This article reports an computer simulations of physical properties of Heusler NiMnGa alloy. Computer simulation are
devoted to austenite phase. The chemical composition of researched specimens causes generation martesite and austenite
phases.
In this paper we present results of the investigation of polycrystalline Ni52,2Mn21,3Ga26,5 alloy before and after homogenisation
at 1173K processed for different time intervals. We investigated the influence of duration of homogenisation on
kinetics of reversible martensitic transformation (RMT). In order to present changes of kinetics of RMT, thermal hysteresis
was determined based on calorimetric (DSC) investigation. Our results suggested that thermal annealing at 1173K
caused plastic deformation of crystal lattice in the investigated alloy.
The functional properties of crystals have been described by the thermodynamics potential of a crystal. This potential
usually is presented as matrix, the elements of which represent physical properties of crystals. Using the partial
derivatives we can obtain some physical properties of crystals. In the experimental part of article the results of study of
some functional properties of a ferroelastic monocrystal of molybdate (III) gadolinium (VI) are presented.
In the article the results of diffractometric, calorimetric research as well as the chemical constitution have been presented.
The research was carried out on the samples made of a thin amorphous tape made with the melt-spinning method
from the alloy revealing the memory Ti50Ni25Cu25 effect. The samples were subjected to annealing at different parameters
of holding in temperature. After the heat treatment, the response of martensite transformation and formed crystal structures
has been observed. The X-ray microstructural tests showed forming so-called outer (top) "free" layer of lamellar
precipitation of the high level of coherence.
Functional materials, of which an example is ferroelectric, ferroelastic monocrystal of molybdate (III) gadolinium (VI),
are often used in the micro-motor operators (micro-servo motors) working in changeable environment conditions. Most
frequently this change refers to temperature. That is why the important practical problem is the precise measurement of
the value of piezoelectric tensor elements in dependence on the temperature of a particular monocrystal. In the presented
article for this kind of measurements, the use of X-ray diffractometer has been shown. The advantage of the method presented
is that, apart from precise dependence measurement between the temperature of a monocrystal and the value of
piezoelectric tensor elements, it enables synchronous measurement of the value of thermal expansion tensor elements for
a monocrystal.
The work deals with the evaluation of surface geometry of a 50H-grade-steel-surface layer which was multiple melted using a laser. The surface roughness of the layer was analyzed as a function of the laser treatment parameters and the trajectory of beam motion. The experimental design method and the statistic program were also applied for functional description of the analyzed dependences. As results, an increase in the surface smoothness and microstructures responsible for high hardness were achieved due to appropriate combination of treatment parameters. The paper is illustrated with the surface-roughness-profile plots.
The measurements of shape memory effect of the Ti50.08Ni49.92 alloy were conducted by observing the progressive changes in shape recovery with increasing number of thermo-mechanical cycles. Two different thermo-mechanical protocols were studied using a bending apparatus. In the first one, the temperature cycling was performed under bending deformation for cooling and subsequent heating without external load. After each heating path the shape recovery was evaluated as a result of reverse transformation. In the second protocol the temperature cycling was executed under bending deformation both for cooling and heating. Here, the shape recovery was measured under load and as the load was
released right after heating. The results for the second protocol showed that the degree of shape recovery decreases continuously with thermo-mechanical cycling while in the first protocol it is observed to be high almost stable. It was found that the changes in shape recovery behaviour depend on the nature of the transformation cycle, in particular, on whether a stress is applied during transformation. The reverse transformation in the second protocol occurred under load; therefore, such a loading process may inhibit to some extent the shape recovery by an uncompleted transformation (retained
martensite). The results also suggested that the microstructural changes in the actuated material are more pronounced for the thermo-mechanical cycling where the load was maintained during both cooling and heating in comparison to the cycling with heating under no load.
From literature data it can be concluded that physical properties of the amorphous alloys depend on the type of chemical composition. Further modification physical properties of these alloys can be achieved by a proper heat treatment process and structural changes of material. In the paper the experimental results of the Fe97.45Si2.55 amorphous alloy are presented with major attention to determine an influence of isothermal annealing (various temperatures and time periods) on the changes of selected structural parameters in the process of primary crystallization. Hence, lattice constant of crystallized phase, α, root-mean-square micro-strains, RMS, and coherent block sizes, D, were established as the structural parameters. These structural characteristics were determined using an X-ray analysis. As a mechanical parameter, we considered a micro-hardness of the heat treated alloy.
In this paper the influence of work parameter of magnetic force microscopy (MFM) on the magnetic contrast of the stray field measured in soft magnetic amorphous Fe-based ribbons using two-pass technique has been analyzed. It was proved that an increase in ΔZ separation of sample-tip during the second scan affects considerably the quality, contrast of obtained micrograph of the stray field image. Increase in &ΔZ causes smaller interaction between the cantilever's tip and tested field. It is caused by smaller influence of the source field emitted from the sample on the magnetic tip. Detirioration and contrast's broadening of obtained pictures allows to analyze and detect the areas which have positive as well as negative magnetization.
Shape memory alloys (SMA's) have become one of the major elements of intelligent structures and mechanisms (e.g. sensors, actuators, and active biomaterials) due to their unique thermo-mechanical properties. The main features of SMA's are related to a reversible martensitic transformation that can be induced either thermally or by applying stress. In this study, crystalline structure and changes in phase composition of TiNiCu samples were investigated mainly using an X-ray diffraction (XRD) method. Amorphous ribbons with the composition of Ti50Ni25Cu25 were characterized under various temperatures during annealing. Changes in crystalline structure have been shown to be dependent on the executed processes. XRD measurement results revealed that heat treatment annealing yields totally the crystalline structure of amorphous structure and martensite is the major phase.
Bi-substituted ferrite garnet (R Bi)3(M FE)5O12 epitaxial films with anomalously high (up to 1.2 deg/μm at RT) specific Faraday rotation provide a unique possibility of magneto-optical imaging of magnetic field microdistributions with a sub-micron resolution close to the diffraction limit. In the present work we give a detailed description of the physical principles and various applications of such films in materials science, microelectronics, magnetic testing and nondestructive evaluation (NDE) of defects in both ferromagnetic and non-ferrous metal components. In the latter case eddy-current excitation is used to reveal flaws, cracks and corrosion. The technique is ideal for not only detailed inspections, but also for rapid scanning over large areas to quickly determine structural condition of the part.
Structural characteristics of the austenite phase of a NiTi shape memory alloy (SMA) subjected to thermo-mechanical cycling under a constant applied load were studied. Progressive thermo-mechanical action of the external deformation results in both changes of the defect structure and, macroscopically, in memory shape effect degradation. The study was performed using the x-ray method of analysis. Two parameters have been determined to study the evolution of the austenite phase: root-mean-square (RMS) microstrains and coherent block size. the number of thermoa-mechanical loading cycles was varied either from 50 to 400 (for series) or from 1 to 5 for preliminary estimates. Experimental results show that the loading process depends on the changes in the structural cahracteristics. On this basis we propose some structural parameters helpful in the prediction of the memory shape effect degradation in the actuated SMA materials.
In this paper the experimental measurement results of the residual stresses in shape memory alloys (SMA's) are discussed. The experimental data are based on the investigation of the changes in root-mean-square (RMS) micro-strains and size of coherent blocks. The study was performed on the samples of Ni50,6Ti49,4 alloy that were subjected to cyclic thermo-mechanical loading. To induce reversible martensite transformations in the material, the external loading was used with subsequent data recording using x-ray method. The results of experimental measurements of the RMS micro-strains and coherent block sizes in austenite phase are presented. Based on the experimental data the computer simulation results are presented. Experimental and theoretical results have shown that the changes of structural parameters can be helpful for evaluate of functional characteristics of NiTi alloys.
This paper includes the results of experimental investigation and calculations of changes in residual stresses in NiTi shape memory alloys. For this purpose, the test of thermal and mechanical loading on the samples of Ni50Ti50 was performed. One-way and two-way shape memory effects were observed during loading and heating, i.e. SME alloy can be deformed, then recover its original shape when heated to a certain temperature. After this experiment the investigation using X-ray method was performed. In our experiments we used X-ray diffraction of the austenite phase of NiTi at room temperature to investigate the changes of elastic fields during thermal and mechanical loading. Diffractometer data were used for calculations of residual stresses. Root-mean- square (RMS) strains and sizes of coherent scattering regions were calculated using harmonic analysis. Based on the experimental data, the modeling results are depicted. Computer simulation takes into consideration martensite transformations, twinning, elastic and irreversible deformations. The result of thermal and mechanical loading and computer simulation provide data for shape memory alloys behavior under cyclic loading.
It is possible to estimate reliability of the materials during their use by recording the changes in defect density of polycrystalline structure, which can be estimated on residual stresses at a crystal micro-level. In this paper the experimental measurement results of the residual stress field changes in actuator manufactured using shape memory alloy (SMA) are presented. The experimental data are based on the investigation of the changes in the root-mean-square (RMS) micro-strains and size of coherent block in the SMA caused by thermal and mechanical loading. The study is performed on the samples of approximately equiatomic TiNi alloy. To induce the reversible martensite transformations in the material the external loading is used with subsequent data recording using the X-ray method. The results of experimental measurements of the RMS microstrain and coherent block size in austenite are presented. Based on the experimental data a novel mathematical model is proposed, which is used in the computer simulations that include the martensite transformations, twining, elastic and irreversible deformations. The experimental and computer modeling results of stress and strain field generated by the defects in polycrystalline materials are discussed.
The durability of materials realizing shape memory effect testifies that the accumulation of defects of a crystal structure in this process occurs more slowly in comparison with irreversible deformation. The attempts were undertaken to simulate process of generation of a field of stresses in process of martensite transformations, but they did not prove to be true by experimental data. In offered work the attempt of an experimental research of a residual field at a structural microlevel is undertaken. Meaning complex phase structure interfering to a choice of two orders reflection from family of planes or frequently even of two peaks from one phase, as a first approximation investigated root-mean-square (RMS) microstrains and coherent block sizes analyzing one diffraction peak. In case of necessity used also separation of the overlapped peaks of different phases.
In the paper an opportunity to initiate martensite transformation under ultrasound action is shown. The mathematical model for calculation of this effect has been applied.
In our paper an opportunity to initiate the shape memory effect (SME) with the help of ultrasonic vibrations (US) is shown. Influence of an ultrasound on the plastic deformation of the NiTi-wire under the action of a one-directed stretching is investigated. The behavior of the 'nitinol' is shown when T approximately equals Ms different from Langenecker's effect.
Residual stresses evolution in plastic deformation process of aluminum alloy and 18.8 steel was studied by the x-ray method. The measurements were carried out on two structural levels. The tensor character of macrostresses and RMS (root-mean-square) microstrains was demonstrated experimentally. On this basis a mathematical model of the process is proposed. The model proposed was used for the study of the residual stress evolution in the shape memory alloys.
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