Internal Friction Measurements Research Articles

(Digital Presentation) Anelasticity, Mechanical Spectroscopy, Internal Friction in Radiation and Structural Functionalized Nanocomposites of Multiwalled Carbon Nanotubes and Polyamide, Polyvinylchloride, Polyethylene, SiO2

Experimental Methods Ultrasound (US) impulse-phase method using computerized “KERN-4” with frequencies f┴ ≈ 0,7 MHz and f║ ≈ 1 MHz was used [1,2]. The measured velocity error was equal to ΔV/V ≈ 1,5%. Results and Discussion The influencing of ultrasonic deformation εUS was researched on mechanical properties of nanocomposite. The important value is in position of formation in the polymeric matrix of molecular structures, as multiwalled carbon nanotubes serve as the centers of crystalline phase nanocomposite origin. Amplitude-dependent internal friction (ADIF) measurement can be used as the highly sensitive method of monitoring the nanoplastic deformation eND of nanocomposites. ADIF measurement makes it possible to record the moment of dislocation segments LC separation from stoppers. Internal friction (IF) is caused by various relaxation processes that are related to nanocomposites structure defectiveness. Even rather small strain can collect up in non-ideal nanocomposites, changing their anelastic and elastic characteristics. One of the ways to purposefully change the properties of multiwalled carbon nanotubes in order to use them in nanoelectronics is to introduce impurities of other elements. It was found that as the result of the structural defect annealing IF background Q0 -1 significantly decreases during measuring of IF temperature dependences Q-1(T), which indicates the improvement of nanocomposite structure. The samples were prepared by ultrasonic dispersion using digital ultrasonic (US) bath CE-6200A with power W = 70 W at frequency f ≈ 42 kHz [1,2]. Illustration of the window for processing data of quasilongitudinal elastic waves velocity measuring V║ = 3244 ± 10 m/sec m/sec in nanocomposite polyamide (PA-6) (NH(CH2)5CO)n + 0,1% multiwalled carbon nanotubes (MCNT) by by pulse-phase US method at frequency f║ ≈ 1 MHz after electron irradiation with dose De- ≈ 10 MRad with energy Ee- ≈ 2,0 MeV is represented in Fig. 1. Fig.1. Illustration of the window for processing data of quasilongitudinal elastic waves velocity measuring V║ = 3244 m/sec in nanocomposite polyamide (PA-6) (NH(CH2)5CO)n + 0,1% MCNT by pulse-phase US method at frequency f║ ≈ 1 MHz after electron irradiation with dose De- ≈ 10 MRad.Poisson coefficient μ and elastic modulus E completely characterize the elastic properties of polymer nanocomposite. Poisson coefficient μ - elastic value of ratio of relative transversal compression e^ to relative longitudinal lengthening e║ [1]. One oscillator produces 3 waves: 1 longitudinal and 2 transversal. Debye temperature θD was determined after the formula [2], where kB - Boltzmann constant, h - Plank constant, NA - Avogadro number, A - middle gram-molecular mass, V║ - quasilongitudinal US velocity, V┴ - quasitransversal US velocity.Complex elastic modulus of nanocomposite polyamide-6 (PA-6) (NH(CH2)5CO)n + % MCNT E* is equal to the sum of elastic dynamic modulus E’ = rV║ 2 and loss modulus E” = E’d [2], where δ - logarithmic decrement of US attenuation, ρ - nanocomposite density, V║ - longitudinal US elastic waves velocity, Q-1 - internal friction, where α - US attenuation coefficient, λ - US wavelength, f - US frequency. Internal friction is equal Q-1 = δ/π. The logarithmic decrement of attenuation δ of US oscillations with amplitude A = A0e- d x is equal: δ = ln(An+1/An). Conclusions The presence of the strong interaction for nanocomposite between polyamide-6 (NH(CH2)5CO)n and multiwalled carbon nanotubes was confirmed.The increase of the nanocomposite crystallinity degree at growth of multiwalled carbon nanotubes concentration filling with the nanotubes of matrix results in the decline of content of organized phase.The phenomenon of change of Poisson coefficient m, Debye temperature θD, dynamic elastic modulus E’ = rV║ 2, dynamic shear modulus G = rV^ 2 under the influence of radiative electronic e- radiation is caused by the appearance of primary radiation defects (RD). As the result of interdefect interactions primary RD form secondary RD. Acknowledgments This work has been supported by the Ministry of Education and Science of Ukraine: Grant of the Ministry of Education and Science of Ukraine for the prospective development of the scientific direction “Mathematical sciences and natural sciences” at Taras Shevchenko National University of Kyiv. References Onanko, A.P., Kuryliuk, V.V., Onanko, Y.A. et al. Features of inelastic and elastic characteristics of Si and SiO2/Si structures. Journal of Nano- and Electronic Physics13(5), 05017(5) (2021).Onanko, A.P., Kuryliuk, V.V., Onanko, Y.A. et al. Mechanical spectroscopy and internal friction in SiO2/Si. Journal of Nano- and Electronic Physics14(6), 06029(7) (2022). Figure 1

Effects of Proline on Internal Friction in Simulated Folding Dynamics of Several Alanine-Based α-Helical Peptides.

We have studied in silico the effect of proline, a model cosolvent, on local and global friction coefficients in (un)folding of several typical alanine-based α-helical peptides. Local friction is related to dwell times of a single, ensemble-averaged hydrogen bond (HB) within each peptide. Global friction is related to energy dissipated in a series of configurational changes of each peptide experienced by increasing the number of HBs during folding. Both of these approaches are important in relation to future atomic force microscopic-based measurements of internal friction via force-clamp single-molecule force spectroscopy. Molecular dynamics (MD) simulations for six peptides, namely, ALA5, ALA8, ALA15, ALA21, (AAQAA)3, and H2N-GN(AAQAA)2G-COONH2, have been conducted at 2 and 5 M proline solutions in water. Using previously obtained MD data for these peptides in pure water as well as upgraded theoretical models, we obtained variations of local and global internal friction coefficients as a function of solution viscosity. The results showed the substantial role of proline in stabilizing the folded state and slowing the overall folding dynamics. Consequently, larger friction coefficients were obtained at larger viscosities. The local and global internal friction, i.e., respective, friction coefficients approximated to zero viscosity, was also obtained. The evolution of friction coefficients with viscosity was weakly dependent on the number of concurrent folding pathways but was rather dominated by a stabilizing effect of proline on the folded states. Obtained values of local and global internal friction showed qualitatively similar results and a clear dependency on the structure of the studied peptide.

Monitoring and quantification of ultrasonic fatigue damage in copper based on internal friction measurement

Fatigue damage in metals and alloys would reduce their strength and should be identified as early as possible. However, fatigue damage is usually difficult to detect even using advanced nondestructive testing method. Here we developed an automated damping monitoring system for ultrasonic fatigue testing based on a quantitative electromechanical impedance method. During fatigue testing, the damping and resonance frequency of the Piezo actuator/horn/specimen system is measured regularly using an impedance analyzer. When the system damping suddenly increases, it implies that fatigue damage may be generated in the specimen. Separate impedance measurements on the copper specimen in a vacuum chamber show that the internal frictions of damaged specimens are much larger than the fresh specimens. Subsequent X-Ray micro-CT scanning shows that microcracks up to 0.8 mm in length were generated in those fatigued specimens with increased internal frictions. Further tensile testing shows that compared to the fresh specimen, specimens with fatigue damage exhibits reduced tensile strength and elongation at break. Furthermore, the larger the internal friction, the smaller the remaining yield strength and a nearly linear relationship between them holds. Finally, a damage variable DQ is defined based on internal friction which can act as a measure of fatigue damage in metals.

Effects of aluminum and oxygen additions on quenched-in compositional fluctuations, dynamic atomic shuffling, and their resultant diffusionless isothermal [formula omitted] transformation in ternary Ti–V-based alloys with bcc structure

Diffusionless isothermal ω transformation is a recently discovered ω transformation that occurs isothermally during aging near room temperature in Ti alloys with a bcc (β-phase) structure. Unlike conventional displacive phase transitions, the diffusionless isothermal ω transformation occurs in locally unstable nanoscale β-phase regions formed by quenched-in statistical compositional fluctuations. In the present study, the effects of Al and oxygen additions in ternary β-phase Ti–V-based alloys on the diffusionless isothermal ω transformation and its attempt process, called dynamic atomic shuffling, were studied. Elastic constant and internal friction measurements for Ti–16.6V–2.1Al and Ti–17.5V–2.5O (at.%) alloy single crystals and analysis of quenched-in compositional fluctuations using the thermodynamic theory of fluctuations indicated that the oxygen addition increases the β-phase stability, and it selectively increases the activation energy of dynamic atomic shuffling in locally unstable Ti-rich regions, which is caused by the strong attractive interaction between Ti and oxygen elements. As a result, oxygen addition suppresses the diffusionless isothermal ω transformation that occurs during aging at 298 K. In contrast, low β-phase stability, which promotes ω-phase nucleation, is retained by Al addition. Furthermore, dynamic atomic shuffling with a low activation energy is retained even though the average activation energy is enhanced by the Al addition, originating from the relatively weak atomic interaction between Ti and Al. Therefore, the diffusionless isothermal ω transformation cannot be suppressed by Al addition.

Systematic error in the internal friction measurement of coatings for gravitational wave detectors

Low internal friction coatings are key components of advanced technologies such as optical atomic clocks and high-finesse optical cavity and often lie at the forefront of the most advanced experiments in Physics. Notably, increasing the sensitivity of gravitational-wave detectors depends in a very large part on developing new coatings, which entails developing more suitable methods and models to investigate their loss angle. In fact, the most sensitive region of the detection band in such detectors is limited by the coating thermal noise, which is related to the loss angle of the coating. Until now, models which describe only ideal physical properties have been adopted, wondering about the use of one or more loss angles to describe the mechanical properties of coatings. Here we show the presence of a systematic error ascribed to inhomogeneity of the sample at its edges in measuring the coating loss angle. We present a model for disk-shaped resonators, largely used in loss angle measurements, and we compare the theory with measurements showing how this systematic error impacts on the accuracy with which the loss model parameters are known.

Recrystallization in Ti5553 and Ti4733 detected by mechanical spectroscopy

This paper proposes a new way to detect recrystallization in beta-metastable alloys Ti5553 and Ti4733. Samples of these alloys were cold rolled and thermally treated. Internal friction was measured during heat cycles using a torsion pendulum. A correlation between recrystallization and sharp peak in internal friction specra was shown. The mechanism of dissolution of alpha phase triggering the recrystallization is proposed. In subsequent temperature cycles, the internal friction high temperature background decreases and stabilizes after three cycles. This is attributed with secondary recrystallization leading to grain growth. The size of the grains for different recrystallization time and temperature was measured and is coherent with the mechanical spectroscopy results. This result tends to prove that internal friction measurement can be used to optimize recrystallization treatment in beta metastable titanium alloys.

Ultra-high mechanical damping during superelastic bending of micro pillars and micro beams in Cu-Al-Ni shape memory alloys

Mechanical spectroscopy techniques and internal friction measurements have historically offered a key contribution to the understanding of fundamental mechanisms of defects mobility and phase transformations in many kinds of materials. Nowadays, at the beginning of the millennium, the apparition of the new paradigm of nanotechnology reveals new unforeseen properties of the materials at the nano-scale. Nevertheless, instrumented nanoindentation appears as a new mechanical spectroscopy technique to approach the measure of internal friction at the nano-scale through the direct evaluation of the loss factor η. Indeed, nano compression tests on micro and nano pillars recently measured ultra-high mechanical damping in several Cu-based shape memory alloys (SMA). A step forward is given in the present work, approaching the design of potential micro dampers of SMA working in bending and torsion modes. Several micro devices were milled by focused ion beam (FIB) technique, on [001] oriented single crystals of a Cu-Al-Ni SMA. Ultra-high mechanical damping is demonstrated during superelastic bending of square section micro pillars by in-situ testing inside the scanning electron microscope, using a flat apex 60º-conical indenter in off-axis mode. Then, a series of micro beams and micro cantilevers were designed and milled by FIB, and tested using instrumented nanoindentation equipment by applying the load in bending mode as well as in a mixed bending-torsion mode during off-axis tests. In all cases, the internal friction, or mechanical damping per cycle and per unit of volume, was calculated from the measured load-displacement curve. Superelastic cycling during bending of micro pillars, micro beams and micro cantilevers, exhibits stable and reproducible ultra-high mechanical damping with a loss factor η > 0.1. These results paved the road for designing micro-dampers of Cu-based SMA, able to work in different mechanical modes of compression, bending and torsion, opening the way for many applications of mechanical damping at the nano-scale.

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.

Atomistic investigation on the impact of substitutional Al and Si atoms on the carbon kinetics in ferrite

The pairwise interactions of substitutional solute atom X = Al, Si with interstitial carbon at stable (octahedral) and saddle-point (tetrahedral) positions in body-centered-cubic iron (α-Fe) are computed using density-functional theory. These pairwise interactions are used in atomistic kinetic Monte Carlo approach to simulate carbon internal friction and tracer diffusion measurements in Fe-Si, Fe-Al, and Fe-Al-Si ferritic alloys without any adjusting parameters. The good agreement between the simulated and experimental Snoek relaxation profiles validates the pair interaction model for kinetic simulations. The predicted effect of Al on slowing down carbon diffusion is consistent with previous studies. We highlight a super-cell size effect on the Si-carbon interactions obtained from first principles. Using a carefully tested database, it is shown that the introduction of Si into ferrite only decreases the carbon diffusivity below a critical temperature.

Comparison of internal friction measurements on Ni-Ti reinforced smart composites prepared by additive manufacturing

Polymer 3D printing has been utilised in aerospace to produce complex lightweight structures, in medical fields to print tissues and organs, and in a number of other industries to combat the rising demand for weight-saving engineering solutions. Pure polymer goods created through 3D printing, on the other hand, lack strength and functionality. Therefore, by combining matrix and reinforcing materials, 3D printing of polymer composites can overcome these problems. Also various researchers have used matrix system either epoxy resin or vinyl ester resin. Despite its wide usage, resins have few drawbacks like microleakage and high curing time which could be eliminated by 3D printing. In this work, we have focused on using 3D printed polymer matrix system. To enhance the property, shape memory alloys (SMAs) are introduced in the structure as a reinforcement. Shape memory alloys are a class of smart material that, when heated over a certain temperature, can recover deformation. SMAs exhibit two main characteristics i.e., shape memory effect (SME) and superelasticity (SE). SMAs are available in a variety of shapes, including wires, springs, sheets, and tubes. The SMA wires can be embedded in the composites for a variety of reasons, such as enhancing mechanical properties, shape morphing of structures and for use as actuators. Damping is one such mechanical property which can enhanced by reinforcing SMA wires. In this research work, the samples were fabricated using 3D printing of PLA and PETG with SMA wires embedded in two different forms i.e., continuous and discontinuous. The samples were then examined under a dynamic mechanical analyzer to study the damping (internal friction) behaviour of the smart composites. It has been found that the incorporation of SMA wires into the matrix had a significant influence on the dynamic mechanical properties. Also, the samples with SMA reinforced in continuous manner had the higher value of tan δ i.e., it had good damping properties in comparison to short fibre reinforced composites.

Modeling the Snoek peak in bct-martensite

Snoek relaxation in bcc crystals is the delayed strain response to an applied stress resulting from the interaction of the interstitial atoms with the stress field. It is responsible for the Snoek peak observed in internal friction measurements of ferrite. However, although martensite is carbon supersaturated, several authors denied the possibility of Snoek relaxation in bct-martensite. We investigated this matter by means of Monte Carlo simulations and mean-field thermo-kinetic modeling. Our results show that Snoek relaxation does occur in bct-martensite. The computed Snoek profiles of temperature-dependent and frequency-dependent internal friction exhibit unexpected features: both peak height and peak temperature decrease when the carbon content is increased. We explain this behavior in the frame of the linear-response approximation. Our theoretical predictions are in qualitative agreement with experiments.

Amplitude-dependent internal friction of dislocation interactions in dual-phase steel

Abstract Dislocation interactions in the ferrite matrix of a dual-phase steel have been studied as a function of martensite volume fraction (11 – 25%) and tensile straining (0 –5 %) by strain-induced amplitude-dependent (strain amplitude varying from 10– 7 to 10 –4) internal friction measurements at room temperature, using a high-frequency composite oscillator (40 kHz). Results showed that a higher volume fraction of martensite increases the internal stress in the softer ferrite matrix and restricted the dislocation motions, giving rise to a lower amplitude-dependent internal friction. Application of tensile straining further shortened the effective mobile dislocation length which was revealed by the internal friction measurements and this resulted in a high initial strain hardening rate of the high-martensite samples. Reduction in the martensite volume fraction and the mobile dislocations in the ferrite matrix through process control resulted in an increase in the amplitude-dependent internal friction, indicating a longer effective mobile length of dislocations which, in turn, delayed early necking of the dual-phase samples during tensile straining.

Thermal stability of SPD-processed aluminum alloys - Internal friction as an indication for recovery, recrystallization and abnormal grain growth

In this study, we investigate the effect of different microstructures generated by severe plastic deformation on the thermal stability of an age-hardenable Al–Mg–Si alloy (AA6082). To analyze recovery and recrystallization we investigate the internal friction at various excitation frequencies and the microstructural evolution of the material in a wide range of temperatures. Severely deformed conditions of the alloy show a distinct increase of internal friction and a pronounced reduction of the materials hardness at elevated temperatures. Microstructural investigations reveal that different stages of recovery and recrystallization take place during the heating process. In a certain case, a remarkable correlation between frequency-dependent internal friction and abnormal grain growth in the microstructure is found. It is derived that internal friction measurements help to characterize the thermal stability of SPD processed materials. Since thermally-induced microstructural changes are directly related to changes of internal friction, these measurements help to identify characteristic temperatures of recovery, recrystallization and abnormal grain growth.

Study of anisotropy through microscopy, internal friction and electrical resistivity measurements of Ti-6Al-4V samples fabricated by selective laser melting

PurposeThis paper aims to investigate the microstructural anisotropy of Ti-6Al-4V samples fabricated by selective laser melting.Design/methodology/approachSpecimens are fabricated through a Renishaw AM400 selective laser melting machine. Three microstructures (as-built, 850°C annealed and 1,050°C annealed) and two building orientations, parallel (PA) and perpendicular (PE) to the building platform, are considered. Starting from in-depth microscopic observations and comprehensive electron backscattered diffraction imaging, the study addresses non-conventional techniques such as internal friction and electrical resistivity measurements to assess the anisotropy of the fabricated parts.FindingsMicroscope observations highlight a fine texture with columnar grains parallel to the building direction in the as-built and 850°C annealed samples. Besides, coarse grains characterized the 1,050°C annealed specimens. Internal friction measurements pointed out the presence of internal stress while storage modulus analyses appear sensitive to texture. Electrical resistivity is resulted to be dependent on grain orientation.Originality/valueThe work uses some novel characterization techniques to study the anisotropy and internal stresses of Ti-6Al-4V samples processed by selective laser melting. Mechanical spectroscopy results suitable in this kind of study, as it mimics the operating conditions of the material.

Elastic constants and internal friction of forged β-solidifying TiAl alloys at room temperature and high temperature

Forged β-solidifying TiAl alloys can exhibit nine independent elastic constants in accordance with the orthorhombic symmetry of forging texture. In this study, we measured the elastic constants and high-frequency internal friction of two forged Ti–43Al–5V–4Nb (in at.%) alloys with nearly lamellar and triplex microstructures using resonant ultrasound spectroscopy at temperatures between room temperature and 760 °C. We demonstrated that a two-step heat treatment after the forging process produces nearly isotropic elasticity in the TiAl alloys, and the elastic anisotropy is virtually constant with temperature. The Young's modulus of the TiAl alloy with a triplex microstructure was comparable to that of the alloy with a nearly lamellar microstructure. In addition, the triplex-microstructure TiAl alloy showed a significant energy loss for shear vibration modes compared with the nearly lamellar alloy. These findings are supported by the effect of the hexagonal ω-phase present in the βo-phase on mechanical stiffness and loss. Internal friction measurements at high frequencies exhibited an internal-friction peak at approximately 200 °C, which may be related to the isothermal ω-phase. This research may contribute to the development of sophisticated forged TiAl components.

Detecting fatigue in aluminum alloys based on internal friction measurement using an electromechanical impedance method

Detecting mechanical fatigue of metallic components is always a challenge in industries. In this work, we proposed to monitor the low-cycle fatigue of a 6061 aluminum alloy based on internal friction (IF) measurement, which is realized by a quantitative electromechanical impedance (Q-EMI) method using a small piezoelectric wafer bonded on the specimen. Large stress amplitude (230 MPa) was employed in the testing; thus, the fatigue life can always be below 105 cycles. It was found that except for the initial testing stage, the IF always increases steadily with the increasing fatigue cycles. Before the fatigue failure, the IF can reach 2.5–3.4 times the initial value, which is thought to be caused by the micro-cracks forming and growing. In comparison, the resonance frequency of the specimen just drops by about 2% compared with the initial value. Finally, a fatigue criterion based on IF measurement is suggested for aluminum alloys and it can also be extended to other metals.

Interaction of Mobile Dislocation with Additives in Ionic Crystals

The mechanical properties of materials are affected by the interaction of mobile dislocation with additive ions. Although this has been widely investigated by various methods (yield and proof stress measurements, microscopy observations of dislocation, internal friction measurements, stress relaxation tests and so on), it is difficult to obtain the information on mobile dislocation-additives interaction during plastic deformation of bulk.

Determination of recrystallization temperature of deformed high-purity Al assessed by internal friction technique

In this study, the recrystallization process in deformed high-purity aluminum was investigated by using the internal friction (IF) and hardness measurement. In the heating process, two IF peaks were detected when the heating rate is 2 °C/min: a sharp peak (P1 peak) at ~139 °C and a wide peak (P2 peak) at ~278 °C (0.5 Hz). In the subsequent cooling process, the P1 peak disappears while the P2 peak remains. The P2 peak shifted towards higher temperatures with increasing frequency and can be ascribed to grain boundary relaxation. For the P1 peak, however, its position did not change with increasing frequency but shifted towards higher temperatures with increasing heating rate in the range of 1–5 °C/min, and the corresponding modulus varied abnormally in the temperature range of 115–160 °C. These facts indicated that the P1 peak is a non-relaxational peak and can be ascribed to the recrystallization process. The recrystallization activation energy deduced via the shift of peak position with heating rate by using the Kissinger equation is 57± 3 kJ/mol, which is as same as that deduced from the classical isothermal recrystallization process as assessed by microhardness measurement. The classical isothermal recrystallization temperature can be deduced from the peak temperature of P1 peak by simply adjusting the heating rate. This provided a method to determine the recrystallization temperature via internal friction measurement in a continuously heating process, which needs only two or three samples.

Theoretical investigation of the 70.5[formula omitted] mixed dislocations in body-centered cubic transition metals

The low-temperature plasticity of body-centered cubic (bcc) metals is governed by 12〈111〉 screw dislocations due to their compact, non-planar core. It has been proposed that 70.5° mixed (M111) dislocations may also exhibit special core structures and comparably large Peierls stresses, but the theoretical and experimental evidence is still incomplete. In this work, we present a detailed comparative study of the M111 dislocation in five bcc transition metals on the basis of atomistic simulations. We employ density functional theory and semi-empirical interatomic potentials to investigate both the core structure and the Peierls barrier of the M111 dislocation. Our calculations demonstrate that reliable prediction of M111 properties presents not only a very stringent test for the reliability of interatomic potentials but is also challenging for first-principles calculations for which careful convergence studies are required. Our study reveals that the Peierls barrier and stress vary significantly for different bcc transition metals. Sizable barriers are found for W and Mo while for Nb, Ta and Fe the barrier is comparably small. Our predictions are consistent with internal friction measurements and provide new insights into the plasticity of bcc metals.

Effects of Fe Addition on the Phase Transformation Internal Friction in Ni-Al-Based Alloys

The influences of chemical compositions on the internal friction of phase transformation were investigated for the quenched Ni-Al-based alloys. The internal friction measurements were completed using a low-frequency mechanical spectrum apparatus through forced vibration method. It was shown that the chemical compositions have the great influences on the internal friction of phase transition for the oil-cooled Ni-Al-based alloys. The peak-temperature of internal friction is lowered, and the peak-height is increased and the peak-width is narrowed when Fe content is elevated. The reducing of the peak-temperature is attributed to the increase of stability of γ phase due to the addition of Fe. The changes of the parameters of the peak are also related to the Aleq(equivalent Al) contents.