Vol 125, No 10 (2024)

The impact of elastic energy anisotropy on the drag thermopower in noble metals at low temperatures has been investigated. In order to describe the interaction of electrons with longitudinal phonons, the strain potential theory has been employed. In calculating electron relaxation on shear components of vibrational modes, the electron–phonon interaction constant, previously determined from a comparison of the calculated electrical resistivity of Au, Ag, and Cu bulk crystals with experimental data, was used. The maximum values of the drag thermopower in perfect noble metal crystals have been determined. These values are independent of the electron–phonon interaction constants; rather, they are determined by the elastic moduli of the second order, crystal density, and electron concentration. It has been demonstrated that quasi-transverse phonons constitute predominant contribution to the drag thermopower at low temperatures, whereas the contribution of longitudinal phonons were found to be negligible. At the same time, for perfect Au, Ag, and Cu crystals, the dominant contribution to the electron–phonon drag is provided by the slow t2-mode.

X-ray and magnetometry methods are used to show that, during magnetron sputtering of Dy/Co periodic multilayer systems, the DyCo₂ and DyCo₃ intermetallics form. The main reason for the phase formation of various intermetallics is the structural state of buffer layer, namely, its crystalline and amorphous state in the case of crystalline and glass substrate, respectively.

The distribution of magnetic permeability over the cross section of rapidly quenched amorphous Co_68.6Fe_3.9Mo_3.0Si_12.0B_12.5 ribbons was studied in the range of elastic tensile stresses from 0 to 480 MPa. This distribution was restored using magnetic impedance tomography, which is a method based on the analysis of the frequency dependences of the impedance, when external magnetic fields of varying amplitude or tensile mechanical stresses are applied to ribbons. In this case, the alternating-current frequency varied in the range from 0.01 to 80 MHz.

Molecular dynamics (MD) simulations are applied to study primary damage formation in a Fe–10 at.% Cr binary model alloy. 14 784 events of radiation defect formation are initiated by either Fe or Cr primary knocked-out atoms (PKAs) with PKA energies 100 eV ≤ E_PKA≤ 5 keV introduced along twenty-two nonequivalent crystallographic directions. The generated sample is used to calculate the average threshold displacement energies. It is shown that in the considered material the average threshold displacement energy of Fe and Cr atoms is the same and equals ⟨E_d⟩= 24.5 ± 0.6 eV. It is also established that the dependence of E_d on E_PKA splits into two linear fragments determined by the governing defect formation mechanism. The formation of isolated point defects at low PKA energies E_PKA≤E_cc, where E_cc≈ 0.84 keV, is replaced by defect formation in collision cascades initiated by PKAs with energy E_PKA≥E_cc. Using MD simulation results, we modified the cascade function in the Kinchin–Pease model to take into account the dependence of the threshold displacement energy on the PKA energy.

The evolution of the structure of chromium–hafnium bronze under high-speed severe plastic deformation by dynamic channel-angular pressing (DCAP) and subsequent annealing has been studied. It is shown that fragmentation of the structure under DCAP occurs predominantly through the twinning mechanism, especially upon two passes. In this case, significant strengthening occurs and the microhardness increases to 1750 MPa. When bronze is annealed, additional strengthening occurs due to the precipitation of Cu₅Hf and Cr particles. The structure of bronze after DCAP has high thermal stability, and maximum hardness is achieved after annealing at 400°C. The strengthening and thermal stability of the structure in chromium–hafnium bronze is higher than in hafnium bronze.

The morphological and crystallographic features of two-phase α+β-states in the Zr–2.5Nb alloy formed during cooling from the β-region at different cooling rates (“water”, “air”, “furnace”) were studied using X-ray diffraction analysis and scanning electron microscopy, including orientation analysis using electron backscatter diffraction. In addition to orientation maps (EBSD), the crystallographic analysis used spectra of misorientations of intercrystallite and interphase boundaries, as well as the restoration of high-temperature β-grains using Burgers orientation relationships. It is shown that with significant differences in the morphological features of the structural states caused by the cooling rates, almost the same picture is observed crystallographically: complete coincidence of the spectra of misorientations of intercrystallite (α'/α' and α/α) and interphase (α'/β and α/β) boundaries. X-ray analysis did not record the presence of the β-phase in the alloy structure upon quenching in water, but showed its noticeable amount at lower cooling rates. In this case, the chemical composition of the β-phase is close to the point of invariant transformation (~ 20 at. % Nb). An assumption is made that at all cooling rates, phase transformations are realized by the same mechanism - shear rearrangement of the bcc ↔ hcp lattice, accompanied by directed jumps of individual atoms. It has been confirmed that the observed β-phase is not retained from the high-temperature region, but is released during phase transformations by the shift-shuffling mechanism at previously formed α'/α'- or α/α-boundaries.

The paper investigates the evolution of the structure and properties of low-alloy dispersion-hardening alloys based on Cu–Zr, Cu–Cr, and Cu–Cr–Zr systems under high-speed deformation (~10⁵ s^-1) by dynamic channel angular pressing (DCAP) and subsequent annealing (aging) at 200–700°C. The effect of alloying with microadditives Cr (0.09–0.22%) and Zr (0.04–0.20%) in achieving high hardness of copper with a submicrocrystalline structure obtained by DCAP was studied. The effect of ECAP and subsequent aging on the electrical conductivity of alloys is studied. The sequence of decomposition processes of a copper–based α-solid solution with the precipitation of nanoscale particles of the second phases and recrystallization is determined. It is shown that the role of zirconium is due to the precipitation of Cu₅Zr phase nanoparticles during DCAP and subsequent annealing on dislocations and sub-boundaries, their fixation, and reduced mobility, as a result, the process of formation of recrystallization centers slows down, which requires rearrangment (restructuring) of the dislocation structure.