Vol 2019, No 10 (2019)

Abstract—The migration energies of a vacancy and an interstitial atom in the ordered CuPt alloy are calculated using molecular dynamics simulation. A high interstitial atom migration anisotropy is detected: as a rule, an interstitial atom migrates along the (111) planes containing copper atoms. A similar anisotropy is also observed for the vacancy migration during elastic tensions along these planes.

Abstract—The stratification effect (concentration heterogeneity) in melt-spun Fe–B alloy ribbons is discussed. The influence of the solidification rate and alloying elements (Cr, Sn, Mo) on the concentration heterogeneity across the ribbon thickness is studied. The type and character of ordering of the alloys on an atomic level are analyzed. The existence of Cr and Mo in the alloys is found to favor a more homogeneous distribution of the Fe–B matrix elements across the ribbon thickness.

Abstract—An approach, which is based on modified phenomenological models of the rheological behavior of metallic materials under superplasticity conditions, is proposed to describe the grain size distribution during superplastic flow with allowance for grain refinement. The characteristic features of experimental grain size distributions are shown to be successfully simulated.

Abstract—To determine a crack growth direction, we propose to take into account constant T-stresses and the higher-order terms in the expansion of the stress field at a crack tip by representing them as a function of the angular distribution of T-stresses. A modified criterion is suggested for determining a crack growth direction using the maximum tangential stresses with allowance for the angular distribution of T-stresses at a crack tip.

Abstract—The hardness and the tribological properties of the AK10M2N silumin subjected to irradiation by a high-energy pulsed electron beam with an energy density of 35 J/cm² are studied. As compared to the as-cast state, the microhardness of the surface layers increases by ≈20% (up to ≈1.2 GPa), the friction coefficient decreases by a factor of ≈1.3 (down to 0.42), and the wear parameter decreases by a factor of ≈6.6 (down to 0.74 × 10^–3 mm³/(N m)). These changes are shown to be caused by the dissociation of silicon and intermetallic compounds in the surface layer during irradiation by a high-energy pulsed electron beam.

Abstract—Deformation-induced composites consisting of alternating layers of amorphous Fe–Ni–B and Co–Fe–Cr–Si–B alloys are prepared by consolidation via high-pressure torsion in a Bridgman chamber. The sequence of changing structural states of the composites and their individual components upon severe plastic deformation and variations of the Vickers hardness and magnetic characteristics are studied in accordance with the degree of deformation. It is found that the use of high-pressure torsion at a high strain efficiently favors the transition of the materials from an amorphous into a nanocrystalline state, increases their microhardness, and retains soft magnetic properties.

Abstract—The influence of the graphene content (up to 2 wt %) and the sintering conditions on the temperature dependence of the electrical resistance of an Al₂O₃/graphene composite material in the temperature range 20–1600°C is studied. The composite material is fabricated from a mixture of initial powders by spark plasma sintering and hot pressing. The electrical resistance of the compacted material is found to depend on the pressing force and a heating method. The composite material prepared by hot pressing has the minimum electrical resistivity (0.9 Ω m).

Abstract—The structure and the mechanical properties of Nb₈₀C₂₀ and Nb₄₀Mo₄₀C₂₀ alloys have been studied at temperatures 20–1500°C. The mechanical properties of the Nb₈₀C₂₀ alloy from room temperature to 1300°C are shown to be slightly lower than those of complex Nb–Si alloys. The short-time and 100-h strengths of the Nb₄₀Mo₄₀C₂₀ alloy at 1500°C are higher than those of Nb–Si alloys. The Nb₄₀Mo₄₀C₂₀ alloys have a low fracture toughness.

Abstract—The structure and the ultimate tensile strength of the bimetallic joints of a TsM2A (Mo–Ti–Zr system) molybdenum alloy and a corrosion-resistant 12Kh18N10T steel are studied. These joints are formed by diffusion welding under hot isostatic pressing conditions using the following combined intermediate layers: vanadium–electrical sheet steel, vanadium–copper, and titanium–niobium–copper. The highest strength of the joint (419 MPa) is reached when a combination intermediate layer of titanium, niobium, and copper is used.

Abstract—Optical and atomic force microscopy is used to study the structures of pearlitic and ferritic steels. The advantages of atomic force microscopy for studying the steel structures are shown in comparison with traditionally used optical techniques.

Abstract—The influence of argon-arc welding and laser welding on the fatigue properties and the fracture of a foam–aluminum sandwich is studied. Argon-arc-welded samples are found to have the highest fatigue strength.

Abstract—The development of structural damage and cracking in a landing head used in Western Siberia is studied. The landing head is made of 20KhNL steel, which is an analog of T32MoCN8R steel produced in Romania. Crack growth is detected on the outer side of the landing head at the site of intersection of its end face with the ring surface. The experimental results obtained in this work demonstrate that the following two types of structural changes, which involve diffusion-mobile hydrogen, take place in the landing head during operation: the formation of a long chain of pores along the boundaries of the former austenite grains and the formation of ferrite bands, in which cementite particles dissolved.

Abstract—The results of studying the mechanical behavior of a 23Kh15N5AM3-Sh (VNS9-Sh) sheet TRIP steel with various initial martensite contents during static tension are supplemented and generalized. A correlation between the type of stress–strain curve and the acoustic emission (AE) signal activity and power, on the one hand, and the change in the strain-induced martensite content in the surface layers of the TRIP steel during static tension, on the other, is found and analyzed. The TRIP steel in an austenitic–martensitic state with approximately the same phase contents is found to have the optimum mechanical properties.

Abstract—The stiffness and damping properties of various-thickness samples made of a composite material based on a rubber mixture, rubber fiber composite material, and thermoplastic elastomers of various stiffnesses are studied under static and dynamic loading conditions at a temperature of 23 and –40°C. The composites based on a rubber mixture and the rubber fiber composites are recommended for the dampers that work in regions with low climatic temperatures. The stiffness and damping properties of a real object are assumed to be estimated using the elastic hysteretic properties of a test sample.