as an energy absorption technique. The equipment used was the acoustic elastometer system, the anelastic relaxation spectra were carried out with a heating rate of 1 K/min and vacuum better than 10-5 torr, in the temperature range of 300 K to 640 K. The amorphous sample studied, with nominal composition of Cu53.5Zr42Al4.5, was processed by skull push-pull casting technique in a rectangular cavity cooper mould. Differential scanning calorimeter (DSC) curves have evidenced the amorphous structure although the X-ray diffraction (XDR) pattern has indicated a heterogeneous microstructure with amorphous matrix and some metaestable nanocrystalline phases which have not been identified yet. The dynamical elastic modulus of this alloy (between 54 GPa and 58 GPa at room temperature) and internal friction patterns as temperature function implied an increase of the crystalline phase during the measurements. This effect was confirmed with new X-ray diffraction measurements after the internal friction experiments.

On the Stacking Fault Energy of Fe-18 Pct Mn-0.6 Pct C-1.5 Pct Al Twinning-Induced Plasticity Steel

The stacking fault energy (SFE) of Fe-18 pct Mn-0.6 pct C-1.5 pct Al twinning-induced plasticity (TWIP) steel was measured using weak-beam dark-field imaging of dissociated dislocations observed in transmission electron microscopy. The SFE was found to be 30 mJ/m2. A relatively wide scatter was observed in the experimentally measured partial dislocation separation of screw dislocations. It is argued that the anomalously wide partial dislocation separation is due to the interaction of point-defect pairs involving interstitial C atoms with the strain field of the partial dislocations. Internal friction (IF) experiments were carried out to detect the presence of point-defect pairs that might affect the dislocation separation, and a clear Finkelshtein–Rosin (FR) peak related to point-defect pairs involving interstitial C atoms was observed in the IF spectrum.

Carbon impurity dissolution and migration in bcc Fe-Cr: First-principles calculations

First-principles density-functional theory calculations for C solution enthalpies, H-sol, and diffusion activation enthalpies, H-diff, in body-centered-cubic Fe and Cr are presented. The results for C in Fe compare well with experiments, provided that the effect of magnetic disordering is accounted for. Likewise, in Cr, the calculated Hsol and Hdiff agree well with available experiments. In both materials, the deviation between calculated enthalpies and critically assessed experimental enthalpies are less than 0.05 eV. Further, first-principles calculations for the interaction energies between a solute (e.g., a Cr atom in bcc Fe) and an interstitial C atom are presented. The results are in conflict with those inferred from internal friction (IF) experiments in disordered Fe-Cr-C alloys. A simple model of C relaxation in disordered Fe-Cr is used to compare theoretical and experimental IF curves directly. The results suggest that a more extensive study of the energetic, thermodynamic, and kinetic aspects of C migration in Fe-Cr is needed.

Experimental and theoretical study of annealed Ni-Pt alloys

In this communication we present a detailed study of the magnetic properties of ordered Ni-Pt alloys. We study the alloys through field-cooled and zero-field cooled dc magnetization, nonlinear ac susceptibility and sound velocity and internal friction experiments. We also present a theoretical analysis of the magnetic moments in these alloy systems. Our analysis, both experimental and theoretical, will show that disorder has a large impact on the magnetism in the samples in the composition range of 40--60% Ni. We shall argue that any disorder still remaining in the annealed samples will crucially alter the magnetic moment in this composition range and is the most probable reason for the discrepancies between earlier experimental investigations.

Measurement of sensitivity to dynamic strain aging in C–Mn steels by internal friction experiments

The dynamic strain aging (DSA) phenomenon is present in C–Mn steels and associated welds commonly used in many industrial applications. This phenomenon, which appears in metals containing solute atoms interacting with dislocations, induces an increase in flow stress and ultimate tensile strength (UTS) as well as a decrease in ductility. The DSA phenomenon was studied by tensile, strain rate sensitivity and internal friction tests between 20°C and 350°C in two C–Mn steels with very different sensitivities to DSA (a fully killed A42 steel and a semikilled A48 steel). The internal friction technique, which allows one to evaluate the balance between carbon and nitrogen atoms free in the lattice and carbon and nitrogen atoms interacting with mobile dislocations, appears to give results well correlated with those obtained by tensile (and strain rate sensitivity) tests. The ductility loss or the UTS increase is shown to be proportional to Snoek peak height. It is concluded that, even in industrial materials, a single internal friction test can give a good evaluation of DSA sensitivity.

Internal friction evidence of uncorrelated magnetic clusters in electron-doped manganite Sr 0.8Ce 0.2MnO 3

Electron-doped manganite Sr 0.8Ce 0.2MnO 3 has been systematically investigated by X-ray diffraction, electronic transport, magnetic, internal friction, and Young's modulus experiments. The X-ray diffraction result indicates that the compound remains tetragonal (I4/mcm) structure at room temperature. Due to the strong Jahn–Teller (JT) distortion, the ground state is antiferromagnetic (AFM) insulator. Below 20 K, a spin-glass (SG) state dominates at low temperatures. In the paramagnetic (PM) region, an internal friction peak at around 250 K, which is characteristic of relaxation, has been observed. Under applied magnetic field, the internal friction peak moves to higher temperature, which is suggested to originate from the formation of ferromagnetic (FM) clusters in PM region. In addition, the softening of Young's modulus in the vicinity of AFM transition temperature is interpreted in terms of the strong electron–phonon interaction.

Low-temperature internal friction and thermal conductivity in plastically deformed metals due to dislocation dipoles and random stresses

The contribution to the low frequency internal friction and the thermal conductivity due to optically vibrating edge dislocation dipoles is calculated within the modified Granato-Lucke string model. The results are compared with the recent experiments on plastically deformed samples of Al, Ta and Nb at low temperatures. It is shown that the presence of a reasonable density of optically vibrating dislocation dipoles provides a good fit to the thermal conductivity in superconducting samples. At the same time, the internal friction experiments can not be described within the standard fluttering string mechanism. We found that the problem can be solved by assuming random forces acting on the dislocation dipoles. This gives an additional contribution to the internal friction which describes well the experimental data at low temperatures while their contribution to the thermal conductivity is found to be negligible.

Grain-Boundary Wetting-Dewetting in z= 1 SiAlON Ceramic

The grain-boundary structure of a model SiAlON polycrystal with nominal composition Si5AlON7 was characterized by transmission electron microscopy (TEM) both in an equilibrium (as-processed) state at room temperature and after quenching from elevated temperature. In addition, low-frequency (1–13 Hz) internal friction data were recorded as a function of temperature, showing a pronounced grain-boundary sliding peak positioned at 1030°C. High-resolution transmission electron microscopy (HRTEM) of the equilibrated low-temperature microstructure revealed residual glass only at multigrain junctions, but no amorphous intergranular films were observed. The detection of clean interfaces in the as-processed sample contradicts the internal friction data, which instead suggests the presence of a low-viscosity grain boundary phase, sliding at elevated temperatures. Therefore, a thin section of the as-sintered material was heated to 1380°C and rapidly quenched. HRTEM analysis of this sample showed, apart from residual glass pockets, wetted grain boundaries, which is in line with the internal friction experiment. This wetting-dewetting phenomenon observed in z= 1 SiAlON is expected to have a strong impact not only on high-temperature engineering ceramics but also on geological, temperature-activated processes such as volcanic eruptions.

Grain-Boundary Viscosity of Preoxidized and Nitrogen-Annealed Silicon Carbides

Internal friction experiments were conducted on a model SiC polycrystal prepared from preoxidized (high-purity) SiC powder. This material contained high-purity SiO2 glass at grain boundaries in addition to a free-carbon phase, which was completely removed upon powder preoxidation. Comparative tests were conducted on a SiC polycrystal, obtained from the as-received SiC powder with the addition of 2.5 vol% of high-purity SiO2. This latter SiC material was also investigated after annealing at 1900°C for 3 h in a nitrogen atmosphere. Electron microscopy observations revealed a glass-wetted interface structure in SiC polycrystals prepared from both as-received and preoxidized powders. However, the former material also showed a large fraction of interfaces coated by turbostratic graphite. Upon high-temperature annealing in nitrogen, partial glass dewetting occurred, and voids were systematically observed at multigrain junctions. The actual presence of nitrogen could only be detected in a limited number of wetted interfaces. A common feature in the internal friction behavior of the preoxidized, SiO2-added and nitrogen-annealed SiC was a relaxation peak that resulted from grain-boundary sliding. Frequency-shift analysis revealed markedly different characteristics for this peak: both the magnitude of the intergranular glass viscosity and the activation energy for grain-boundary viscous flow were much higher in the nitrogen-annealed material. Results of torsional creep tests were consistent with these findings, with nitrogen-annealed SiC being the most creep resistant among the tested materials.

Oxygen mobility in yttria-doped zirconia studied by internal friction, electrical conductivity and tracer diffusion experiments

Ionic conduction and oxygen diffusion in Y 2O 3-doped zirconia are due to the mobility of oxygen vacancies. Vacancy association reactions with Y cations can be classified using the activation enthalpies ΔH determined by various methods in dependence of the yttria content (3–24 mol%). ΔH O for oxygen tracer diffusion is independent of the yttria content (average value ΔH O=0.95 eV). The activation enthalpy of electrical conductivity, ΔH DC, rises from 1.05 to 1.5 eV, with increasing Y 2O 3 content, pointing to growing association effects. In dielectric loss experiments, slightly higher activation enthalpies were found. In internal friction experiments, localized jumps of vacancies bound to yttrium ions can be observed as Debye loss peaks. Here, the activation enthalpy ΔH ML rises with increasing Y 2O 3 content from 0.9 to 1.6 eV. The results are discussed with respect to the combined effect of migration, association and interaction of oxygen vacancies and stabilizer cations.

Defects and phase transitions in yttria- and scandia-doped zirconia

Internal friction (IF) experiments were performed on the systems ZrO 2 (8–12 mol%)–Y 2O 3, and ZrO 2 (9–12 mol%)–Sc 2O 3. The following features were found: (i) an IF peak around 500 K in both systems which is assigned to the hopping of trapped oxygen vacancies (Δ H=1.2–1.3 eV); (ii) in polycrystalline materials a high temperature damping background, which is related to cation diffusion; (iii) an order/disorder phase transition at 1450 K in ZrO 2–12 mol%Y 2O 3; and (iv) in ZrO 2–Sc 2O 3 a ferroelastic׃↔ferroelectric phase transition at 750 K from the rhombohedral to the cubic phase. Cation diffusion experiments in ZrO 2–Sc 2O 3 revealed an activation enthalpy for Zr diffusion of 5.3 eV indicating that short- and long-range cation transport is governed by one type of cation diffusion process.