Vol 124, No 8 (2023)

Molecular dynamics (MD) simulations were applied to study radiation damage formation in collision cascades created by the recoil of primary knock-on atoms (PKA) with PKA energies Epka = 5, 10, 15, 20 and 25 keV in α-Ti at temperatures T = 100, 300, 600 and 900 K. A series of 24 collision cascades with the same set of (Epka, T) parameters has been simulated to generate representative sampling. Sapling size was justified a posteriori. The number of Frenkel pairs Nfp and cascade relaxation time were obtained as functions of (Epka, T). It was shown that the average ⟨Nfp(Epka,T)⟩ fits within 0.3NRT, provided the threshold displacement energy is chosen in 28-40 eV range depending on the irradiation temperature. Under high PKA energy/low irradiation temperature conditions, displacement cascade region splits into subcascades expended along high-energy recoil trajectories. Cascade relaxation time does not depend on Epka in this case. Contrary, under low PKA energy/ high temperature simulation conditions, most of collision cascades possess equiaxial shape, and their relaxation time grows with PKA energy increase.

The paper describes an ultrasonic method for the formation of locally deformed zones (LDZ) in the form of mechanical scratches applied to the surface of anisotropic electrical steel of nuclear power plants to crush its domain structure in order to reduce the total magnetic losses Р. It is shown that, as a result of such processing, using the example of a 3407 type steel, the value of P decreases by an average of 10-15%. It has been established that exposure to ultrasound leads to a significant increase in the rate of scratching.

The magnetization processes nonuniformity of an amorphous cobalt-based soft-magnetic alloy AMAG-172 (Co-Ni-Fe-Cr-Mn-Si-B) in the as-quenched state were studied. Studies have shown that the main reason of the magnetic characteristics and magnetization processes nonuniformity is the nonuniformity of internal stresses due to the alloy manufacture method. An indirect characteristic of internal stresses is the domains volume with orthogonal magnetization. The observed bimodal field dependence of the magnetic permeability and the field shift of the hysteresis loops in the region of 180-degree domain walls displacement are a consequence of the nonuniformity of the alloy over its thickness. The field shift and the asymmetry of hysteresis loops are explained in terms of the formation of a unidirectional exchange anisotropy at the interface between the ferromagnetic and antiferromagnetic phases of the planar magnetization components oriented along the ribbon axis. The field shift disappearance and the asymmetry of the hysteresis loops along the width of the tape can be interpreted as a decrease in the thickness of the CoO oxide antiferromagnetic layer due to the difference in the concentrations and depth of oxygen and hydrogen atoms penetration induced into the surface of the tape during the manufacture of the tape as a result of interaction with atmospheric vapor.

In this paper, the structural and magnetic properties of layered nanowires (NWs) made of alternating layers of nickel and copper were investigated. NW arrays were obtained by matrix synthesis. The nickel layers had a fixed thickness of 400 nm, and the thickness of the copper layers varied from 25 to 300 nm. The magnetic characteristics of such NWs were studied in two states: in a matrix (integral magnetic characteristics determined using vibrating sample magnetometry) and for individual NW (local magnetization visualized using MFM). For NWs in the matrix, the hysteresis loops measured for the two directions of the magnetic field become identical when the thickness of the Cu layer increases to 300 nm, which is due to the weakening of the dipole interaction between the Ni layers. The coercive force (190 Oe) and the residual magnetization (0.32 Ms) in the parallel direction of the field are maximal for the thickness of the Cu layer equal to 100 nm, which corresponds to the diameter of NWs and the distance between them. The MFM method was used to study samples with Cu layer thicknesses of 300 nm. It is demonstrated step by step how the application of an external magnetic field leads to remagnetization. An intermediate antiparallel distribution of magnetization in neighboring layers is revealed. The magnitude of the coercive force for an agglomerate of two or three NWs varies between 40-50 Oe, but the magnetization switching field turns out to be about 160 Oe, which is comparable to the coercive force for an array of NWs of this type (180-190 Oe). This demonstrates the role of the NWs' dipole interaction in the matrix.

Symmetric and three asymmetric tilt grain boundaries Ʃ 5 in niobium have been studied by computer simulation methods. The structure and energies of the boundaries under consideration, as well as the energies of the formation of point defects in them, are calculated by the method of molecular-static modeling. The dependences of the formation energies of point defects on the distance from the plane of the grain boundary are analyzed. Using the method of molecular dynamics, the coefficients of grain-boundary self-diffusion for the considered boundaries are calculated.

Microhardness and electromagnetic characteristics of corrosion-resistant chromium-nickel (wt. %: 16.80 Cr; 8.44 Ni) austenitic steel subjected to electron beam plasma carburizing at temperatures of 350 and 500°C, frictional treatment with a sliding indenter and combined treatments, including frictional treatment and plasma carburizing have been investigated. It has been found that plasma carburizing increases the microhardness of the steel surface from 200 to 1100 HV0.025. The total hardening depth was 25 microns after carburizing at T = 350°C and 300 microns after carburizing at T = 500°C. Frictional treatment increases the microhardness of the steel to 600 HV0.025 with a total hardening depth of 500 microns. It has been shown that the diffusion-active layer with a dispersed structure formed during preliminary frictional treatment contributes to additional hardening of the steel (up to 1275 HV0.025) during subsequent low-temperature (350°C) carburizing. Combined treatment with carburizing at a temperature of 500 °C increases the microhardness of the steel to 820 HV0.025, and the total hardening depth is 500 microns for both combined treatments. It has also been found that plasma carburizing of the steel leads to a decrease in the eddy-current readings compared to the quenched steel and their growth compared to the steel subjected to frictional treatment, which can be used to develop quality control techniques for such treatments.

The evolution of the structure and mechanical properties of medium-carbon microalloyed steel after quenching and tempering at 650оС of various durations has been studied. It is shown that the change in the microstructure and softening of steel with an increase in the duration from 2 to 3000 minutes falls on two stages of martensite tempering: medium (stage II) and high-temperature (stage III). Intensive drop of strength properties ~ 100 MPa/min at stage II is replaced by a very inert softening ~ 0.1 MPa/min at stage III. Using TEM, EBSD and X-ray diffraction analysis the evolution of the microstructure was observed and a quantitative estimation of the strengthening components and their relative contribution to the yield strength at different stages of tempering was performed.

In this work, homogeneous nanostructured and ultrafine-grained (NS and UFG) states with an average grain size of 95 nm and 200 nm, respectively, are formed in the 1565ch alloy of the Al-Mg system. In both states, the microstructure is formed by a network of predominantly high-angle grain boundaries. It has been shown that an alloy with an NS and UFG structure formed at room temperature by high-pressure torsion (HPT) and at 200°C by equal-channel angular pressing according to the Conform scheme (ECAP-С) exhibits similar signs of superplastic (SP) behavior at low temperatures 250 …300 °С in the range of strain rates 5×10-4 s-1…10-2 s-1: elongation values were 170…560%, the rate sensitivity coefficient (m) was 0.3-0.73 at low flow stresses . The temperature range of stability of the strength characteristics of the 1565ch alloy in the NS and UFG states was established, both after thermal and deformation-thermal treatment. It is shown that the material in both studied structural states retains a high level of strength after deformation under SP conditions. The deformation relief formed on the working part of the NS and UFG samples of the 1565ch alloy at the stage of a steady-state SP flow is analyzed.