Solid State Phenomena Vol. 137

Abstract: The mechanical and fatigue properties of Cu - Al - Mn shape memory alloys with different phase fractions at room temperature were investigated. The specimens with different chemical compositions (Al: 8.9 - 12.5 wt. % and Mn: 3.3 - 9.3 wt. %) were tensile loaded with 10-3 s-1 tensile strain rate. Austenitic specimens have the highest tensile strength and fracture strain. Yield strength, tensile strength and elongation of martensitic alloys were lower compared with austenitic alloys. Fracture strain of martensitic alloys depend only little on the chemical composition. Specimens of martensitic, austenitic and three different multiple phase specimens were tested in the high cycle fatigue range at room temperature. The Woehler curves for multiple specimens depend on the phase fraction at testing temperatures. Different elements as Co, Ni, Fe and Si were alloyed to CuAl11.6Mn5. All decreased the ductility of the specimens, and their fatigue properties. Maxima could be detected in the strain amplitude dependence of damping for multiple phase specimen. These maximum are shifted to lower damping and to higher strains with increasing number of mechanical cycles, compared to the as cast condition for not cycled specimen. The strain amplitude dependence of damping in martensitic and austenitic Cu – Al – Mn shape memory alloys does not change much during mechanical cycling.

Abstract: The ductility of Cu – Al – Mn shape memory alloys at room temperature depends on the aluminium content. High aluminium contents make Cu – Al – Mn very brittle and unsuitable for plastic shaping. Two Cu – Al – Mn shape memory alloys were investigated. The ductile alloy CuAl7.8Mn9.5 (all contents in wt. %) could be easily cold rolled by 86 %. The alloy CuAl12Mn4.3 could be cold rolled by only 12 - 14 %. The amplitude dependence of damping of austenitic specimens increased with increasing degree of cold work, whereas the damping of martensiticaustenitic specimens decreased. These observations can be explained by the creation of stress induced martensite and therefore by new moveable interfaces like phase- and twin boundaries, which contribute to damping. Plastic deformation increases the dislocation density, too. Both the increase of dislocation density and the increase of martensite content can lead to a decrease of damping mainly for high deformation degrees. Same shape memory alloys have shown negligible hardness increase during cold rolling, too. This behaviour, untypical for metals, can be explained by the generation of new martensite and by the fact that the hardness of martensite is smaller than the hardness of austenite. Some aging effects of the specimen after cold rolling, which lead to decrease of damping, were detected. This can be explained by pinning of moveable interfaces by point defects and/or retransformation of martensite into austenite.

Abstract: Spinodal decomposition of solid solution in the 60 at.% Mn - 40 at.% Cu alloy was observed at the temperatures of decomposition (380 – 420 °C) using the neutron diffraction method in situ. The contribution of residual stresses of third type introduced by further cooling of alloy and, correspondingly, martensitic tranformation is estimated. The relatively small value of stresses of third type introduced by martensitic transformation is revealed. Appearance of magnetic superstructural reflexes typical for antiferromagnetic ordered structure is noted.

Abstract: The simultaneous influence of both thermal and mechanical treatment was applied to produce a geometrically complex shaft from 51CrV4 steel. This special treatment led to the formation of adjacent microstructures which were significantly different from each other. It was found that these microstructural changes were accompanied by a change of mechanical properties in terms of hardness, electrical resistivity and especially internal friction. Specimens for structural studies and study of mechanical and physical properties were taken out from different places of the produced shaft and tested in order to verify and understand the obtained gradation. The significant variations in properties could be explained in terms of structure and dislocation behaviour under applied cyclic stress using mechanical spectroscopy technique. The cold-work (Snoek-Köster) peak was recognised and analysed in the structure of this steel.

Abstract: Study of anelasticity in AZ31 magnesium-based alloy in initial (hot-rolled at 370 оС) condition and after one and four passes of equal channel angular pressing is carried out. An internal friction peak was found at 170 °C at a frequency f of about 1 Hz. Two possible mechanisms of this peak are discussed: it is suggested that the peak origin is the grain boundary relaxation.

Abstract: Thin layers of the OLED related polyphenylene-vinylene (PPV) deposited by a precursor on micro-fabricated Si cantilevers were studied by applying the vibrating-reed technique during repeated temperature cycling between 100 and 520 K. By means of the Langmuir-Blodgett method for film production, the dependence of damping and elastic modulus on well defined values of film thickness (16 to 69 nm) was determined. Simultaneous measurements of these quantities showed four damping peaks during heating around 130 K (called γ), 250 K (β), 350 K (β’), and 400 K (called C). Three of them (γ, β’, C) disappeared after heating to the highest temperature (520 K) indicating their presence in the precursor only. The activation parameters of the relaxation peaks (γ, β, β’) were estimated and assigned to specific atomic movements in the molecule. Peak C occurs during the conversion process of precursor to polymer. Earlier results are essentially substantiated, indicating only slight differences to those for layers produced previously by spin coating. The observed thickness dependence of damping for the γ and β peaks suggests a weaker contribution of molecules in the surface region than of those in the bulk, while the β’ peak is supposed to result from molecules in the interface region between layer and substrate.

Abstract: The work is devoted to the problem of role of ambient factors (external electromagnetic field, in particular) in the process of ageing of mechanically burden nonmetallic solids (rocks). A specific research point is the effect of temporary activation of Acoustic Emission (AE) of rocks specimens during action of EM field pulses applied externally. Extended experimental studies of responses of AE have been conducted to evince the changes in defects accumulation process in loaded specimens due to external power impacts (EPI). The experiments have been held on noiseless rheological machines available at Bishkek Geodynamic Research Center - RS RAS. We have tested a number of specimens made of different materials and analyzed the temporal dependence of AE activity during exposure in electric field and crossed electric and magnetic fields; the compressive load being constant. The effect of AE stimulation by power pulses (triggering) has been verified. The obtained results allow to distinguish two kinds of AE activation. The first kind involves simultaneous well correlated growth of numbers of minor and major AEs (so-called selfconsistency of temporal plots of activity of different range acoustic events). The second kind represents dissimilar variations: the increment of activity of minor energy AEs, but the decrement of those of major energy. The first kind of solids material responses to EPI is prevailing when the compressive loads is under 0,85 of fracturing value. The episodes of dissimilar AE responses may signify that electromagnetic control of defects accumulation process inside rocks is possible, in principle.

Abstract: We propose a model for explanation the “domain-wall” type configuration states in binary lipid mixtures of cationic and neutral lipids, associated with observed relaxation effects in their aggregates. We apply the analogy with formation of Kibble-Zurek topological defects, which we suppose connected with structural dynamics of the lipid phases. In frames of the proposed model, the density of kink-type defects and the energy of the configurations are calculated.

Abstract: Characteristic low-temperature mechanical loss peaks are reported in cold-rolled steel sheets. Similar mechanical loss peaks are observed in both metallic and paper substrates covered with thin oil films. The surface induced origin of these peaks is elucidated through direct comparison of mechanical loss peaks observed in the as-received, cold-rolled samples with loss peaks observed in metallic and paper substrates covered with thin films of the arachis oils. In all of these instances, similar low-temperature mechanical loss peaks are observed in the temperature range from 180 K up to 300 K in both low-frequency resonant and low-frequency sub-resonant mechanical spectrometers. It is concluded that low-temperature mechanical loss peaks are generated by surface induced effects that arise from the oil film itself.

Abstract: A brief historical review of scientific research in the field of anelasticity in solids carried out during the last 50-70 years in the USSR, Russia and states of CIS is given.