Vol 120, No 5 (2019)

In the dynamic theory of martensitic transformations the wave mechanism of growth of martensite crystals is controlled by the overlap of wave beams of quasi-longitudinal (or longitudinal) waves that carry deformation of the “tension–compression” type in orthogonal directions. The appearance of wave beams is considered a consequence of the appearance of the initial excited (vibrational) states. The presence of the transformation twins is interpreted as the result of the matched propagation of relatively long-wave (???? waves) and short-wave (s waves) displacements. With the aid of the Fourier transforms, an analysis was performed of the influence of the diffraction divergence of a pair of orthogonal wave beams on the formation of a region of their superposition, including the limiting case of narrow beams with one of the transverse dimensions of the front less than λ/2, where λ is the wavelength. The connection of the distribution of the amplitudes of spatial harmonics with the configuration of the initial excited state is discussed.

Spin dynamics of the LaMn₂O₅ compound, which contains manganese ions with different charges in two crystallographically different positions, has been investigated. The description of the dynamics is based on the equations of motion for the irreducible spin operators. It has been shown that the presence of a noncollinear antiferromagnetic ordering of manganese ions in the different crystallographic positions leads to the necessity of not only the determination of the frequencies of spin excitations, but also the formulation of conditions for the stability of the magnetic state relative to which the dynamic processes are considered.

Al/Mg–Li/Al composite plates were fabricated by hot rolling with 50% thickness reduction at 673 K and annealed at 473–673 K for 1 h. The microstructure and mechanical properties of the composite plates under different annealing temperatures were investigated. The results show that the composite plates with a good bonding interface are fabricated. The diffusion layer consisting of Al₃Mg₂, Al₁₂Mg₁₇, AlLi, and MgLiAl₂ has formed at the interface after annealing at and above 623 K, while the interfacial bonding strength increases with the annealing temperature. The microhardness of the interface increases rapidly when the annealing temperature is above 573 K. The elongation of the composite plate increases with annealing temperature. The tensile strength decreases when annealing temperature is above 573 K.

This work investigates the influence of structural state of the initial powders of composite material Inconel 625/TiC on the tendency to crack formation in the process of direct laser-assisted growth. It has been shown that the preliminary mixing of powders in a planetary ball mill, in contrast to their separate supply or mixing of powders in a gravitational mixer, makes it possible to avoid the formation of cracks in the synthesized object. It has been established that in the process of mixing of powders in a ball mill, a layer of titanium carbide is formed on the surface of the Inconel particles, and the carbide phase is subjected to mechanoalloying by the elements of the matrix. The change in the structural state of the powder leads to a change in its thermophysical properties, which has an effect on the crystallization processes. At the laser power P = 400–800 W, the carbide phase is not melted in the composite materials obtained from powders mixed using a ball mill, whereas when using a separate powder supply and upon their mixing in the gravitational mixer, the TiC phase undergoes recrystallization.

Cast composite material based on Cr₂AlC MAX phase has been prepared by metallothermic self-propagating high-temperature synthesis (SHS) from a mixture of powders of chromium oxide, aluminum, and carbon. The experiments have been performed using an SHS reactor with a volume V of 3 L under an excess inert gas (Ar) pressure (P = 5 MPa). The prepared material has been studied by X-ray diffraction analysis, scanning electron microscopy, and local microstructural analysis. The quantitative analysis has been performed by the Rietveld method. The electrical resistivity was measured in the 100–1300 K temperature range. The resulting material is an electrical conductor with metallic conductivity in the 100–1300 K temperature range, and has the electrical resistivity of the same order as the samples containing 100% Cr₂AlC.

To study the mechanical properties and elastic behaviour of Q&P steel, which is a type of advanced high strength steel, uniaxial tension and cyclic loading tests have been conducted. Scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) tests have been conducted on deformed samples with different degrees of deformation to analyse the microscopic mechanisms of their change in elastic modulus. The results have been shown a significant growth in the elastic modulus of alloyed steel after the initial unloading, followed by a decrease in the elastic modulus with the increase in the degree of unloading. The unloading and reloading paths showed a clear nonlinearity and formed a closed loop. The unloading chord modulus also decreased gradually with the increase in a pre-strain. The results of SEM, TEM, and XRD have been shown that the phase transformation variation is the strongest during the early stage of plastic deformation, and then gradually decreases. Cyclic loading has promoted the transformation from austenite to martensite. Interactions of the residual stress, phase transformation, and dislocation movement affecting the change in elastic modulus are determined through this research.

Abstarct

—The effect of the annealing temperature on the texture state and level of damage D of sheets of the steel DP600 (0.10% С, 0.15% Si, 1.4% Mn, 0.007% Р, 0.008% S, 0,009% N, 0.02–0.06% Al, 1% Cr–Mo–Ni) with a ferritic–martensitic structure and a texture of recrystallization and cold rolling has been studied in this work. The level of D was estimated based on the results of measurements of the Young’s modulus E and direct electron-microscopic observations. An increase in E after annealings in the 220–275°С temperature range stops; yield plateaus appear in the tensile curves, the yield stress increases, and the yield strength decreases in all directions of measurements. A redistribution of orientations can be seen in the texture, which does not affect the magnitude of E. These annealings are associated with the least level of D of the steel sheets, which after prolonged annealings can be considered to be “conditionally undamaged.” Further annealings (to 400°С) change the texture state of the sheets (three texture characteristics are increased) and the values of E in different directions and increase the level of damage. The values of D show up an anisotropy similar to that characteristic of E.