Papers by Keyword: Internal Friction

Abstract: To verify the assumption that the anelastic relaxation effect observed in Ni₃Al is due to stress-induced reorientation of antisite Al atoms [Numakura and Nishi, Mater. Sci. Eng. A 442 (2006) 59-62], the magnitudes of the anisotropic distortion produced by the intrinsic point defects have been evaluated by ab initio calculations. The anisotropy of the λ tensor (the strain per unit concentration of a particular defect) for the two candidate defect species, namely a Ni vacancy and an antisite Al atom, has been computed by full structure optimization of a supercell containing a single point defect: the difference in the principal values is +0.46 and −1.12, respectively. The relaxation strength estimated for antisite Al atoms agrees fairly well with experiment, while that for Ni vacancies is far too small because of their much lower concentration. The relaxation is, therefore, conclusively attributed to antisite Al atoms.

Abstract: Considering that, in Accordance with the Laws of Physics, the Sound Travels only through Elastic Bodies, the Main Characteristic of an Acoustic Material is the Elasticity. Classifying the Metallic Materials in this Regard is Quite Difficult, as the Elasticity is Characterized by more than One Component (static Elastic Modulus, Dynamic Elastic Modulus, Static Elastic Limit, Elastic Limit, Elastic Deformation Linearity, Damping Capacity). Best Acoustic Properties of some Metallic Materials are Widely Used in the Construction of Transducers, Musical Instruments, Bells Etc. for this Purpose, a Study on Three Metallic Materials was Conducted: a Cusn Alloy for Bells, a Cast Aluminum Alloy and a Martensitic Cast Iron. this Study Highlights both the Chemical Composition, Structure, Mechanical Properties and Damping Capacity of Sounds.

Abstract: We presented the comparative influence of two different grain size on bake hardenability for low carbon steel dependent internal friction (IF) spectra. Samples that had a ferrite structure consisting of two peaks and a linear background. Analyzed the grain size and grain boundary length of low carbon steel by EBSD technique. The results showed that: the grain refinement increased the number of initial solute carbon atoms and the effect of movable dislocations pinning by carbon. So grain refinement of low carbon steel could enhance its bake hardening properties.

Abstract: The bulk nanocrystalline aluminum are fabricated by cryomilling and hot-press sintering. The internal friction (IF) and relative dynamic modulus measurements in the nanocrystalline aluminum (Al) have been made using a multifunction internal friction apparatus (MFIFA) at low frequencies (0.2-3.0 Hz) over the wide temperature ranges from room temperature to 450 °C, while continuously changing-temperature forced vibration measurement. In the temperature spectrums of IF during heating process and cooling process, a distinct IF peak is found. Corresponding to the IF peak, the relative dynamic modulus decreases rapidly. The peak temperature of the IF peak shifts towards higher temperature with increasing frequency, i.e., the IF peak seem due to the thermal activated relaxation process. The IF peak is a grain boundary IF peak, which is associated with the diffusive grain boundary of Al/Al. Its activation energy has been calculated to be 2.21±0.04×10^-19 J and the pre-exponential factor is 10^-14 s in IF measurements.

Abstract: Resonant ultrasound spectroscopy (RUS) was applied to monitor the micro-cracking process occurring during cooling at polished surfaces of an ultrafine-grained AZ31 magnesium alloy. It was observed that although the net of micro-cracks covered only narrow regions along the edges of the sample, its appearance resulted in a strong increase of the attenuation of the free elastic vibrations, and was, thus, sensitively detectable from the evolution of the RUS resonant spectra with temperature. This approach enabled a reliable determination of the threshold temperature for micro-cracking.

Abstract: Heavily deformed 18-carat yellow gold samples show a recrystallization peak at 700 K during the first heating. The mechanical loss spectrum of polycrystals shows a relaxation peak at about 780 K, which is absent in single crystals made from the same alloy. Stepwise deformation of a single crystal from 2 % to 10 % causes an increase of the high temperature mechanical loss background and the appearance of a high temperature peak. At 8 % deformation the high temperature peak disappears and the peak that is normally observed in polycrystals appears. The increase of the exponential background is interpreted as due to the introduction of new dislocations whereas the high temperature peak is attributed to a relaxation mechanism in the sub grain boundaries. The peak of polycrystalline samples located at intermediate temperatures depends on the grain size: with grain growth, the peak position shifts to higher temperatures. The peak temperature can be related to the mean grain size.

Abstract: This work describes the anelastic behaviour of human dentin in the temperature range from 100 K to 673 K. Human molars, extracted from individuals (males 55-70 years old) as part of their dental treatment, were cut to obtain bar-shaped samples for mechanical spectroscopy (MS) experiments. The results are presented and discussed in two parts referring to experiments above and below room temperature.

Abstract: The temperature and amplitude dependence of internal friction fcc Mn45Cu55 alloy aged at 400 °C were studied. Two low-temperature internal friction peak observed in the quenched state. Physical mechanism of the peaks was determined by the effect of frequency and strain amplitude on the temperature dependence of internal friction. The influence of the heat treatment to the internal friction of the investigated alloy was shown.

Abstract: This paper reports on the tension-compression asymmetry of [001]-oriented Co49Ni21Ga30 single crystals at elevated temperatures. Maximum strains of -4.8 % and 8.6 % in compression and tension, respectively, were found. A linear Clausius-Clapeyron relationship was observed for both stress-states where the smaller slope in tension resulted in a significant increase of the phase transformation temperatures with stress, which reached 180 °C under a constant stress level of 150 MPa. In addition, the material demonstrated a large pseudoelastic temperature range of about 300 °C under both stress state conditions. The results in this study unequivocally indicate the potential of these alloys for applications where elevated temperatures and stress levels prevail.