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We performed high-frequency (0.4–1.7 MHz) measurements of the internal friction (IF) on 14 bulk metallic glasses (MGs). It is found that 12 of these MGs display relaxation IF peaks at temperatures ≈ 400–500 K, which are weakly affected by heat treatment within the amorphous state. The corresponding relaxation time is about 0.3 μ s. This fast relaxation is reported for the first time in the literature. The apparent activation enthalpy for 4 MGs is determined. It is shown that if measured at a low frequency of 1 Hz, these IF peaks would appear near room temperature or by 30–50 K below it. Thus, the IF peaks found in the present investigation are direct analogues of low-temperature/low-frequency β ′ - and/or γ -relaxations described in the literature. It is argued that the origin of these IF peaks is related to the relaxation of structural defects similar to dumbbell interstitials, which are frozen in solid glass from the liquid state upon melt quenching. These defects can be considered as elastic dipoles and their re-orientation in the applied stress provides anelastic deformation and corresponding IF peak. After correction for temperature dependence of the shear modulus, the true activation enthalpy (0.62–1.08 eV) and activation entropy (4 ≤Δ S ∕ k B ≤15) for defect re-orientation are determined. • High-frequency (0.4–1.7 MHz) internal friction (IF) measurements are performed. • IF peak located at 400–500 K is found in 12 metallic glasses. • The relaxation time corresponding to this peak is about 0.3 μ s. • Corresponding activation enthalpy and activation entropy are determined. • The origin of the IF peak is supposed to be due to defect re-orientation. [ABSTRACT FROM AUTHOR]

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. • Ultra-high mechanical damping at nano-scale by bending micro beams and micro cantilevers. • Ultra-high damping during superelastic bending of micro beams of shape memory alloys. • In-situ nano-testing inside the electron microscope to measure damping at the nano-scale. • Nanoindentation reveals to be a new technique of mechanical spectroscopy. • Internal friction measured by nanoindentation in micro devices of shape memory alloys. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Ni-Ti reinforced smart composites was fabricated through additive manufacturing with 2 different matrix materials (PLA and PETG). • DSC and XRD were performed for characterising the Ni-Ti wire. • DMA was performed on the smart composite and the effect of different orientation and length of the SMA with 2 different matrix material on the internal friction was analysed. • PLA smart composite had higher internal friction value compared to PETG smart composite. [ABSTRACT FROM AUTHOR]

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. • Mechanical spectroscopy was used to detect recrystallization in Ti5553 and Ti4733 • Ti4733 shows a lower recrystallization temperature than Ti5553due to α " metastable phase dissolving at lower temperature • The dissolution of α and α " is important to achieve recrystallization • Heat treatment at the recrystallization temperature of deformed samples results in grain refinement [ABSTRACT FROM AUTHOR]

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. • The existence of Snoek relaxation in bct-martensite is demonstrated theoretically. • The Snoek peak height decreases when the solute carbon content is increased. • The peak temperature is carbon-content dependent. [ABSTRACT FROM AUTHOR]

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 (P 1 peak) at ~139 °C and a wide peak (P 2 peak) at ~278 °C (0.5 Hz). In the subsequent cooling process, the P 1 peak disappears while the P 2 peak remains. The P 2 peak shifted towards higher temperatures with increasing frequency and can be ascribed to grain boundary relaxation. For the P 1 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 P 1 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 P 1 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. • The P 1 peak associated with the recrystallization process of Al was detected. • Recrystallization activation energy of Al during continuously heating was estimated. • Classical recrystallization process was simulated via continuously heating process. • Feasibility of determining recrystallization temperature by IF was investigated. [ABSTRACT FROM AUTHOR]

• Influence of Nb on Ti diffusion observed in TiAl intermetallics for aeronautic applications. • γ-TiAl based alloys exhibit a common atomic relaxation associated with Ti diffusion. • Atomic mechanism of Ti diffusion impeded by Nb in γ-TiAl based alloys. • Mechanical Spectroscopy allows measuring diffusion at high temperature. The development of intermetallic titanium aluminides has been driven by the aeronautic and aerospace industries because of the excellent mechanical properties and low density of γ-TiAl based alloys. Up to now, several generations of γ-TiAl based alloys were developed with increasing complexity of the alloy systems. Nb is one of the most important alloying elements in γ-TiAl alloys and although it is considered as a slow diffuser, its influence has not been fully quantified yet. In this work we demonstrate, through mechanical spectroscopy measurements conducted on several γ-TiAl based alloys with different Nb content, that Nb impedes the diffusion of Ti atoms in the α 2 -Ti 3 Al phase. Internal friction measurements show a relaxation peak P(α 2), which is associated with short distance diffusion of Ti atoms in the α 2 phase, involving stress-induced rotation of dipoles Al-V Ti -Al, whose activation energy is dependent on the Nb content. The increase of the activation energy is quantified as ΔE a (Ti)= 0.037 eV × at% Nb, being attributed to the next-neighbor interaction of Nb atoms with the local configuration of Ti-V Ti. This mechanism also produces a further broadening of the relaxation peak, which is attributed to the near-next-neighbor interactions for high Nb contents. Finally, an atomic model for the mechanism responsible for this relaxation is proposed allowing to explain the observed experimental behavior. [ABSTRACT FROM AUTHOR]

The martensitic transformation of Ni 49.5 Ti 35.5 Hf 15 high temperature shape memory alloy is characterized by internal friction measurements. The temperatures for the reversible B2 ↔ B19' transformation appear in the range 410–479 K on cooling and 447–526 K on heating. In addition, a strong anomalous pre-martensitic softening of the dynamic modulus is reported in the high-temperature phase, between 850 K and 550 K, evidencing the thermoelastic character of this family of alloys. Based on the analysis of the internal friction spectra, a theoretical and experimental methodology is proposed to measure the Clausius-Clapeyron coefficient through mechanical spectroscopy. This new non-destructive method could be extremely useful for the development of advanced prototypes of shape memory alloys. • Internal friction on a Ni–Ti-Hf High-Temperature Shape Memory Alloys. • Martensitic transformation on a Ni–Ti-Hf High-Temperature Shape Memory Alloys. • Anomalous pre-martensitic softening measured on a Ni–Ti-Hf Shape Memory Alloy. • Mechanical Spectroscopy allows measuring the Clausius-Clapeyron coefficient. [ABSTRACT FROM AUTHOR]

Motivated to create a germanium analog to nearly two-level-tunneling-system (TLS)-free amorphous silicon, six germanium films, all about 350 nm thick, were deposited by molecular beam epitaxy onto substrates held at temperatures between room temperature and 280∘C. The internal friction and speed of sound of the films was measured between 375 mK and 300 K. Although the intent was to study amorphous thin films, those grown at 200∘C and higher were shown to be at least partially crystalline. The tunneling strength C , a measure of the interaction between phonons and two-level tunneling systems, decreased monotonically with increasing substrate growth temperature, and for films grown on substrates at temperatures above room temperature, C was below the glassy range. The lowest value for an amorphous film, for the 160∘C-grown film, was C = 1.9 × 10 − 5 . • Two-level Tunneling Systems measured in amorphous germanium via internal friction. • Fewer two-level systems as substrate temperature increases during film deposition. • Crystallization confounds higher temperature preparations of amorphous germanium. • Conflicting interpretations of amorphous germanium two-level systems are resolved. [ABSTRACT FROM AUTHOR]