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Aluminum-matrix-nanoparticle composites were produced by ball milling of micro scale aluminum powder with different additions of 500 nm mean diameter SiC particles in air atmosphere with subsequent consolidation by hot extrusion. The material was investigated in this condition by tensile testing, hot tensile testing, density, hardness, and amplitude dependent damping measurements. The amplitude dependent damping of the material was investigated after slow furnace heating and cooling as after quenching into water to the room temperature. The results of the tensile and hot tensile testing show that the addition of SiC particles lead to a significant increase of tensile strength, but the remaining porosity increased, too. The results obtained for the amplitude dependent damping can be attributed to cracks present in the consolidated material or cracks produced by thermal stresses. [ABSTRACT FROM AUTHOR]

Abstract: Ageing commercial WE43 magnesium alloys at 643K for various times up to 10,000s promotes the development of P1 precipitates, which strengthen the matrix. However, overageing causes P2 precipitates, which soften the matrix, to develop. Room temperature plastic deformation of samples aged at 643K causes (a) the generation of new dislocations and (b) the dissolution of the previously developed strengthening P1 precipitates. These effects are revealed by (a) the decreased micro yield stress, (b) the increased part of the measured internal friction which is independent of the amplitude, and (c) the decreased integrated intensity of the diffraction peak related to P1. [Copyright &y& Elsevier]

Abstract: Surface defects were produced onto commercial grain oriented iron silicon steel coated with forsterite by laser scribing and by chemical etching. Laser intensity was varied from 1 to 10kW/cm2 and also the defect raster was varied. Dynamic hysteresis loops of unscribed and scribed electrical steel sheets have been measured in the range of 0.05–500Hz using Epstein frames and a computer-controlled hysteresis recorder. From dynamic hysteresis loops the dynamic and static power losses were separated. In addition to the well-known reduction of dynamical losses also a reduction of the static hysteresis losses up to 5% due to the surface treatment was found when low laser intensities were used. It is assumed that this is due to a higher mobility of new 180° domain walls created by the surface treatment. The higher number of mobile Bloch walls in the electrical steel sheets lead to the reduction of static losses, too. [Copyright &y& Elsevier]

Mechanical spectroscopy and electrical resistivity measurements were performed on QE22 alloy. A new damping peak at around 530K, at a frequency of about 1Hz, promoted by the precipitation of semicoherent and incoherent precipitates was discovered. The activation energy of the precipitation process was also obtained. [Copyright &y& Elsevier]

Mechanical spectroscopy, electrical resistivity and X-ray diffraction measurements were performed on commercial WE 43 magnesium alloy with different thermal histories in order to determine the precipitation processes which appears within the temperature range between room temperature and 823 K.It has been found out that the precipitation process at temperatures of about 650 K promotes two stages of precipitations. The first occurring at earlier times produces an increase of the modulus and the later one leading to softening by growing of precipitates and a decrease of solid solute concentration in the matrix.The damping spectrum in WE 43 magnesium alloy shows three grain boundary damping peaks. The characteristic grain boundary peak of magnesium at 450 K, a grain boundary peak related to the solute atoms at 490 K and a grain boundary peak related to precipitates at grain boundaries at 520 K. [Copyright &y& Elsevier]

Copper oxide, silicon carbide and alumina–zirconia nanopowders have been produced by laser ablation in different atmospheres. Particle morphology, phase transformation and powder composition were investigated by X-ray diffraction, transmission electron microscopy, high resolution electron microscopy, and infrared spectroscopy. Targets used for producing the corresponding nanopowders usually melt, evaporate, decompose and oxidize during laser ablation, which lead to phase transformations and composition changes. A model has been proposed to explain the formation mechanism of nanoparticles, especially the nanoparticles embedded in amorphous matrices. [Copyright &y& Elsevier]

Light metals have high thermoelastic internal friction due to high coefficients of thermal expansion which has to be considered for various structural damping investigations. The thermoelastic effect of a powder metallurgically produced aluminium composite DISPAL™ and a magnesium casting alloy AZ91 (9 wt.% Al, 1 wt.% Zn) was investigated by measurements of the logarithmic decrement of free vibrations of bending beams. Because of inhomogenous stress distribution, a temperature gradient occurs between the compressed and the extended surface of the specimen, which leads to a transverse heat flow. This causes damping that is sensitive to the frequency of vibration. When the time of stress reversal equals the time necessary for heat flow from the compressed to the extended regions, a maximum of the logarithmic decrement occurs. The damping was measured as a function of the specimen thickness and the frequency of vibration ranging from 10 to 130 Hz. The frequency range was realised by both, a variation of the thickness and the mass at the end of the bending beams. By drawing the logarithmic decrement versus the product of the frequency and the quadratic thickness, a Debye peak is obtained which overlays all other damping mechanisms. The thermal diffusivity was calculated by determining the position of the maximum of the peak. The height of the peak, Young''s modulus and the specific heat of each sample were used to calculate the coefficient of thermal expansion of the specimens. The values agree, within the limits of scatter, with values measured by a dilatometer and taken from the literature, respectively. [Copyright &y& Elsevier]

Damping measurements have been carried out on the widely used commercial magnesium alloy AZ91 both unreinforced and reinforced with δ-alumina short fibres by the melt infiltration technique. The damping was determined after isochronal heat treatments by the measurement of the logarithmic decrement of free bending beam vibrations at frequencies ranging from 65 to 85 Hz. The thermoelastic and external apparatus damping were subtracted to obtain the damping, which can be mostly attributed to the dislocation movement. A maximum hardness and internal friction as a function of the annealing temperature at about 260°C both for unreinforced and reinforced AZ91 was found. This could be correlated with the precipitation of Mg17Al12 (β-phase). In comparison with the unreinforced AZ91 for the composite a general increase in damping was observed. All measurements of the logarithmic decrement up to an annealing temperature of about 413°C were explained by a model of Granato and Lu¨cke. For higher temperatures a strong increase in damping could be observed and was correlated with the formation of cracks. [Copyright &y& Elsevier]

Texture and magnetic properties of double-roller meltspun FeSi6.5% ribbons were investigated. Thin ribbons show a strong {1 0 0}〈0 v w〉 texture in the as-quenched state which develops to a {1 0 0}〈1 3 0〉 texture after annealing at 1200°C. The magnetic losses and the coercivity decrease by a factor of 2–3 due to annealing; they are somewhat higher compared to single-roller ribbons. [Copyright &y& Elsevier]

Abstract: The influence of high cycling on the damping behaviour of QE22 magnesium alloy reinforced by short Saffil fibres was investigated. The damping was measured as a logarithmic decrement of free vibration. Mechanical cycling was done in the apparatus for damping measurement at room temperature. Variation of the strain amplitude independent component of the damping was found with increasing the number of cycles. Changes in the dislocation substructure due to dislocation–dislocation and dislocation–interface interactions are responsible for this effect. [Copyright &y& Elsevier]

Abstract: Samples of 3Y-PSZ (with yttria partially stabilized zirconia) ceramics were produced in a form of rectangular bar by uniaxial pressing with subsequent sintering and grinding. In some samples crack-type defects were induced under the larger surfaces by green-body pressing with very high pressure. The strain amplitude-dependent damping of these samples was measured in a single cantilever arrangement as the logarithmic decrement of free decaying bending vibrations. An increase of damping with strain amplitude was found. Compared to the samples without induced defects the samples with induced defects showed higher damping for all strain amplitudes and their damping increases strongly with increasing strain amplitude. Moreover, in the samples with induced defects, the damping for bending vibrations perpendicular to the defect-affected surfaces is much lower than parallel to those. Damping of the samples could be increased by bending fatigue performed in the apparatus by which the damping was measured. After a heat treatment up to 300°C a decrease of damping was found which could possibly indicate healing of cracks. The results demonstrate that the measurement of internal friction is a powerful tool for detection of typical flaws such as pressing or sintering defects or cracks and can be used for non-destructive testing of ceramics. [Copyright &y& Elsevier]

Abstract: Mechanical spectroscopy has been used in order to investigate thermal stresses relaxation in the QE22 magnesium alloy (Mg–2Ag–2Nd) reinforced with 20vol.% of δ-alumina short fibers (Saffil® fibers). Composite has been processed by a squeeze cast technique. Specimens have undergone thermal cycling between 20 and 450°C with different temperature rate and excitation frequency ω. The relaxation of thermal stresses gives rise to additional internal friction. The mechanical loss versus temperature spectrum showed a transient maximum while heating and two maxima while cooling. A model where thermal stresses are relaxed by dislocation motion controlled by a solid friction mechanism has been used to interpret the experimental results. [Copyright &y& Elsevier]

Abstract: The influence of cyclic bending on the damping behaviour of AZ91 magnesium alloy-based composite was determined at room temperature. The logarithmic decrement of free decaying vibrations of bending beams as a function of the number of cycles exhibits four regions. In the first region, damping increases due to an increase of the dislocation density. Then steady state, a constant logarithmic decrement follows. The third region is characterised by a rapid decrease of the logarithmic decrement. Cracks nucleation in the matrix was manifested by a rapid increase of damping with increasing number of cycles and finally by failure of the sample – the fourth region. [Copyright &y& Elsevier]

When a metal matrix composite is subjected to temperature changes, thermal stresses arise at the interfaces between the matrix and the reinforcement as a result of the considerable mismatch between the thermal expansion coefficients of the matrix and the reinforcement. Even moderate temperature changes can produce thermal stresses that exceed the matrix yield stress. Consequently, new dislocations are generated at the interfaces causing thermal fatigue (microstructural changes, matrix plastic deformation and irreversible shape changes). The microstructural changes in the matrix can be detected by damping and stress relaxation measurements. The logarithmic decrement and modulus defect were measured after thermal treatment at temperatures between room temperature and temperatures up to 400°C. The strain dependence of the logarithmic decrement can be divided into two regions. The values of the logarithmic decrement are also influenced by heat treatment and foreign atoms in the matrix. The results can be explained assuming that straining and thermomechanical treatment produce changes in the microstructure of the composites. The stress relaxation curves were analysed and the modulus defect, relaxation strength and activation energy for dislocation motion were estimated. It is very difficult to draw conclusions on the mechanisms responsible for the stress relaxation but part of the relaxation strength is due to reversible dislocation movement. [Copyright &y& Elsevier]

An electro-rheological model based in Voigt units which takes into consideration the variation in volume promoted by electrostriction is developed. The model was based on a mean field approximation as an averaging of the mechanical and electrical properties. The electro-rheological coupling which describes the effects of the electrical excitation on the mechanical response and the effects of the mechanical excitation on the electrical response of the dielectric is studied. In the case of an alternating electrical excitation the model reveals the appearance of harmonics in the current through the dielectric promoted by the electrostriction phenomenon. In contrast, for the case of an oscillating mechanical excitation, a current which overtakes the driving mechanical oscillation was resolved to appear. The correlation of the new model with experimental results, obtained from dynamic mechanical analysis tests conducted under high electric field, in polyamide, was found out. [ABSTRACT FROM PUBLISHER]

Abstract: The change of magnetic properties of soft magnetic composites filled with iron cobalt particles from 10 to 80vol% filler fraction due to an alignment of particles by an external uniaxial magnetic field was measured. Relative changes of permeability values due to an alignment show an increase with a maximum at 30vol% filler fraction and losses are reduced for frequencies f >50Hz. Inner demagnetizing fields are reduced evoked by a more micro-homogeneous structure of the composite sample material. [Copyright &y& Elsevier]

Abstract: The CrV-alloyed heat-treatable steel (51CrV4) used for shafts is studied with respect to the influence of different heat treatment and deformation regimes on amplitude (strain amplitude 10−6–10−3) and temperature dependent (293–800K; 1–600Hz) damping. Specimens with different metallographic constituents were measured with and without magnetic field to distinguish between dislocation and magnetoelastic damping. Coercivity of all samples as well as microhardness increases in the order: ferrite–pearlite, as received, bainite and martensite. A clear difference in temperature and amplitude dependent internal friction was detected, too. A Snoek-Köster peak was found to be highest in martensitic state correlating with the dislocation density and reversible relaxation strength. Reversible stress relaxation measurements performed at room temperature from 3s to 1h and at a strain of 2×10−5 led to a reversible relaxation strength of 0.001 for all mentioned metallographic constituents except the martensitic one which was observed to be about four times higher. [Copyright &y& Elsevier]

Abstract: Coercivity, hardness and amplitude dependence of damping of electrochemically deposited nickel layers were measured directly after electrochemical deposition and subsequently after isochronal heat treatments at various annealing temperatures. All as-electrodeposited nickel samples have ultrafine grains with mean grain sizes in the order of 300nm. The co-deposition of nanoscaled ceramic SiO2-particles led to a reduction of the grain size to 60nm. The amplitude dependence of damping with and without saturating DC magnetic field, coercivity and microhardness was measured at room temperature after electrodeposition and after successive step by step isochronal heat treatments for increasing annealing temperatures. The heat treatments with increasing temperature led to progressive grain growth in the originally ultra fined grain material. By measuring the amplitude dependence of damping with and without magnetic field magneto-elastic and dislocation damping could be separated. It is shown that the increase in the grain size leads to smaller coercivity and therefore to higher damping, as expected. The amplitude dependent magneto-elastically caused damping was determined as the difference between the damping measurements without and with magnetic field for the same specimen. For annealing temperatures higher than 200°C an inverse proportionality between the slope of logarithmic decrement versus strain amplitude and the square of coercivity was observed like expected from theory. [Copyright &y& Elsevier]

Abstract: Ultrafine-grained Mg (UFG-Mg) samples were prepared by milling of powder in an inert atmosphere and subsequent compacted and hot extruded. The linear grain size of the specimens estimated by X-ray line profile analysis was about 100–150nm. Compression tests were performed at temperatures between room temperature and 300°C. The yield stress as well as the maximum stress decreases with temperature. This decrease and the steady-state character of the stress–strain curves at elevated temperatures indicate possible contributions of recovery processes. The influence of cyclic bending on the damping behaviour of UFG-Mg was determined at room temperature. The logarithmic decrement of free decaying vibrations of bending beams was determined as a function of the cycle number. Changes in the microstructure are manifested by changes in damping as well as in the resonant frequency. Cracks nucleation and growth in the material was manifested by a rapid increase of damping with increasing number of cycles and finally by failure of the sample. [Copyright &y& Elsevier]

Damping in cellular metallic materials is enhanced by localised stresses in comparison with the corresponding dense materials. A pronounced increase in damping with the amplitude of vibration interferes with an additional time dependence due to fatigue processes. This effect, attributed to growth and movement of cracks, is observed in Al- and Zn-based foams, porous steel and titanium. A model of this contribution to amplitude dependent damping is discussed using a simulation of experimental data for a porous 316L (FeNiCr) steel. [Copyright &y& Elsevier]

The strain dependencies of the logarithmic decrement and stress relaxation have been measured for magnesium alloy ZE41 (4%Zn–1%RE–balance Mg) reinforced by short Saffil fibres. Prior to the measurements, the samples were subjected to thermal cycling with increasing upper temperatures. The response of the composite on thermal loading has been characterised by measurements of acoustic emission (AE) and dilatation during thermal cycling. The AE activity during sample cooling was found to intensify with increasing upper temperature of the cycle, which indicates that the internal thermal stresses exceed the matrix yield stress in certain temperature intervals. The thermal stresses may relax by collective dislocation generation and motion. Thus, the threshold values of the upper cycle temperature for matrix yielding and thereby pronounced AE activity have been found. The combination of in situ dilatation and in situ AE measurements helped to clarify the contribution of various deformation mechanisms to the dimensional changes during thermal cycling of ZE41 composite. [Copyright &y& Elsevier]

A decrease of the temperature dependent coercive forces up to around 370 K is discovered in iron silicon alloys, both in quenched samples and in samples which were previously thermally treated to achieve the highest magnetic quality. Alloys of composition Fe-6 wt.% Si and Fe-3 wt.% Si are studied. This reduction in the coercive force is controlled by an increase in the mobility of the domain walls due to the increase in the dislocation's mobility enhanced by the movement of vacancies. It is worthwhile to mention that this reduction in coercive force is only present at these slightly elevated temperatures which are markedly smaller than the usual annealing temperatures for heat treatment of iron silicon alloys while it disappears again at room temperature. Neutron thermodiffraction, magnetic hysteresis loops tracer and mechanical spectroscopy are used as experimental techniques. • Iron silicon alloys, Fe-6.0 wt% Si and Fe-3.1 wt% Si. • Decrease in the value of the coercive force in around 40% which develops up to 370 K. • Mobility of the domain walls controlled by the dislocation's mobility. • Dislocation's mobility enhanced by the movement of vacancies. [ABSTRACT FROM AUTHOR]

We describe the influence of the density of dotted lines produced by laser scribing on the domain structure and shape of the hysteresis loops, which are different for samples with high density of dotted lines in comparison to that of samples with optimum density of dotted lines (leading to largest decrease of loss) was observed. [Copyright &y& Elsevier]