Materials Science最新文献

The mechanical characteristics and structural features of the heat-resistant 12Kh1MF steel after long-term operation in a bend of the TPP (thermal power plants) steam pipelines were analyzed. The change in the technical state of the metal of different zones of the bend and the anisotropy of properties across the pipe wall thickness were established. It was found that in the stretched zone of the bend near the outer surface of the pipe the steel degraded more intense than in other zones, which was due to the most favorable operating conditions for creep.

Hydrides of magnesium composites with additives of intermetallic TiFe and suboxide Ti₃Fe₃O were synthesized by mechanical milling in a hydrogen atmosphere. The addition of graphite reduces the particle size of the composites. The influence of catalytic additives and graphite on the hydrolysis of magnesium hydride was studied. The dependence of the amount of hydrogen obtained by hydrolysis on the time of composite milling was found.

Peculiarities of copolyimide modification by polyvinylpyrrolidone in a viscous state were studied. The differential scanning calometry revealed changes in the morphology and phase transitions of modified copolyamide materials. The increased technological compatibility between the components of copolyamide-polyvinyl pyrrolidone mixture was established. The effect of the modifier on the strength and thermophysical properties of the studied thermoplastic was found. Introduction of polyvinylpyrrolidone contributes to the growth of copolyamide strength under rupture and relative elongation and leads to a certain decrease in Vicat softening point and change of copolyamide technological properties.

Corrosion activity of a multi-component solution, namely, distiller liquid previously clarified and strengthened to 20 wt% by CaCl₂ including the addition of corrosion inhibitors at –5°C to low-carbon 08kp steel is studied by the gravimetric method. The holding time of the specimens is 500–650 h. In distiller liquid corrosion rate is 0.111 g/(m²×h), corrosion depth is 0.12 mm/year, steel resistance refers to the IV group (relatively resistant). When adding the hexamethylenetetramine, triethanolamine, trilon B corrosion inhibitors or their mixture in the amount of 0.5 wt% the corrosion resistance of steel improves, and the best results are achieved by adding hexamethylenetetramine with triethanolamine. The obtained results indicate the possibility of using the distiller liquid from sludge accumulator of JSC “Lysychanska Soda” with additives of such corrosion inhibitors as reagents for preventing highway surface against icing.

Polyurethanes (PU) are unique heteropolymers with a wide range of physicomechanical properties, fields of use and high development potential. PU is obtained by condensation of diisocyanate and various polyol compounds. The peculiarities of the structure and synthesis of commercial polyols based on the products of secondary oil processing, namely oligomeric glycols, oxides and dicarboxylic acids are presented.

The strength of the welded joint of the connecting pipe and the collector made of 12Kh1MF steel is investigated within the framework of the model of elastic solid, taking into account their real geometry and the dependence of the material characteristics on temperature. Zones of the maximum operating stresses in the joint for different types of welding are identified. Design and technological solutions aimed at significant reduction of the maximum operational stresses are proposed.

The results of experiments studying the dependence of contact angles for different initial clearances in a bolted joint on loading are presented. Considering the change of the interacting surface area of the composite plates with a pin, the bearing capacity of the hole is determined. The modified correlation algorithm for digital image processing is used to obtain the experimental results.

The microstructure of deposited layers with a composite material (CM) based on the self-fluxing PG-10N-01 alloy, modified with a mechanoactivated CM obtained using the self-propagating hightemperature synthesis, was studied. The X-ray phase analysis revealed in the deposited layer structure the inclusions of nickel borides NiB , Ni₂B , Ni₃B , chromium borides CrB , Cr₂B , chromium carbides Cr₃C₂ , Cr₇C₃ , distributed in the nickel matrix. The modifying CM during arc welding contributed to the grinding of structure and reduction of the friction coefficient, increase of the microhardness of the deposited coatings, and decrease of the wear intensity in various friction conditions.

It was established that the metal of long-term operated gas pipelines made of 10G2BT steel contains relatively little hydrogen, which does not create prerequisites for the pipes hydrogen embrittlement. However, for the considered cases, it was established that the microstructure of steel is characterized by increased defectiveness, which increases with the extension of the pipeline operation time. Such a defective microstructure has an increased ability of absorbing hydrogen, and therefore there is a risk of hydrogen embrittlement of the material. It was concluded that the use of long-term operated pipelines for transportation mixtures of natural gas and hydrogen without additional verification is problematic.

The dissolution of the metal surface layer of butt-welded joints samples made of 09G2S steel by the anodic-cathodic process in the electrolyte, as a result of which the geometric parameters of the welded joint changed, was studied. For example, after corrosion tests the radius of transition from the weld metal to the base metal on the facial side of the joint increased from 3.07 to 3.88 mm, and on its root, side increased from 2.16 to 3.09 mm. Changes in the geometrical parameters of a welded joint affect the value of the stress concentration factors (SCF), which determine fatigue life of the welded joints Therefore, analytical calculations of the SCF in the sample of the 09G2S steel butt-weld before and after dissolution of the metal surface layer were performed. In this case, the existing formula for SCF determination on the root side of the joint was modified for the case when the bases of facial and root reinforcements were close enough. It was found that after corrosion dissolution of the metal surface layer, the maximum value of the SCF in the specimen decreased from 1.87 to 1.67.