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The new method of time-averaged speckle images and the well-known method of speckle-field interference studied the development of plastic deformations occurring during multicycle fatigue of structural steel. The correctness of strain determination by the new method is evaluated by comparing the data obtained by the two methods. Two optical systems including laser modules with different wavelengths were investigated. The proposed optical system allows to determine the components Δuy, Δuz of the relative displacement vector of two surface points located at a distance (measurement base) Δs = 66 μm. The known scheme makes it possible to describe deformations by the traditional method on the base of 470 μm. The object of study was a flat specimen made of 09Г2С steel with two side notches. Fatigue tests were carried out on a resonance-type machine at different cycle amplitudes. It is shown that at all cycle amplitudes the development of plastic deformations occurs by the mechanism of cyclic creep. There is a good correlation between the data obtained by two different speckle methods. At the same time, the strain estimated by the new method is in some cases an order of magnitude higher than the strain calculated by the known method. Obviously, this is due to the existence of local smallsized (of the order of 101 μm) strain areas which cannot be measured by conventional methods. The ultimate tensile strain Δuy/Δs calculated by the new method is of the order of 10–1, which coincides with the similar strain occurring in tensile testing of standard specimens. The results obtained by the new method justify the need of developing sensors and nondestructive testing devices of a new generation, allowing to estimate the time to fatigue crack initiation by the rate of change of physical quantities and by their limit values.

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones.

The effect of a high magnetic field up to 12 T and a high hydrostatic pressure up to 12 kbar on the stability of the metamagnetic isostructural phase transition and the multicaloric effect of Fe49Rh51 alloy has been studied. The phase transition temperature shifts under the magnetic field and the hydrostatic pressure on with the rates of dTm/μ0dH = −9.2 K/T and dTm/dP = 3.4 K/kbar, respectively. The magnetocaloric and multicaloric (under two external fields) effects were studied via indirect method using Maxwell relations. The maximum of the entropy change is increasing toward the high temperature region from ∆S~2.5 J/(kg K) at 305 K to ∆S~2.7 J/(kg K) at 344 K under simultaneously applied magnetic field of 0.97 T and hydrostatic pressure of 12 kbar. The obtained results were explained using the first-principle calculations of Gibbs energies and the phonon spectra of the ferromagnetic and the antiferromagnetic phases. Taking into account the low concentration of antisite defects in the calculation cells allows us to reproduce the experimental dTm/dP coefficient.

The bi- and tri- layered magnetoelectric composites were fabricated from magnetic Fe49Rh51 and piezoelectric PbZr0.53Ti0.47O3 materials. It was shown the electric field-induced stresses reduce the magnetization around magnetic phase transition temperature of Fe49Rh51: by 5.4% for tri-layer PZT/FeRh/PZT composite and by 3.6% for bi-layer FeRh/PZT composite. The magnetoelectric properties were studied at 320 K, the magnetization rate was estimated for the magnetic field of 0.5 T. The heterogeneous distributions of stresses and magnetization in volume of magnetic layer under applied magnetic and electric fields were demonstrated using COMSOL Multiphysics software. The obtained results demonstrate the tri-layered composite is more effective for tuning the magnetization

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones. [ABSTRACT FROM AUTHOR]

Direct studies of the adiabatic temperature change (ΔTad) in the Ni47Mn40Sn12.5Cu0.5 Heusler alloy in steady magnetic fields up to 8 T by the extraction method and in pulsed magnetic fields up to 50 T were carried out in this paper. The alloy Ni47Mn40Sn12.5Cu0.5 demonstrates a magnetostructural phase transition (MSPT) of the first order in the 254–283 K temperature range as well as a second order phase transition near the Curie temperature TC = 313 K. An inverse magnetocaloric effect (MCE) was found in the region of the MSPT, and it reaches the maximum value ΔTad = −12 K in 20 T at the initial temperature T0 = 275 K. The irreversible part of the MCE reached ΔTir = −10 K when the field is completely removed. We consider the dynamics of the MCE in the vicinity of the MSPT and discuss the mechanisms that cause the giant irreversibility of the MCE as well as the possibilities of its application in hybrid cooling systems. [ABSTRACT FROM AUTHOR]

Samples of composites with different porosity and surface roughness based on LaFe11.4Mn0.3Si1.3H1.6 (LFMSH) alloy powders were obtained, their magnetocaloric properties were studied by the direct method in cyclic magnetic fields of μ0H = 1.2 T with a frequency of 2 Hz. The maximal value of the adiabatic temperature change in pure LFMSH powder was ΔT = 3 K at T0 = 287 K in the sample cooling regime, and for composite samples, this value was approximately two times lower than that in the powder. The effect of Mn and H atoms on the electronic structure and local magnetic characteristics of the initial La(Fe,Si)13 alloy was studied using electron density functional theory. Replacement of some Fe atoms with Mn reduces the total magnetic moment and somewhat lowers the Curie temperature. In contrast, hydrogenation leads to an increase in exchange interactions between Fe atoms located at the vertices of the icosahedron and an increase in the Curie temperature. [ABSTRACT FROM AUTHOR]

In this paper, we focus on understanding the magnetic field and temperature dependences of the heat capacity CP, electrical resistivity ρ, and magnetocaloric effect ΔTad in Fe48Rh52 alloy near room temperatures. The phase diagram is constructed according to the CP(H, T) and ρ(H, T) data, and the field shift of the critical temperature is found to be 9.6 K/T. The experimental results on the heat capacity do not confirm the existing assumption about the electronic nature of the antiferromagnet–ferromagnet phase transition in the FeRh alloy. An increase in resistance through the ferromagnetic–antiferromagnetic phase transition is explained by a sharp decrease of the carrier density and simultaneously the appearance of an additional conducting channel. The adiabatic temperature change ΔTad at a field change of 1.8 T equals −9.8 K, and the maximum value of the entropy change ΔS estimated from CP(H, T) and ΔTad(H, T) data is equal to 12.8 J/kg K. The differences in the magnetocaloric effect values in the heating and cooling run in weak magnetic fields are explained based on the thermal expansion data. An almost reversible degradation of the magnetocaloric effect was discovered upon the continuous application of a cyclic magnetic field at temperatures near the magnetostructural transition. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect in the Fe49Rh51 alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe49Rh51 was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s−1, 770 T s−1), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate. [ABSTRACT FROM AUTHOR]