Physics of Metals and Metallography最新文献

Abstract

A sample made from a ribbon of austenitic-martensitic steel 0.3C–13Cr–10Mn–3Si–1V, pre-deformed in the shape of a circular arc with a deflection of 3 mm, was subjected to fast neutron irradiation with a fluence of 6 × 10¹⁹ cm^–2 in the vertical wet channel of the IVV-2M reactor at a temperature of 80°C. This material belongs to the class of stainless manganese austenitic steels with the shape memory effect (SME). Initially, it was expected that irradiation would reduce the SME magnitude after subsequent heating of the studied sample in comparison with the reference one. But instead, the manifestation of SME was revealed already after irradiation, with a decrease in the deflection by approximately 21%. Control experiments confirmed that the lower temperature limit for the manifestation of the SME in this material lies at 120ºC and is absent at 80°C. This allows us to conclude that the effect observed is the result of neutron irradiation.

Abstract

The paper discusses the interaction of components during high-temperature annealing of compressed magnesium and boron powders in the production technology of the superconducting compound MgB₂, based on the results presented in previous works that utilized standard synthesis technology and hot isostatic pressing technology. The study investigates the impact of crystal growth kinetics and diffusion of the components at the phase interface on the morphology of dissipative structures formed during phase transformation. A computer model of binary alloy crystallization was used to analyze the conditions and formation mechanism of dendrite-like structures that arise during the crystallization of MgB₂ from the melt of magnesium (Mg–% B).

Abstract

The technology has been developed for manufacturing the magnetoresistive tunnel junction based on CoFeB/MgO/CoFeB layers with typical lateral sizes in the range from 200 to 700 nm by means of a set of HSQ/PMMA electronic resistive masks. To study the processes of magnetization reversal in the obtained samples, magnetoresistance curves are plotted. It is shown that elements with both vortex and quasi-uniform distributions of free layer magnetization are revealed, which depends on the structure of the magnetosensitive layer and the geometric parameters of the magnetoresistive tunnel junctions. Moreover, the width of the front of magnetization reversal in the elements with quasi-uniform distributions ranges from 2 to 6 Oe.

Abstract

Features of the microstructure of the shape-memory Ti–51 at %Ni alloy subjected to aging at different temperatures are studied. Along with metallographic analysis performed by optical and electron microscopy and X-ray diffraction analysis, room-temperature tensile tests of the mechanical properties are performed. The alloy in the aged state is found to be characterized by the high level of mechanical properties (the ultimate strength is up to 1200 MPa and the relative elongation, 35%) owing to the highly dispersed homogeneous decomposition and the simultaneous strengthening and increase in the plasticity as a result of strain-induced martensitic transformation.

Abstract—Studies of soft magnetic Co-based amorphous alloy AMAG-172 (Co–Ni–Fe–Cr–Mn–Si–B) produced by different manufacturers show that, in the as-quenched state, the nonuniformity of magnetic characteristics across the width of ribbon produced in the PC MSTATOR (Borovichi) is substantially lower. However, the nonuniformity across the ribbon thickness takes place, which favors the formation of bimodal field dependence of the magnetic permeability. The stepped shape of initial portions of magnetization curves in the range of the first maximum of magnetic permeability and intermittent character of the magnetization processes in weak fields allow us to conclude that the formation of the first maximum in the field dependence for the ribbons produced in the PC MSTATOR is related to the independent magnetization reversal of the surface layer. The base layer of the ribbon participates in the formation of the second maximum. In the case of samples manufactured in the JSC NIIMET, the smoothed shape of stepped initial portion of the magnetization curve corresponds to progressive involvement of the base layer of ribbon into the magnetization and magnetization reversal processes. An analysis of hysteresis loops shows that the field bias is related to the interlayer interaction of the surface and the bulk of the ribbon, whereas the formation of asymmetric hysteresis loops occurs with the participation of the second layer with gradual implementation of it into the magnetization and magnetization reversal processes.

Abstract

We demonstrate experimentally that a one-dimensional array of silicon nanowires periodically placed on a nickel substrate enhances the transverse magneto-optical Kerr effect (TMOKE) compared to a nickel film. The enhancement mechanism is associated with the excitation of two types of resonances: multipole Mie resonances in each nanowire and surface lattice resonances (SLRs) emerging from the periodic arrangement of the nanowires. The maximal TMOKE values reached up to 1.9 and 2.6% due to the excitation of SLR and a magnetic dipole resonance, respectively. When the SLR is excited, the spectral width of the TMOKE enhancement is narrower compared to the case of the magnetic dipole resonance.

Abstract

Soft magnetic materials with high magnetic susceptibility in response to the influence of alternating magnetic fields, generate an inductive electric voltage in the receiving coil, the spectrum of which contains higher harmonics. This is due to the nonlinear dependence of magnetization on the magnetic field, and the amplitudes of higher harmonics make a significant contribution to the overall signal if an external field leads to magnetic saturation. Magnetic susceptibility and saturation field are largely determined by magnetoelastic interactions in amorphous ferromagnets, respectively, the amplitudes of higher harmonics should depend on external mechanical stresses. In this work, we study the processes of magnetization reversal in amorphous microwires of two compositions: Co₇₁Fe₅B₁₁Si₁₀Cr₃ and Co_66.6Fe_4.28B_11.51Si_14.48Ni_1.44Mo_1.69 under the action of external tensile stresses. For the first composition, mechanical stresses exceeding a certain limit (higher than 350 MPa) lead to the transformation of the magnetic hysteresis from a bistable type to an inclined one. In this case, a sharp change of the harmonic spectrum is observed. In microwires of the second composition with an initially inclined loop, external stresses cause a monotonous increase in the slope of the hysteresis loop (a decrease in susceptibility). In this case, the amplitudes of higher harmonics change significantly at low stresses, lower than 100 MPa. The results were obtained by magnetization reversal of microwire samples using a system of flat coils, which demonstrates the potential of using these materials as wireless sensors of mechanical stresses with remote reading.

Abstract—Differential thermal analysis, scanning electron microscopy, X-ray diffraction analysis, and microindentation are used to study changes in the structure, phase composition, microhardness, and contact modulus of elasticity of a heat-resistant alloy based on the Ti₂AlNb titanium intermetallic compound, depending on the rate of colling (10–80°/min) from heating temperatures of 950 and 970°С. Using the results obtained, thermokinetic diagrams of high-temperature decomposition of the β(B2) solid solution are constructed.

Abstract

For the first time, an ⁹³Nb NMR study of dichalcogenides Cr_xNbSe₂ (x = 0.33, 0.5) in the paramagnetic state was performed. Analysis of the ⁹³Nb NMR spectra revealed the presence in Cr_xNbSe₂ of three magnetically nonequivalent niobium positions, whose immediate environment contains 0, 1, and 2 chromium ions, respectively. For each Nb position with a different number of chromium atoms in the immediate environment in Cr_xNbSe₂ (x = 0.33, 0.5), the values of the components of the magnetic shift and electric field gradient tensors at the position of the niobium nuclei were determined. Evidence was obtained of the formation in Cr_0.33NbSe₂ of the ordering of chromium ion positions in the ab plane into a (sqrt 3 )a₀ × (sqrt 3 )a₀ superstructure. On the other hand, in Cr_0.5NbSe₂, no obvious indications of the formation of any superstructure of chromium ion positions were found. It has been established that the overlap of the 4d and 5s shells of niobium ions and the 3d orbitals of chromium leads to the appearance of a positive hyperfine field induced by the magnetic moments of chromium on Nb nuclei. From the temperature dependences of the shift and susceptibility in Cr_0.5NbSe₂, an estimate of these induced hyperfine fields is made.

Abstract

The researches of the structural and magnetic properties of the layered chalcogenide Fe₄Co₃Se₈, which has a ferrimagnetic order below T = 196 K, have been performed by means of X-ray diffraction, magnetic susceptibility measurements, and ⁵⁹Co nuclear magnetic resonance (NMR) spectroscopy. It is found that the effective magnetic moment of iron ions is μ_eff ≈ 5.90(5) μ_B. The components of the magnetic shift and electric field gradient tensors at the Co nuclei sites have been determined. The hyperfine field induced on Co nuclei from neighboring iron ions has been estimated from the temperature dependences of the shift and susceptibility in Fe₄Co₃Se₈. It was also established that cobalt ions in Fe₄Co₃Se₈, as well as in the Co₇Se₈ compound, do not have intrinsic magnetic moment, but they do have a moment induced from neighboring iron ions (mu _{{{text{eff}}}}^{{{text{Co}}}}) ≈ 0.36(4) μ_B, which decreases at the magnetic ordering to 0.07(1)μ_B due to mutual compensation of contributions from neighboring iron ions.