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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. (C) 2020 Elsevier B.V. All rights reserved.

Alloys of CuAlMn are known as cheap, high strength shape memory alloys with an excellent damping capacity within their austenitic-martensitic phase transformation, compared to alloy systems like NiTi, CuZnAl or MnCu. But CuAlMn alloys have disadvantage due to generation of voids by a high shrinkage which further increases the existing proneness to stress cracks during rapid cooling. Alloying grain refining elements improves the stress crack resistance and enables a wide range of rapid quenching parameters which are needed to control the temperature of martensitic phase transformation. Additionally, the elements itself influence the in- or decreasing of the phase transformation temperature and the SMA effects. Furthermore, some of these elements can reduce the internal friction indirectly by decomposing areas of metastable martensite into its stabilized forms, where no transformation occurs. This thermic stability can be calculated by the concentration of valence electrons in a unit cell. The proneness to ageing is controlled by multistep heat treatments. Annealing and rapid quenching into the area of martensitic phase transformation maximize the generation of point defects. A high amount of point defects contradicts the negative effect of pinning. It also preserves the material from extreme brittleness. The influences of these effects are shown at single cantilever bending beams by elastic strain amplitude (ε = 12E-4) depending measurements of internal friction at natural frequency along the ageing at room temperature (293 K) up to 2500 h. The samples are annealed at 1123 K for 15 min (CuAl14Mn2) and 1100K for 30min (CuAl11Mn5) afterwards rapid quenched to 370 K with no further thermic stabilisation. The base alloy of CuAl14.1Mn2.0Ni1.9Fe0.4 had an internal friction measured as logarithmic Decrement (δ) of 0.155 and 0.11 after 2500 h of ageing at RT. The phase transformation is located between 284 K and 352 K, measured by DSC. The alloy of CuAl11.1Mn5.5Zn2.9Ni2.1 had a logarithmic decrement of 0.31 and diminish continuously to 0.12 after 2500 h of ageing at RT. The phase transformation is located between 287 K and 318 K.

The behaviour of damping and dynamic shear modulus in polypropylene charged with either different volume fraction or size of magnetite (Fe3O4) particles, as a function of the applied magnetic field at 318, 353 and 403K; has been studied. An increase of the alternating magnetic field oscillating with 50Hz, leads to an increase of the damping. In addition, during the subsequently decreasing alternating magnetic field, the damping decreases, but a hysteretic behaviour appeared. The behaviour of the damping and the elastic modulus under the application of an alternating magnetic field was explained by the development of a magnetic fatigue damage occurring around the particle interface due to oscillation of magnetite particles. In contrast, during the increase of a direct magnetic field, the damping decreases and the elastic modulus increases. Measurements performed at 353 and 403K allowed observing the interaction process among the particles of magnetite in the polymer matrix. After the decrease in the direct magnetic field, from the maximum reached value, damping and modulus remain smaller and higher, respectively; giving rise to a memory effect. In addition, a mesoscopic description of magnetite filled polymer composite materials has been performed in the continuous media by considering the interaction between magnetic and mechanical forces. Theoretical predictions of here developed model were qualitatively applied with good success for explaining the memory effect in magnetite filled polypropylene under the application of a direct magnetic field.

Aluminium-Matrix-Nanoparticle-Composites were produced by ball milling of micro scale Aluminium powder with various nanoscales ceramic powders like Silicon Carbide, Alumina and Boron Nitride with subsequent consolidation by hot extruding. The composites were investigated by amplitude dependent damping tests, tensile tests at elevated temperatures, hardness measurements, imaging methods and electric conductivity tests. All tested samples were machined out of hot extruded rods. The Amplitude dependent damping of bending samples was determined by measuring the strain dependent logarithmic decrement of free decaying vibrations of bending beams at room temperature. These tests were done after successive step by step isochronal heat treatments. Some samples show substantial improvement of the mechanical properties due to dispersion hardening or grain refinement. It can be concluded that the results are mainly influenced by dislocation effects like Orowan-effect, work-hardening, grain-size-hardening, recrystallization, and creation of dislocations at ceramic particles due to thermal mismatch. Moreover some results can be attributed to fatigue during mechanical cycling namely crack nucleation, crack growth and fraction. The electric conductivity was measured indirectly by permeability tests with a digital hysteresis recording devise. The results show the low influence of nano-particle dispersion hardening to conductivity in comparison of work-hardening.

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.

Because electric cars are manufactured in high quantities, the influence of punching of nonoriented electrical steel with respect to tool wear becomes an important topic for the automotive industry. With regard to quality assurance, it is necessary to investigate the local degradation of the magnetic properties due to the plastic deformation caused by the cutting process. In this contribution, both the local changes of the microstructure of the material and the magnetic properties will be considered. Different methods for analyzing the manufactured electrical steel laminations were applied. Cutting edges generated under different states of tool wear were examined by means of optical microscopy and electron backscatter diffraction to visualize the influence of plastic deformations. The magnetic properties of punched electrical steel laminations as a function of increasing tool wear have been determined by hysteresis measurements of stacked ring cores. With respect to quality assurance purposes spatially resolved measurements have been carried out to determine local magnetic properties and find a suitable correlation to application-relevant quantities.

In order to reduce the eddy current losses in electrical machines, stator and rotor cores are made of stacked electrically isolated steel sheets. For volume production of rotor and stator laminations in the automotive industry, the non-oriented electrical steel sheets are cut in a high speed punching process. Not only the material properties of the electrical steel but also the entire manufacturing process affect the magnetic properties of the stator and rotor components. In this contribution, the influence of plastic deformation on the microstructure at the cutting edges and on the resulting magnetic properties with respect to the selected cutting procedure was investigated. As a result of progressing tool wear, the degree of plastic deformation caused by the shearing procedure during the punching process increases. Furthermore, cutting parameters such as clearance and cutting speed have an effect on the magnetic properties of the steel laminations. The influence of tool wear and cutting speed on the material properties was analyzed by means of light microscopy, hysteresis measurements, and electron backscatter diffraction.

The amplitude dependent damping of two bending beam samples of magnesium alloy AJ91 (9 wt.% Al, 1 wt.% Sr) was measured at room temperature in as cast condition, after quenching from high temperatures into water of room temperature and after various bending cycles to fatigue. Some measurements were performed successively with about 33 Hz and 100 Hz resonant frequency. The measurements show typical dislocation damping in as cast condition, after heat treatment at temperatures lower than 420°C, and cycle numbers lower then 50.000. For higher quenching temperatures the damping increases over the whole measured strain range with increasing quenching temperature and number of cycles to fatigue. After quenching from temperatures higher than 478°C the crack damping becomes dominant. The effects of damping seem to increase with increasing frequency. In one sample damping of individual cracks could be identified in the amplitude dependent damping curves by their characteristic course very similar to the ones postulated in an earlier publication by a simple rheological model [4]. The extending of crack length leads to a shift of the damping to lower strains.

Magnesium matrix composites show improved wear resistance, enhanced strength and creep resistance in comparison with their monolithic counterparts, on the other hand keep low density and good machinability. Internal friction measurements are a suitable tool to detect changes in the microstructure of thermally or mechanically loaded composites. Samples from pure magnesium reinforced with zirconia nanoparticles were thermally cycled between room temperature and increasing upper temperature of thermal cycle. After thermal cycling amplitude dependence of damping measured in terms of the decrement was measured. Very high values of the logarithmic decrement are described to the poor binding between the matrix and ceramic nanoparticles. The influence of number of cyclic bending to fatigue on the damping behaviour of the same nanocomposite was determined at room temperature. The measured decrease of the resonant frequency indicates a loss of stiffness during cycling. Crack deflection along an interface is followed by the separation of the particle/matrix interface.

The behavior of internal friction Q -1 and dynamic shear modulus has been studied in polypropylene charged with either different volume fraction or size of magnetite (Fe 3 O 4 ) particles, as a function of the applied magnetic field at 318 K. An increase of the alternating (AC) magnetic field oscillating with 50 Hz, leads to an increase of the internal friction. In addition, during the subsequently decreasing alternating magnetic field, the internal friction decreases, but a hysteretic behavior appeared. In fact, the internal friction of the decreasing part of magnetic field amplitude is found to be smaller than during the previously increasing amplitude part of the treatment with the alternating magnetic field. Subsequent magnetic treatment cycles, lead to successively decreasing internal friction. In contrast, during the increase of a direct (DC) magnetic field, the internal friction decreases and the elastic modulus increases. The behavior of the internal friction and the elastic modulus during the application of an oscillating magnetic field (AC) is discussed on the basis of the development of both, a new zone with different rheological characteristics than the matrix but of the same material (self-inclusion), and/or a deteriorated or damaged zone (chain’s cuts) of the polymer matrix in the neighborhood of the magnetite inclusion. These effects are promoted by the movement or small relative rotation of the magnetite particles related to the surrounding matrix controlled by the oscillating field. The behavior of the internal friction and elastic modulus during the application of a direct (DC) magnetic field is discussed on the basis of the increase of the internal stresses into the polymer matrix due to the promotion of the magnetomechanical stresses.

Aluminum-matrix-nanoparticle-composites were produced by ball milling of micro scale aluminum powder in air atmosphere with subsequent consolidation by hot extrusion and also additional hot swaging. They were investigated in this condition after step by step isochronal annealing with successive increasing annealing temperature and quenching into water to room temperature. The material was investigated by amplitude dependent damping, hardness and density measurements, all at room temperature. For all measured amplitude dependent internal friction (ADIF) curves the damping increases with increasing strain amplitude. After some annealing treatments a knee occurs in the medium strain amplitude region of these curves. Moreover between annealing temperatures from 360 degrees C to 480 degrees C the strain dependent damping becomes a maximum, i.e. a peak in the ADIF curves occurs. Other ADIF curves of quenched and fatigued material show characteristic peaks that can be attributed to individual single cracks. It is shown that all these effects are due to the formation, opening and compression of cracks present in the sample or created by thermally exerted stresses.

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.

The annealing behaviour of temperature-dependent mechanical spectra (vibrating-reed technique) was studied on electrodeposited ultrafine-grained nickel as well as on Ni nanocomposites with small (7 nm) SiO2or larger (25 nm) Al2O3nanoparticles. From the response of the different phenomena involved – Young’s modulus, high-temperature damping background, dislocation-and hydrogen-induced low-temperature loss peaks, and magnetomechanical effects – information is obtained on processes such as recovery, grain growth, hydrogen trapping, and dislocation generation by thermal stresses, which are influenced by both kinds of nanoparticles in different ways.

Mechanical spectroscopy, differential scanning calorimetry measurements and light microscopy studies were performed on homogenised and plastically deformed samples of commercial WE43 magnesium alloy. Plastic deformation was performed both at 300 K and 643 K, and at 1 % and 10% of uniform plastic deformation. Samples 1 % deformed at 300 K did not show recrystallisation, but recovery at about 633 K was detected. Samples 1 % deformed at 643 K recovered dynamically, during hot working. Samples 10% deformed at 300 K began to recrystallise at about 730 K, meanwhile samples 10% deformed at 643 K dynamically recrystallised during hot working.

Magnesium matrix composites show improved wear resistance, enhanced strength and creep resistance in comparison with their monolithic counterparts. On the other hand they keep low density and good machinability. Internal friction measurements are suitable tool to detect changes in the microstructure of thermally or mechanically loaded composites. Samples from pure magnesium reinforced with zirconia nanoparticles were thermally cycled between room temperature and increasing upper temperature of thermal cycle. After thermal cycling amplitude dependence of decrement was measured. Very high values of the logarithmic decrement were ascribed to the poor binding between the matrix and ceramic nanoparticles. The influence of cyclic bending on the damping behaviour of the same nanocomposite was determined at room temperature. Measured decrease of the resonant frequency indicates the stiffness loss as a function of cycling. Observed decrease of amplitude independent component of decrement at the end of the sample life time is due to increase of the dislocation density. These dislocations can be absorbed by the interface. Crack deflection along an interface is followed by the separation of the particle/matrix interface.

The grain size of electrodeposited ultrafine grained nickel can be reduced from ∼300nm down to ∼60–150nm by adding ceramic nanoparticles such as Al2O3 or SiO2. The first results are presented using temperature-dependent mechanical spectroscopy (vibrating reed technique at ∼200–800Hz) applied to pure Ni as well as to Ni nanocomposites with very small (7nm) SiO2 or larger (25nm) Al2O3 particles, respectively. The mechanical spectra reveal several different elastic and anelastic phenomena: a high temperature damping background, irreversible changes in Young’s modulus, magneto-mechanical effects, and two low temperature loss peaks attributed to dislocations and to absorbed hydrogen, respectively. These phenomena and their different annealing characteristics are discussed in terms of underlying physical mechanisms and related processes of recovery and grain growth. The Ni/Al2O3 nanocomposite differs from the two other materials by effective suppression of matrix grain growth as manifested in the stabilisation of high temperature damping and absence of magneto-mechanical effects, and by the properties of the matrix/ceramic interfaces – with the incorporation of hydrogen and generation of dislocations by thermal stresses – as detected by the low temperature loss peaks. On the other hand, the annealing-induced increase in Young’s modulus, being more sensitive to the early stages of recovery, seems to be smaller with SiO2 than with Al2O3 particles (in spite of a lower stability against grain growth), which is not yet fully understood.

The mobility of dislocations has been investigated in WE43 magnesium alloy during recovery and recrystallisation for samples deformed plastically, at different degrees of plastic deformation and temperatures. The dislocation density decreases within the temperature range 550K-650 K, in good agreement with the characteristic recovery temperature of this alloy, 630 K. New dislocations located at the grain boundaries start their movement from 650 K onwards. During recrystallisation, which has a characteristic temperature of around 700K. the density of dislocations decreases and the possibility of movement of the dislocations also decreases, due to the development of internal stresses during the growth of new strain-free grains.The excess of vacancies promoted by the plastic deformation in cold worked samples is consumed up to temperatures of 550 K. New thermal vacancies which assist the movement of grain boundaries and dislocations are created after annealing at temperature above 650 K. Hot worked samples which exhibit dynamic recovery or recrystallisation, depending on the degree of plastic deformation; have a structure with both a scarce dislocations mobility and also a small dislocations density. [doi:10.2320/matertrans.M2010374]

Compared to their matrix metals Magnesium Matrix Composites (MMCs) show higher stiffness, strength, improved tribological properties, lower thermal expansion coefficient, improved wear resistance, enhanced strength and creep resistance. Moreover they own low density and good machinability. Investigation of their physical and mechanical properties is important not only for applications but also for better understanding of the processes responsible for their behavior. Squeeze casting as an advanced technology of MMCs production became possible to combine metallic materials with ceramic reinforcing fibers and so to modify not only mechanical and thermal characteristics but also damping capacity. On the other hand damping capacity measurements are suitable tools to detect changes in the microstructure of thermally or mechanically loaded composites. Therefore Magnesium alloy AZ91 with 15 vol. % γ- Al2O3 fibers as reinforcing phase produced by squeeze casting was thermally cycled between room temperature and increasing upper temperatures. After thermal cycling the amplitude dependence of damping in terms of the logarithmic decrement was measured. Dislocations present in the material turned out to be the main reason for damping. Thermal stresses induced in the investigated composites due to the considerable difference between the thermal expansion coefficients of the matrix and the ceramic fibers create new dislocations on cooling from elevated to ambient temperature. The thermal stresses can achieve the yield stress of the matrix and micro—glide of newly created dislocations as well as their annihilation can occur. Thermodynamic processes in the matrix may influence these effects. The density and arrangement of dislocations may be changed also due to mechanical cycling. Therefore the influence of cyclic bending on the damping behavior of magnesium alloy based MMCs was determined at room temperature. The logarithmic decrement of free decaying vibrations of bending beams as a function of the number of cycles was studied. During cycling damping first increased up to 4×103 cyles stayed more or less constant and decreased again for cycle numbers >106. Like in thermal cycling this behavior can be explained by similar dislocation effects. For numerousness cycles >8×107 the damping again steeply increased with further cycling. With the help of a rheological model developed for crack nucleation and crack growth in unreinforced Magnesium alloy AZ91 this increase could be explained by nucleation and progressing growth of cracks. Relative maxima occurred in this cycling region on the damping versus strain amplitude curves like in unreinforced Magnesium alloy AZ91. Again these maxima can be qualitatively explained and analyzed with the rheological model assuming crack nucleation and crack growth as the source of damping. With increasing numbers of cycles the maximum increased up to fracture of the sample. Cracks in the vicinity of the fractured surface nucleated at fibers or coarse precipitates.