Materials Science最新文献

The influence of alloying on the mechanical and corrosion properties of casting eutectic (α-Al + Mg₂Ge) aluminum alloys based on the Al–Mg–Ge ternary system was studied. Corrosion dissolution of aluminum alloys in a 3% NaCl solution was studied by electrochemical (voltammetric, chronopotentiometric) and gravimetric methods. It was shown that according to the scale of corrosion resistance these alloys are stable or very stable, and by the combination of corrosion and strength properties can compete with industrial casting aluminum alloys.

The results of autoclave tests of corrosion resistance of dysprosium titanate powders and pellets in the model environment and the parameters of the primary coolant of the WWER-1000 reactor are presented. During exposure in autoclave for up to 500 h, powders are characterized by the decrease in weight, which does not exceed 0.5%, and weight increase depends on powder density. Pellets with the highest density (7.1–7.2 g/cm³) are most corrosion resistant and with the density of 5.74–5.79 g/cm³ powders corrode with the monotonous weight growth under increasing exposure in the autoclave. After 2300 h of autoclaving, the average increase was approx. 156 mg/dm² (0.3%). The change in the powders and pellets phase composition of dysprosium titanate after corrosion tests was not detected. Studies of the conditions of defective models of absorbing elements after autoclave tests retain their integrity without changing the linear dimensions. After cutting the absorber elements models, the powders were freely removed from the cladding. The change in the powders’ phase composition also was not revealed.

Testing of the reagent method of water treatment with the use of corrosion control devices was performed at the district boiler house of Kyiv city. Corrosion rate probes were installed on the straight and return pipelines of the heating network, and on the feed line. The anti-scale efficiency of the reagent was determined by measuring the change in the hardness of water before and after the heating equipment. Corrosion monitoring showed that the corrosion rate in the heating network is maintained at 0.1 mm/year. The corrosion rate on the feed line due to reagent water treatment was reduced to 0.03 mm/year in non-deaerated water. The calculation of economic efficiency has shown that the reagent method of water treatment for heating networks is by 13% cheaper than traditional approach and can serve as an alternative to the traditional one, especially regarding energy conservation.

The heat-resistant Ti–Al–Zr–Si alloys (base Ti–(6–7)Al–(2–3) Zr–(1–1.5)Si and additionally alloyed Ti–(6–7)Al–(3–5)Zr–(1–1.5)Si–(2–4)Sn), obtained by electron beam smelting were studied. Deformation was carried out in the β- or upper part of the (α+β)-area by means of forging and rolling into a strip. The base alloy was subjected to rolling in the upper part of the α+β-area, and the fine-grained uniform structure with a grain size of 10–20 μm was obtained. Internal stresses and defective substructure of the deformed alloy intensify the decomposition of the solid solution and promote the formation of evenly distributed dispersed silicides, which allows obtaining high strength and heat resistance characteristics. Tensile tests at 20; 650 and 700°C of the Ti–(6–7)Al–(2–3)Zr–(1–1.5)Si alloy samples after deformation and annealing also showed a rather high level of the tensile strength and yield strength. After 20 h exposure at the operating temperature of 700°C, the structure becomes more equilibrium, due to which the strength of the deformed alloy decreases, and the relative elongation increases. Additional alloying of the base alloy with zirconium and tin slightly increases plasticity and decreases heat-resistant properties.

The quality characteristics of the finishing treatment of deposited materials with cutters made of hard alloy and super hard material (hexanite-R) were investigated. During finishing treatment of the deposited parts, the low roughness of the treated surface was achieved when treated with hexanite-R cutters. The roughness of the treated surface depends on feed, cutting speed, shape of the cutter tip, its wear and hardness of deposited layer. The depth of the surface hardening of the layer treated with cutters is greater than turning the weld materials of low hardness. During turning with hexanite-R cutters compressive residual stresses are formed in the surface layer, which improve the operating characteristics of parts.

The maximum permissiblse content of surface-active elements of carbon, nitrogen and boron in low-carbon Cr–Ni and Cr–Ni–Mo steels, which provide high resistance against intergranular corrosion (IGC) when tested in strongly and weakly oxidizing environments, was established. To ensure high resistance against IGC when tested in boiling 65% HNO₃ (according to ISO 3651-1), the carbon content in 03Kh18N11 (304L) and 03Kh17N14M3 (316L) steels should not exceed 0.025% and 0.015%, respectively, and when tested in boiling H₂SO₄ (ISO 3651-2, method B) should not exceed 0.03%. The nitrogen amount up to 0.2% does not influence negatively the IGC of the studied steels, and the simultaneous increase of nitrogen and carbon gives a negative synergistic effect. The negative influence of 0.003% and, to a greater extent, 0.03% boron on the grain boundary structure and resistance against IGC of steels hardened at temperatures >1100°C was shown. Technologies for increasing the resistance against IGC of pipes made of the studied steels were developed, taking into account the principle of grain boundary engineering of polycrystalline materials.

Physicomechanical characteristics of 15Kh16k5N2MVFAB-Sh steel (0.15C–16Cr–5Co–2Ni–0.7V–0.6Mo–0.3Nb–0.4N): wear resistance at 20°C and 500°C and resistance to fretting fatigue at 20°C without and with coatings obtained by the method of vacuum-arc deposition using targets based on the MAX phases of ({mathrm{Ti}}_{2}{mathrm{AlC}}) and ({{mathrm{(}{mathrm{Ti}}}_{1-x}{mathrm{Nb}}_{x})}_{2}{mathrm{AlC}}) , where x = 0.1 and 0.2, are investigated. At 20°C the friction coefficient and the wear specific rate of all coatings are greater than that of the studied steel in contact with a ShKh15 steel (1.0C–1.5Cr–0.3Ni–0.3Mn–0.3Si–0.25Cu) ball under a load of 2 N. Unambiguous relationship between microhardness and tribological characteristics of materials has not been recorded. The resistance to fretting fatigue of the samples with ({mathrm{Ti}}_{2}{mathrm{AlC}}) -based coating in contact with the Ni-alloy (17Cr–12W–11Fe–6Co–3Ti–1.5Nb–1.6Al) in high-cycle region (N > ({10}^{5}) cycles) is significantly higher than that of uncoated samples. The tribological characteristics of all materials decrease at 500°C but the least for samples with ({mathrm{Ti}}_{2}{mathrm{AlC}}) based coating. We have not found positive influence of niobium doping on the wear and fretting fatigue resistance of these coatings.

The inhibitory properties of an eco-friendly composition based on polysaccharide (gum arabic) and acetic acid salt (zinc acetate) to increase the corrosion resistance of D16T aluminium alloy in a neutral environment were investigated by electrochemical and gravimetric methods. It was established that the inhibitory efficiency of the composition increased with increasing concentration, and was maximally effective at 2 g/L of each component. The protective effect of the composition can be associated with the adsorption capacity of zinc acetate and gum arabic, due to the presence of hydroxyl and carboxyl groups in them, as well as the ability of Zn²⁺ cations to interact with OH^– anions, with the subsequent formation of zinc hydroxides, thus promoting blocking the cathode areas and slowing down the corrosion processes. It was shown that the degree of protection of the D16T aluminium alloy after 168 h of exposure to a 0.1% NaCl solution was 86 to 89%, which indicates the effective protective effect of the selected inhibitory composition.

The use of exothermic addition (EA) for charge in flux-cored wire is a promising way to improve technological characteristics of welded joints. The mathematical models to determine the charge density and the fill factor, which depend on the EA content, the ratio of graphite to EA oxidizer (CuO/C) and the ratio of the oxidizer to the aluminum powder in the composition of the EA (CuO/Al) were built. The investigated fusion modes depend mostly on such parameters: EA = 26–28 mass%, CuO/C = 4.0–4.5 and CuO/Al = 4.50–5.25.