Vol 118, No 2 (2017)

The pairwise interaction energies of O–O and N–N in bcc metals of group VB, which were calculated earlier using first-principles methods, have been employed to analyze the effect of the interatomic interactions on the configurational contribution to the thermodynamic activity. The strong effect of interstitial- interstitial interaction has been shown. The configurational contribution grows in the row (Nb–N) → (V–N) → (Ta–N) → (Nb–O) → (V–O) → (Ta–O), which is caused by a weakening of the mutual attraction of interstitial atoms in these solid solutions. The strong repulsion that characterizes the majority of coordination shells only weakly affects the thermodynamic activity. The character of the temperature dependence of the configurational contribution is defined by the strength of the mutual attraction of the interstitial atoms, i.e., upon strong attraction, the contribution increases with increasing temperature (Nb–N, V–N, Ta–N, and Nb–O) and, upon weak attraction, it decreases (V–O and Ta–O).

It has been shown that, in some amorphous alloys, the value of initial bending stresses σ_m can influence the development of the relaxation of these stresses during the annealing of the alloys. These alloys include Co₆₉Fe_3.7Cr_3.8Si_12.5B₁₁, with a nearly zero saturation magnetostriction (λ_s < 10^–7) and the Fe₇₈Ni₁Si₈B₁₃ alloy with λ_s = 25 × 10^–6. In the iron-based Fe₈₁Si₄B₁₃C₂ and Fe₅₇Co₃₁Si_2.9B_9.1 alloys, no effect of the initial bending stresses on their relaxation has been observed. No this effect has also been observed in the metalloid-free alloys Со₈₀Mo₁₀Zr₁₀ and Со₈₀Mo₈Ni₂Zr₁₀ with a nearly zero saturation magnetostriction λ_s. When this effect manifests itself, the activation energy U of the given process becomes a function of two factors; i.e., this energy depends on both the composition of the alloy (that is, interatomic forces) and the value of the initial bending stresses. In this case, the activation energy U cannot be considered to be characteristic of the material.

Results of investigations of structural and magnetic properties of Fe/Cr/Gd superlattices that differ in the thicknesses of the Cr interlayer have been reported. The insertion of the Cr interlayer between Gd and Fe layers has been found to lead to structural changes in Gd layers and the appearance of an additional fcc phase in them along with the main hcp phase. The new fcc phase is uniformly distributed across the thickness of the layer and is not localized near layer boundaries or in the center of Gd layers. Polarized-neutron reflectometry was used to show that the aforementioned structural changes are accompanied by a substantial (two-fold to threefold) decrease in the average magnetization of gadolinium over a wide temperature range. Near interfaces of the Gd layer, a layer appears that is two-to-three monatomic layers thick and characterized by increased magnetic moment.

The effect of accelerated Ar⁺ ions on the crystallization process and magnetic properties of nanocrystalline Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy has been studied using X-ray diffraction analysis, transmission electron microscopy, thermomagnetic analysis, and other magnetic methods. Irradiation by Ar⁺ ions with an energy of 30 keV and a fluence of 3.75 × 10¹⁵ cm^–2 at short-term heating to a temperature of 620 K (which is 150 K below the thermal threshold of crystallization) leads to the complete crystallization of amorphous alloy, which is accompanied by the precipitation of the α-Fe(Si) solid solution crystals (close in composition to Fe₈₀Si₂₀), Fe₃Si stable phase, and metastable hexagonal phases. The crystallization caused by irradiation leads to an increase in the grain size and changes the morphology of grain boundaries and volume fraction of crystalline phases, which is accompanied by changes in the magnetic properties.

Nickel nanotubes have been formed in pores of ion-track membranes using electrochemical deposition. Morphologic and structural features of these nanostructures have been comprehensively studied. The evolution of the nanotubes wall thickness and parameters of their crystalline structure by variations of the synthesis voltage and temperature has been determined. On the base of these data the nanotubes growth mechanism has been estimated.

The effect of stabilizing crystal size in a melt-quenched amorphous Fe₅₀Ni₃₃B₁₇ ribbon is described upon crystallization in a temperature range of 360–400°С. The shape, size, volume fraction, and volume density have been investigated by transmission electron microscopy and X-ray diffraction methods. The formation of an amorphous layer of the Fe₅₀Ni₂₉B₂₁ compound was found by means of atomic-probe tomography at the boundary of the crystallite–amorphous phase. The stabilization of crystal sizes during annealing is due to the formation of a barrier amorphous layer that has a crystallization temperature that exceeds the crystallization temperature of the matrix amorphous alloy.

Tri-layered α-brass-clad Cu–Cr-alloy composite plates were prepared by hot roll-bonding. Neither intermetallic-compound layers nor interface defects were observed at the interfaces in the as-rolled and heat-treated α-brass-clad Cu–Cr composite plates. The hardness of the as-rolled α-brass layer was greater than that of the Cu–Cr substrate, since the α-brass was strengthened by strain hardening more efficiently upon rolling. The hardness of the α-brass decreased appreciably upon annealing because of the recovery processes, whereas that of the Cu–Cr layer slightly increased after heat treatment at 450°C due to the precipitation strengthening. After the post-roll-bonding heat treatment at 450°C, the strength of the α-brass-clad Cu–Cr-alloy composite decreased with a significant increase in ductility. The electrical conductivity of the asroll-bonded α-brass clad Cu–Cr alloy composite (47–52% IACS) increased significantly (to 72–74% IACS) after the 1-h heat treatment. The strength and conductivity of the clad composite are dependent on the precipitation strengthening of Cu–Cr and recovery softening of α-brass in the course of the post-roll-bonding heat treatment.