Physics of Metals and Metallography最新文献

An alloy with a nominal composition of Mn₅₅Al₃₆Ga₉ is prepared by four different methods which ensure different cooling rates. Two bulk samples are prepared by induction melting followed by water quenching from a homogenizing temperature of 1100ºС; one of the samples was sealed in a quartz ampoule and subjected to water quenching, whereas the other sample directly was subjected to water quenching. Two samples are prepared in the form of ribbons by quenching from the melt on a rotating copper wheel at linear speeds of 10 and 40 m/s. Thus, samples quenched at different rates are prepared. For these samples, regularities of phase transitions occurred during heating are determined, and difference in the regularities for the bulk and rapidly quenched samples are found. Based on the data obtained, we make an assumption that the γ₂ → τ phase transition has features of a bulk transition. Magnetic hysteretic properties of the rapidly quenched ribbons are measured. The high thermal stability of the rapidly quenched ribbons alloyed with gallium is shown.

Abstract

The commercial Ti–6Al–4V alloy was obtained in an almost single-phase state, formed by finely dispersed globular α-grains with an average size of 12 μm, using thermomechanical processing, including hot rolling. The microtexture and structure of the alloy were studied using X-ray diffractometry and transmission and scanning electron microscopy, including orientation microscopy. It is found that for α-grains the Burgers orientation relationships are satisfied, and twin orientations are ensured in the rolling plane. A significant scattering of the crystallographic orientations of α-grains relative to each other (up to 10°–15°) is established for each group of close Burgers orientations as a result of plastic deformation by rolling at high temperatures. Clusters of microtexture regions in the layered microstructure of grains and the formation mechanisms and mutual crystallographic misorientations of microtexture regions and grains in the alloy have been identified.

Abstract

The electrical resistivity of 12Х18Н10Т stainless steel specimens was measured in the course of compression and heating under stepwise shock compression. A mathematical simulation of the obtained experimental data was conducted. The simulation allowed switching to specific values and reconstructing the volume–temperature dependence of the electrical resistivity of steel at high pressures of 25–65 GPa and temperatures of 350–950 K. Semi-empirical regularities were identified that permit the prediction of the total effect of a decrease in the electrical resistivity of 12Х18Н10Т steel upon compression and its increase upon heating. The outcomes of the electrical resistivity tests on shock-compressed and heated steel are evaluated in comparison with the existing literature data on similar experiments conducted under atmospheric pressure and high temperatures.

Abstract

The investigation is focused on the impact of hydrogen on the physical and mechanical properties of 316L austenitic stainless steel (67.5Fe, 17.7Cr, 10.6Ni, 2.6Mo, 1.2Mn, 0.4Si in wt %) processed by selective laser melting (SLM). The study also determined the kinetic parameters of hydrogen interaction with 316L‑SLM steel at temperatures ranging from 300 to 700°C. It has been demonstrated that the plasticity characteristics are highly sensitive to the impact of hydrogen within the temperature range from 20 to 600°C. At 600°C, the maximum degree of hydrogen embrittlement is ≈30%. However, the elongation to failure and reduction of area remain at a sufficiently high level. Reduction in strength characteristics is only observed at 600°C and does not exceed 10%. Prolonged thermal impact and resulting structural changes do not affect the kinetic parameters of hydrogen interaction with 316L-SLM. The hydrogen solubility in SLM-processed 316L steel and 12Cr18Ni10T steel produced by conventional technology is nearly identical.

Abstract—

The study is devoted to the theoretical analysis of noncollinear magnetic structures of charge-ordered manganites with a doping level of x = 3/4, 4/5. The reasons for canted and perpendicular magnetic structures to form as a result of the competition between the orbitally dependent exchange interactions in different crystallographic directions and the influence of single-ion anisotropy are considered. The mechanism of formation of predominantly noncollinear magnetic structures is shown. Trimer stripe magnetic structures with ordering along pseudo-perovskite axes x_p, y_p, z_p = b are predicted. The presence of magnetic structure components aligned with the b axis is assumed and methods for checking the presence of such components based on field dependencies of magnetization and antiferromagnetic resonance frequencies are proposed.

Abstract

The solid thin films of Py/Pt and Py/W heterostructures have been studied using the ferromagnetic resonance method. The temperature dependences of the Gilbert damping parameter and voltage of the inverse spin Hall effect (ISHE) have been obtained in the 5–290 K temperature range. An abnormal increase in the Gilbert damping parameter in the vicinity of 50 K and a change in the voltage of ISHE has been found. It has been concluded that an increase in the Gilbert damping parameter is of spin-orbital nature.

Abstract

A study has been conducted on the hydro-vacuum dispersion process of metal melts using gray cast iron SCh20 (in Russian nomencluture; 3.3–3.5C, 1.4–2.4Si, 0.7–1Mn, <0.15S, <0.2P in wt %)—an analogue of GG20. It has been revealed that the main factor conditioning the mechanoactivation of formed particles is their solidification in a fibrous non-equilibrium structural-tensioned state. This state is achieved by flattening and asymmetric twistedness of droplets that are detached from the liquid metal in the disperser under volumetric impact of shock-pulsating waves of hydraulic discharge. The degree of particle activation was found to depend exponentially on their dispersion and specific surface area. These parameters determine the degree of asymmetry of shear deformations and the amount of accumulated energy. In turn, the size dispersion and specific surface are significantly influenced by physical and technological factors such as the specific flow rate and pressure of injected water, the thickness and the elevation angle of the hydro shell of the vacuum diffusion funnel, the diameter of the dispersed melt jet passed through it, and its superheating temperature. The control of these parameters makes it possible to smoothly adjust the key ratio “liquid metal: water” and set up the dispersion process with the highest possible degree of size dispersion and activation of the resulting powder.

Abstract—

The features of magnetic microstructure of La_0.73Dy_0.27Mn₂Si₂ at 293 K have been visualized by atomic force and magnetic force microscopy. Magnetic force images reveal the presence of low-contrast magnetic domains. The change of Raman spectral characteristics of light scattering in the process of cooling La_0.73Dy_0.27Mn₂Si₂ to a temperature of 263 K is experimentally detected. The electronic structure of La_0.73Dy_0.27Mn₂Si₂ is investigated by resonance photoemission spectroscopy with the use of the synchrotron radiation. Resonances at the 3d and 4d levels of electronic structure show different properties of valence electrons. Using the Dy 3d–4f (M_4.5 absorption edge) resonance, the distribution of 4f states of dysprosium in the valence band is determined. Photoemission upon the giant Dy 4d–4f (N_4.5 absorption edge) resonance is determined by the contribution of all states in the valence band due to the sudden involvement of the Coulomb interaction. The energies of the 5p and 4f levels of La, the 4f level of Dy, and the 3d level of Mn in the valence band are determined.

Abstract

The study examines the behavior of vortex-like magnetic inhomogeneities that arise in a ferromagnetic disk with spatially modulated uniaxial anisotropy under magnetic fields of varying orientations. The research identifies the characteristic remagnetization stages of the vortex-like inhomogeneities formed in the region of the defect. Critical fields of their rearrangement are found and an explanation is given for the difference in the behavior of these inhomogeneities in perpendicular and planar magnetic fields. The effect of the helicity of the magnetic skyrmion localized at the defect on its remagnetization process in the planar field is revealed.

Abstract

The kinetics of recrystallization of pure iron deformed by high pressure torsion at 20 and 250°C has been studied in the course of annealing at 450°C. The change in grain size upon annealing at 450°C does not obey the law of normal grain growth, either in iron with an SMC structure formed at 20°C or in iron with a dynamically recrystallized structure formed at 250°C. This is because new thermally activated recrystallization centers appear upon annealing. The study has also established the influence of deformation temperature on the annealing texture. In the course of annealing, after deformation at 20°C, the material develops a sharper texture with a predominance of two components, {110}〈111〉 and {110}〈001〉. Similarly, after deformation at 250°C, a sharper texture with a predominance of three components, such as {110}〈111〉, {110}〈001〉, and {112}〈111〉, is formed.