Results 1 - 10 of 54407
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[en] Many years and great effort have been spent constructing the microscopic model for the room temperature multiferroic BiFeO3. However, earlier models implicitly assumed that the cycloidal wavevector was confined to one of the three-fold symmetric axes in the hexagonal plane normal to the electric polarization. Because recent measurements indicate that can be rotated by a magnetic field, it is essential to properly treat the anisotropy that confines at low fields. We propose that the anisotropy energy confines the wavevectors to the three-fold axis and within the hexagonal plane with .
[en] Thermally evaporated (Fe 3 nm/Dy 2 nm) multilayers have been magnetically and chemically investigated. Three-dimensional atom probe (3DAP) images related to multilayers revealed diffuse interfaces as well as the presence of Fe in Dy layers. Magnetic hysteresis loops measured on planar layers deposited on flat Si substrates show that the perpendicular magnetic anisotropy is much higher for the multilayers deposited at 600 K as compared to 320 K. 3DAP elemental maps show concurrently that the layered structure is degraded at 600 K. 3DAP analysis concerning an Fe/Dy multilayer deposited at 320 K on flat-topped Si posts is presented, and shows asymmetric interfaces
[en] This paper presents the results of the calculation the thermal field distribution on the surface of processed partunder the influence of a moving heat source (of the low-temperature plasma). (paper)
[en] Operation condition of boilers such as corrosive media, high temperature and pressure has a pronounced effect on quality and performance of its components. Among these, the effect of temperature in microstructure and degradation of mechanical properties of boiler tubes is of most importance. Change in dimension, morphology, chemical composition and carbide spacing are the most important microstructural changes. Methods of study of such changes (through the investigation of composition, carbide spacing and thermal softening) are pointed in this article. Then, a number of failed super-heater tubes of a power plant were microlithography examined. Remaining life of tubes could be estimated by comparison of the results of metallographic and replication tests with microstructural standards
[en] The low-cycle fatigue phenomenon in the framework of plastic deformation is studied considering the temperature parameter. The experimental results obtained for the plastic strain Δεp (1-7%), in the temperature range 20-300 o C are examined. The conclusion is that the lifetime, expressed by the number of stress cycles, Nf, is given by the relation Nf = C exp(-A/T)(Δεp)β+αΔT, where T is the absolute temperature, Δεp is double of plastic deformation amplitude, and C, A, β, and α are material constants. This relation can be interpreted as being the generalization of a relation, known in literature as the 'Coffin-Manson relation', but which does not include the temperature parameter. The validation of this relation can be done either on the results presented in this paper or an those published in literature. (Author)
[en] The temperature dependences of concentration and mobility are investigated in 300–700–300 K thermal cycles at different durations of low-temperature annealing of a ZnSb:0.1 at % Cu sample before the onset of every thermal cycle. Concurrently, the material is annealed for 1500 hours at a temperature difference of 310–670 K, and, then, its thermoelectric parameters are measured. The results are analyzed taking into account the features of the crystalline structure and the covalent nature of the chemical bonds in ZnSb. The operating range and lifetime of this composition are estimated on the basis of a model of the interaction of impurity defects with a decrease in their acceptor activity and an increase in the hole-scattering cross section at low temperatures.
[en] Magnetic nanoparticles dispersed as a ferrofluid with volumetric concentrations in the range 0.4 to 10% and sizes ranging from 59-77 A have been studied via magnetic measurements at room and low temperatures. Remanence measurements have been used to determine switching and coupling effects. Particle size and concentration effects have been investigated and we find that the samples with higher concentrations have larger coercivities than expected due to coupling effects. Interactions have been found to be demagnetising overall as expected for dipolar interacting systems. Surface effects become evident below 10 K when thermal effects are weak
[en] Single- and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s-1. In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.
[en] The texture of the low temperature state is an important state is an important parameter, which is greatly involved in the plastic deformation of polycrystals. In this schema, the first step is to determine the texture of the high temperature state, using various high temperature processes. Unfortunately, the direct determination of the texture of the high temperature phase is not easy and sometimes impossible. This contribution describes an indirect method of determination of this β texture, based on the fact that a grain of the high temperature β phase transforms into different α plates during the phase transformation, where the α plate orientation is correlated with the orientation of the former β grain. The determination of the orientation of the parent β grain is possible, provided that the boundaries of the parent β grain are clear, the number of different plate orientations sufficient, and that a strict orientation relation between the α and β lattices exists. Using this method, the authors have obtained the texture of the β phase of an alloy of TA6V from the determination of the orientations of a population of parent β grains, the orientation of a given β grain, deduced by correlating the orientations of the corresponding α plates measured by E.B.S.P