Materials Science最新文献

Using the energy approach, a calculation model was built to determine the period of subcritical growth of a system of cracks in metal plates, subjected to long-term static tension and local electrochemical corrosion. The effect of a corrosive environment on the residual life of a plate with a system of periodic and doubly periodic cracks was evaluated.

A brief overview of studies on the influence of inclusions on the mechanical properties of structural materials was performed. The studies, where analytical dependences were obtained for predicting the mechanical properties of structurally heterogeneous materials (ultimate strength, fatigue limit, and crack growth resistance) depending on the shape, volume content, and size of inclusions, were mentioned.

Factors, which cause fracture of reinforced concrete constructions of bridge structures were considered. One of them is anti-icing material used for road safety in the winter period. The Ukrainian market of anti-icing chemical reagents and combined agents of natural and industrial origin was analyzed. The kinetics of corrosion fracture of 09G2S and St3 steels as the main material of reinforcement in neutral chloride-containing and alkaline solutions was investigated using the method of polarization resistance. Taking into account the kinetics of corrosion fracture of the studied steels, the rate of their general corrosion was calculated.

Mechanical and corrosion properties of Fe–B–C alloys (0.1–9 wt% B; 0.2–4 wt% C; Fe is balance) were investigated. Microhardness and compressive strength, resistance to abrasive, and gas-abrasive wear of the alloys were determined at room temperature. The corrosion rate was measured by gravimetric method in the following aqueous solutions: 0.5 M H₂SO₄ , 5 M H₃PO₄ , 0.8 M HNO₃ , 1 M HCl , 2 M CH₃COOH , 3 M NaCl, and 0.2 M Na₂SO₄ . The highest resistance to abrasive wear is shown by Fe–B–C alloys with high hardness and the highest resistance to gas-abrasive wear – by the alloys with high compressive strength. In a majority of the acidic and neutral media, the corrosion rate of Fe–B–C alloys decreased with increasing time due to the accumulation of corrosion products on the surface of the samples. The corrosion rate increased with an increase in the volume fractions of eutectic and austenite phases in the eutectic colonies or when interfaces between the primary and peritectic phases were formed in the structure. The Fe–B–C alloys demonstrated the highest corrosion resistance in the sodium chloride solution and the lowest one in the nitric acidic solution.

A laboratory method has been developed to investigate the gaseous hydrogen effect on the intensity of electrochemical processes on pipe steels under the action of a model medium simulating condensate at the pipe’s inner surface. It is based on the measurement of electrochemical parameters of steel under conditions of gaseous hydrogen bubbling and simulates operating conditions when hydrogen saturates a thin layer of condensate inside the pipe. On the example of API 5L X70 pipe steel significant effect of hydrogen on its electrochemical behavior under such conditions is established. It is concluded that the saturation of the model medium with hydrogen significantly accelerates the corrosion of steel and its hydrogenation.

The results of the experimental study of the degradation of steel structures of sewer underground constructions are presented. The distribution of harmful gas elements (sulfur, hydrogen, oxygen) over the wall thickness of sewer pipes along corrosion defects in the form of pits, as well as the character of changes in the microhardness of the metal depending on the hydrogen content and service life, are shown. To confirm the metal softening with increasing hydrogen concentration, the stresses of the crystal lattice (distortion stresses) were measured.

The results of thermal calculations of the part of the fuel assembly of the active zone of the VVER-1000 reactor in the stationary mode of operation make it possible to evaluate the mechanical state of the fuel rod cladding, to understand the influence of reactor control methods on the strength and the design acceptance criteria. The main principles of the evaluation of mechanical characteristics of VVER-1000 fuel rods using the START-3 code are presented. The results of the prediction of the mechanical characteristics of the VVER-1000 fuel rods during the 4-year cycle in stationary mode under normal operating conditions and under their violation are illustrated. The maximum values of stress in the fuel rod in the stationary mode of operation are in the range of 60–80 MPa, which cannot cause depressurization of the fuel rod.

The change in the structure and physicomechanical properties of sintered binding WC–6Co, and WC–15Co cemented carbides because of the action of high pressure (8 GPa) and high temperature (HPHT) in the Toroid installation is investigated. It is established that as a result of HPHT treatment at temperatures above the melting point of the metal binding phase, there is a decrease in the coercive force of the experimental alloys due to the growth of the carbide grain of the alloy. In alloys with a higher content of the binding phase, Co₃W, Co₆W₆C intermetallic phases, and oxide of the Co₂O₃ type are formed. The hardness of the HPHT treated WC–6Co alloy samples decreases due to the growth of the alloy carbide grain, and the hardness of the treated WC–15Co samples increases due to the formation of intermetallic phases.

The influence of the elemental composition of strip amorphous alloys Fe_80.0Si_6.0B_14.0, Fe_78.5Ni_1.0Mo_0.5Si_6.0B_14.0; Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4; Fe_51.7Ni_21.7Cr_6.2Mo_0.6V_1.5Si_5.2B_13.1 on corrosion resistance in 0.5 M aqueous solutions of NaCl, HCl, and KOH at T = (293 ± 1) K was investigated. The high corrosion resistance of Fe_51.7Ni_21.7Cr_6.2Mo_0.6V_1.5Si_5.2B_13.1 and Fe_73.1Cu_1.0Nb_3.0Si_15.5B_7.4 alloys in aggressive environments was established. Electrochemical parameters obtained both by the method of cyclic voltammetry and electrochemical impedance spectroscopy (EIS) indicate the formation of more durable surface layers in a 0.5 M potassium hydroxide aqueous solution on these alloys. The Cl^– ions (especially at low pH) under their long-term action are the more aggressive oxidizers of amorphous alloys compared to OH^– ions. During the passivation film formation in highly aggressive environments such alloy elements, which do not participate in this process, actively dissolve, and the main film-forming elements accumulate under the film, thus improving its protective properties.

The impact toughness of each component (fibreglass shell and carbon-plastic core) of the composite pump rod was evaluated, and the fractographic peculiarities of the impact-tested samples fracture were investigated. The fibres inside the rod shell are fractured by a brittle cleavage mechanism and the polymer matrix by a ductile mechanism, with its failure into small fragments. A specific feature of the rod core is strips of unidirectional carbon fibres with periodic reorientation, with the change of crack propagation direction at the transitions between adjacent strips. This structurally conditioned reorientation of the fracture surface inside the rod core retarded the fracture of both the core material and the rod as a whole.