Materials Science最新文献

The influence of polyvinylpyrrolidone (PVP) with molecular mass of 12 600 and 28 000 at concentrations of 0.2; 0.5 and 1.0 g/dm³ on the corrosion rate of 20 steel in the chloride-acetate solution and in the model stratal water was investigated by gravimetric and electrochemical methods. Under dynamic conditions maximum inhibition of the steel corrosion rate was observed at a PVP concentration of 0.5 g/dm³ in both environments. A further increase in inhibitor concentration to 1.0 g/dm³ reduces the degree of protection more significantly in chloride-acetate solution than in the stratal water. The PVP with a higher molecular mass reveals higher protective properties, which is typical of polymers capable of adsorbing both linearly and in a ball.

The influence of the modes of anhydrous nitriding of 08Kh18N10 steel on its phase composition, distribution of the main alloying elements, and the content of nitrogen in the nitride layer, microhardness and specific wear were investigated. With an increase in the temperature and duration of 08Kh18N10 steel nitriding simultaneously with the increase in the thickness of the nitrided layer, the nitrogen content in steel decreases and a drop in the hardness of the upper part of the nitride zone was observed. At the same time, the hardness gradually increases to the maximum values typical of the boundary of the nitride and diffusion zones. Laboratory tests on hydroabrasive wear showed that, compared to the initial state, the wear resistance of 08Kh18N10 steel, nitrided at P = 120 Pa, T = 600°C for 3 h, increased twofold. Industrial tests of centrifuge rotors at concentrating mills confirmed the results of laboratory investigations.

Welding processes of titanium alloys with steels are analyzed. The following research directions are distinguished: the use of prefabricated bimetallic transition elements (welded by traditional methods); minimization of energy and heat expenditure in the weld area of metals; the use of methods of welding metallurgical engineering. The advances in welding technology have led to innovative solutions such as friction welding with stirring, as well as the use of liquid-phase layers and 3D printing of nanostructured layers at the edges to accelerate diffusion processes in diffusion welding. The new methods in welding metallurgical engineering increase the efficiency of Ti–Fe compounds due to the use of multilayer compositions of tantalum or niobium from the side of titanium and bronze – from the side of steel, and also vanadium inserts and its alloys, for example, alloyed with tungsten or chromium. The urgency of further development of standards for support and dissemination of industrial technologies for welding of Ti–Fe joints, training and preparation of technical personnel for the implementation of these technologies is noted.

The results of a set of experimental tests of Q420 steel samples with quality level Q420B are presented. The chemical composition of steel and its mechanical characteristics, indicated in the certificate for products and determined experimentally, were compared with the standard values in the certificate for products. The results of steel fatigue and corrosion-fatigue tests were analyzed. The S–N curves in air and artificial seawater were constructed, and the corresponding values of endurance limits at room temperature and at 0°C were also determined. A significant influence of the corrosive environment on fatigue crack propagation rate in steel was established.

The effect of impact-oscillation loading of a given intensity on the hardness of the surface layers of the D16ChATW aluminum alloy was evaluated, in particular, using nanosolutions of tungsten carbide, carbon, as well as Al + Cu and Al + Cu + Mg nanosolutions at a concentration of 50:50% and 33:33:33%, respectively. The relationship between the parameters of dynamic non-equilibrium processes which change the structural phase state and mechanical properties of the alloy and the surface hardness of the material, was identified and described.

The effect of the electrolyte composition for hard anodizing of aluminum on the corrosion resistance of the synthesized anodic coatings was studied. The hard anodizing was carried out at temperatures of –4–0°C for 60 min at a current density of 5 A/ dm² . The basic electrolyte was a 20% aqueous solution of H₂SO₄ . Hydrogen peroxide (H₂O₂) was added to the electrolyte in concentrations of 30; 50; 70 and 100 g/L to determine strong oxidants influence on the characteristics of the anode layers. The concentration of 70 g/L H₂O₂ in the electrolyte, which ensures the synthesis of the thickest and least porous coating, was optimal. At the initial moment of immersion of anodic coatings synthesized in hydrogen peroxide electrolyte, their corrosion resistance decreases. When peroxide electrolyte concentration increases from 30 to 100 g/L, corrosion currents increase by 30 and 90%, respectively. However, with increasing exposure of coatings in the environment, their corrosion current density decreases more intensively with a decrease in their porosity. After 14 days, no dependence of the coatings corrosion durability on the composition of the electrolyte observed, what indicated a complete closure of the pores.

Differences in the oxidation kinetics of zirconium and Zr–1% Nb alloy during heating in air depending on the heating rate, temperature and exposure time are revealed. The increase in the heating rate from 2.5 to 6 and 7.5°C/min reduces the activation energy of the Zr oxidation process in the temperature range of 20–1000°C from 70.2 to 67 and 52.7 kJ/mol, respectively. For the Zr–1% Nb zirconium alloy, increase in the heating rate from 5 to 10 and 20°C/min causes an increase in the activation energy of the oxidation process from 65 to 70.1 and 78.5 kJ/mol, respectively. Such an increase in the heating rate (of zirconium from 2.5 to 7.5°C/min, and of the Zr–1% Nb alloy from 5 to 20°C/min) causes a decrease in the thickness of the ZrO₂ oxide film. During isothermal exposure for 5 h at 750°C, Zr–1% Nb alloy and Zr at a temperature of 800°C are oxidized according to the parabolic law. At 800°C Zr–1% Nb alloy oxidizes according to the combined law: first, parabolic, and then quasi-linear.

The structure and mechanical properties of 4Kh4N5M4F2 steel in thermodeformed and cast states after quenching and tempering, and additional heating are investigated. After additional heating of hardened and tempered 4Kh4N5M4F2 steel, which models the operating conditions of the equipment (operating temperature during quasi-stationary exposure), at 630–650°C steel softens, which is associated with the formation of Me₇C₃ carbides. Such carbide phase in the metal structure of the cast steel under mentioned conditions is absent and is accompanied by the increase in its heat resistance. The expansion of the operating temperature range of cast 4Kh4N5M4F2 steel after the optimal mode of hardening and tempering allows using a tool made of this steel up to the operating temperature of 650°C. It is recommended not to use such steel in the cast and thermodeformed states for the manufacture of tools for hot deformation of non-ferrous metals and alloys, which operate under cyclic impact loading.

The influence of electron concentration, mixing enthalpy, and dimensional mismatch on the lattice parameter, elastic modulus, and normalized hardness of fcc high-entropy alloys (HEA) is studied. The lattice parameter, which determines the elastic modulus of HEA, is influenced by both the electron concentration and the mixing enthalpy. A rectilinear dependence of the normalized hardness of these alloys on the dimensional discrepancy is established. Formulas for calculating the hardness and the elastic modulus for hard-soluble HEA with fcc lattice are proposed.

The effect of different concentrations of CO₂ and H₂S in a chloride-acetate solution on corrosion-mechanical properties of 17G1S-U steel was studied. In a solution saturated with CO₂, the corrosion rate of steel was lower than in the presence of H₂S, but increased over time due to the absence of protective carbonate films on the surface, plasticity parameters were 2–2.7 times lower than in air due to dimple surface damage. The corrosion rate and hydrogenation of steel was determined primarily by the hydrogen sulfide concentration in the environment. At a concentration of 100 mg/dm³, dense films of the troilite-mackinavite composition were formed, which inhibit corrosion. At higher concentrations, the corrosion rate increased due to the sulfides transformation and the formation of surface layers with defects. With an increase in the H₂S concentration from 100 mg/dm³, the strength characteristics of steel decreased in three times, and plasticity decreased in 3–5 times.