Physics of Metals and Metallography

Grain boundaries in polycrystalline molybdenum have been studied by emission Mössbauer spectroscopy on 57Co (57Fe) nuclei. It has been shown that Co atoms diffuse along the grain boundaries by the interstitial mechanism. The states of Co atoms in grain boundaries and in near-boundary regions of the crystallites have been analyzed. The values of the effective diffusion coefficient in the subboundary regions of the crystallites have been estimated. The temperature dependence of the grain-boundary segregation factor of Co in Mo has been determined.

Optical properties of spatially ordered nanocomposites consisting of spherical dielectric and metallic nanoparticles have been investigated. On the basis of the method of integral equations, expressions for the field inside and outside the system have been derived and studied. It has been shown that, depending on the material and geometrical parameters of the nanoaggregate, two different states of the system can be obtained, which differ in the presence or absence of a band gap (interference reflection peak) in the visible range for photons with a certain energy. It is shown that at definite parameters of the nanostructure the scattering and absorption of light by nanoparticles diminishes and the ensemble under consideration becomes transparent. The position of the spectral ranges of transparency of metallic composites on the wavelength scale in this case is determined by the frequency of the polariton resonance inherent in the nanoclusters that form the nanocomposite. A heterogeneous material formed of close-packed dielectric nanospheres is suggested, which at some wavelengths possesses a 100% light transmission.

Structural stability of small Ni, Al, and Au metal clusters with a number of atoms close to N = 55 and 147 has been studied by the method of molecular dynamics with the use of realistic potentials of interatomic interaction. It has been shown that in Ni, in which the icosahedral configuration is most stable, the mass spectrum predominantly contains peaks, which correspond to N = 55 and 147. At the same time, for Au and Al clusters, the consequence of magic numbers differs from that specified by the close packing of atoms, and its realization depends on experimental conditions. The results obtained allow concluding that the position of peaks in the mass spectrometric experiments with small clusters is determined by morphological features of the structural state, which depend on the character of interatomic interaction.

A connection has been established between the structural state (phase composition) of the nanocrystalline alloys Fe73.5 − x Co x Cu1Nb3Si13.5B9 (x = 0, 10, 20, 30) and the type of the induced magnetic anisotropy (IMA), which is formed in the process of thermomechanical treatment (TMechT), on the one hand, and its thermal stability, on the other hand. It is shown that the addition of cobalt entails a decrease in the quantity of Fe-Si grains and the formation of phases that contain Fe-Co-B. The induced magnetic anisotropy depends on the volume fractions of structural components, their elastic properties, and coherent bonding of their crystal lattices.

Profilometry and optical and transmission electron microscopy are used to examine the microstructure of surface layers of a low-carbon ferrite-pearlite steel subjected to turning and ultrasonic finishing. It is shown that turning peaks and valleys have different microstructures, which stipulates manifestation of technological hereditary when processing surfaces of machined parts. Ultrasonic finishing causes the severe plastic deformation of the surface layer, which favors the elimination of a technological heredity that is acquired during turning.

Laws of the formation of substructure and of changes in the hardness and in the mechanical properties have been established for sheets of 1545K alloy obtained by tension according to different technologies at various accumulated strains. With an increase in cold deformation (e cold) from 0 to 2.64, the yield stress of cold-worked sheets increases from 355 to 466 МPа and the relative elongation decreases insignificantly from 4 to 3.5%. The maximum strength with σ0.2 = 410 МPа, σu = 460 МPа, and δ = 6.5% is provided by annealing at 150°C for 1 h of the sheets obtained via the technology with the maximum fraction of cold deformation (e cold = 2.64). After annealing at 300°C for 30 min, a twofold increase in the plasticity is observed without a significant reduction in the strength characteristics a follows: σ0.2 = 385 МPа, σu = 436 МPа and δ = 13%. It has been shown that the level of mechanical properties is determined by the substructure that is formed inside deformed grains during annealing.

The evolution of the phase and structural states during heating of a powder mixture of composition Al65Cu23Fe12 subjected to mechanoactivation has been investigated. The solid-state transformations have been studied using Mössbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry. The sequence of phase formation during heating was compared with the data on the heat of formation of binary solutions and compounds in the system. The analysis performed showed that the nature of transformations in the process of the formation of the quasicrystalline phase was caused by the thermodynamic parameters of the system.

The changes in the structure, phase composition, and physicomechanical properties of titanium-free maraging alloys based on the Fe-15–23% Ni-(Co, Mo, V) system after heating to the single-phase α field and two-phase α + γ field have been studied. It has been established that the strengthening of N15K10M5F5-type maraging alloys is caused by the precipitation of fine particles (20–50 nm) of intermetallic phases such as the fcc Ni3(Mo, V) phase and the Fe2(Mo, V) Laves phase (in the N23K9M6 alloys, with the formation of the Ni3Mo and Fe2Mo phases). It has been shown that the two-step aging of the N15K10M5F5 alloy leads to an additional strengthening by 200–250 MPa and provides the achievement of the ultimate tensile strength σu=2400−2500 MPa. The high-strength N15K10M5F5 maraging alloys are obtained with two levels of the coercive force H c: (a) semihard maraging alloys with H c=20−50 Oe and σu=2100−2400 MPa; and (b) hard magnetic maraging alloys with H c=180−230 Oe and σu=1500−1800 MPa. The high-strength titanium-free N15K10M5F5 and N23K9M6 maraging alloys possess many properties characteristic of structural, elastic, and magnetic alloys and are thus multifunctional materials. These alloys can be used for advanced high-tech articles and as high-strength magnetic materials.