Materials Science最新文献

The inoculation of nano-sized particles of refractory Al₂O₃, TiO₂, MgO, ZrO₂ oxides into the welding bath was studied. The inoculation of oxides with a low-level mismatch to the δ-Fe lattice and increased wetting with liquid iron ( MgO, ZrO₂) contributes to the growth of dendrites, which are formed during melt crystallization. Metal modification with MgO, ZrO₂ oxides decreases the hardness of polygonal ferrite and increases the content of lower bainite in the microstructure of joints, brittle fracture resistance of the joint metal. Metal modification with Al₂O₃, TiO₂ oxides contributes to an increase in the hardness of polygonal ferrite, the content of upper bainite in the joint microstructure, and the strength of welded joints of low-alloy steels.

The stress state of a soft interlayer under contact strengthening, when tensile stresses are greater than the yield strength of the interlayer metal and less than the stresses causing a general yield, is considered. The analytical expressions under plain strain and axisymmetric tension are obtained. In the first case, the stresses are determined using the Airy stress function as a corresponding polynomial, in the second case – based on the stress function of the fifth degree, built on the corresponding Legendre polynomial. The stresses satisfy the differential equations of equilibrium and boundary conditions.

Methods of modeling silicon carbide particles of asymmetric shape as well as the methods of image analysis of the surface layer of the aluminum alloy reinforced with silicon carbide particles were developed. A 3D modeling of the distribution of silicon carbide particles of different sizes and filling percentages in the surface layer of the aluminum alloy was carried out. The distribution of silicon carbide areas in different cross-section planes and with different volumetric filling of the strengthened layer was established.

High-entropy alloys (HEA) based on the renewal of elements of the V–IX groups of the Periodic Table, which are capable of forming σ-phase with each other, are studied. The formation of the σ-phase in the range of electronic concentration of 6.7-8 el/at was monitored. The effect of electron concentration on the content of the σ-phase in HEA-containing elements forming the σ-phase in a two-component system is shown. The conditions for the formation of a single-phase structure of the σ-phase during crystallization of multicomponent HEA are determined. The limits of the existence of a 100% high-entropy phase are established and the influence of lattice parameters on their properties is revealed. A decrease in the size of the parameters c and an of the σ-phase leads to an increase in both the hardness and modulus of elasticity of alloys with a single-phase structure of the high-entropy σ-phase.

Fracture due to hydrogen embrittlement is a major concern for the reliability and safety of hydrogen transportation via gas pipelines. Pipe steels are characterized by high plasticity, therefore, methods of nonlinear fracture mechanics, including the J-integral method, are preferred for determining the fracture toughness. The influence of preliminary electrochemical hydrogen charging under a moderate mode on fracture toughness of API 5L X67 steel in the as-delivered and 34-year operated on the gas main pipeline conditions was studied. A methodological feature of the experiments is the use of different rates of mechanical loading of specimens with cracks. The influence of the long-term operation of steel on its resistance to brittle fracture is revealed, depending on the test conditions.

A methodology for determining the technical state of reinforced concrete bridge structures was developed. It is based on establishing the depth and location of the largest deflection using a laser projection system, as well as an approach to finding the stress-strain state (SSS) along the height of the beam. An energy approach, which foresees the energy of elastic-plastic deformation calculation of concrete and reinforcement was used for this. The specific fracture energy as an invariant characteristic of concrete strength under tension, compression, and also tension of reinforcement were established experimentally. The true diagrams of deformation and fracture of concrete samples taken from the structure were plotted. The results of experimental studies of SSS during the bending of a reinforced concrete beam agree well with those calculated by the finite element method.

The mechanical properties of 15KhSND steel of the beam of the bridge structure were analyzed. The characteristics of strength, plasticity, and resistance to brittle fracture of the steel of its wall correspond to the regulated values. The values of strength and plasticity of the steel shelf do not exceed the normalized limits, but the low values of its impact strength and brittle cleavages on the sample microfractures indicate a tendency to brittle fracture. The resistance to brittle fracture of the metal from the beam shelf decreased in three times on the longitudinal samples, and two times on the transverse ones as compared to the inherent brittle fracture resistance of steel from the beam wall.

Ag(Pd) bimetallic nanostructures (Ag(Pd)NPs) were synthesized using the galvanic replacement of palladium ions with silver nanoparticles. Based on a comparative analysis of the results of scanning electron microscopy, energy dispersive X-ray microanalysis, and X-ray powder diffraction, it was established that the obtained Ag(Pd)NPs can be considered as “core-shell” nanosystems, in which the core is silver, and the shells are palladium nanoparticles with a size of 5–15 nm. Ag(Pd)NPs were studied as catalysts for the aerobic liquid-phase oxidation of benzyl alcohol. The addition of Ag(Pd)NPs to the reaction system accelerates the reaction in 14 times.

The effect of the zeolite-phosphate anti-corrosion pigment obtained by the mechanochemical method on the protective properties of the epoxy coating on carbon steel was investigated. Methods of electrochemical impedance spectroscopy, optical 3D profilometry, and tests in a heat and humidity chamber established that adding such a pigment to an epoxy primer significantly reduces the rate of the metal under-film corrosion.

The resistance of AISI 304 and 08Kh18N10 steels to crevice corrosion in chloride-containing media was studied using potential-dynamic methods. The preset gap width of 0.3 mm between the sample and the counter body simulates the gap between adjacent plates of plate-like heat exchangers. The area of the hysteresis loop of the constructed anode potential-dynamic curves of the forward and reverse stroke was used to compare the volume of local damage caused by crevice corrosion of the studied steels. The maximum areas of the steel hysteresis loop and the volume of local corrosion damage in the ingots with the lowest (2.23×10^–8 and 2.24×10^–8 m³/kg) and highest (2.31×10^–8 m³/kg) values of the specific paramagnetic susceptibility χ₀ of austenite were established. The free corrosion potential E_corr of steels intensively shifts in the negative direction (from –0.28 up to –0.41), and the repassivation E_rp and crevice corrosion E_crev – in the positive direction from –0.38 up to –0.29 and from –0.1 to 0.1 V, respectively, with an increase in the parameter χ₀ from 2.23×10^–8 up to 2.25×10^–8 m³/kg, which contributes to an increase in their ∆E-criterion from 0.02 up to 0.69 V and resistance to crevice corrosion. This is because, in this range of values, the change in the χ₀ parameter is determined by deviations in the content of C, N, S, P, and Cr in the solid solution of austenite in steels. With an increase in the parameter χ₀ of steels to 2.31×10^–8 m³/kg, their potential E_corr shifts in the positive direction from –0.41 up to –0.32, and E_rp , E_crev – in the negative direction from 0.29 up to 0.15 and from 0.10 up to –0.02 V, respectively, which contributes to a decrease in the ∆E criterion of steels from 0.65 up to 0.14 V and their resistance to crevice corrosion. The χ₀ parameter of steels is an integral characteristic of the paramagnetic state of austenite and can be used to assess their resistance to crevice corrosion in chloride-containing media.