Materials Science最新文献

Hydrides of magnesium composites with additives of TiFe intermetalide and Ti₃Fe₃O suboxide was synthesized by mechanical milling in hydrogen. The rate of mechanochemical hydrogenation of magnesium in the presence of these additives doubles, and the temperature of hydrogen desorption decreases by 100…150°C. With the addition of graphite, the particle size of the composites decreases, and the rate of formation of magnesium hydride during milling and in subsequent cycles of hydrogen sorption-desorption increases. The properties of composites, depending on different initial particle sizes and magnesium purity, were investigated. Composites based on magnesium chips were synthesized using a simplified method.

The structure of deposited layer based on the Fe–Ti–Mo–B–C system is investigated. A methodology for 3D modeling of the Fe(Mo, B)₂ phase grain, which includes four stages, was developed. Blender software was used for 3D modeling, and the Image Pro Plus software was used for image analysis and measurements. The results show that in the Fe–Ti–Mo–B–C deposition, the main strengthening Fe(Mo, B)₂ phase was formed around TiC grains, which act as modifiers.

An acoustic-emission method for determining the residual life of power equipment with hightemperature creep cracks under long-term static tensile load has been developed. This method is based on the method, previously proposed by the authors, of constructing a reference acoustic-kinetic diagram of the propagation of a high-temperature creep crack in the same material as the object under study, as well as a scheme of a reference analytical acoustic pattern (acousogram) during crack propagation. The essence of the method is as follows. It is believed that the object fracture takes place by the propagation of already existing plain cracks in it, near which there are normal tensile stresses. It is proposed to determine the initial area of the crack and the load of the object based on the parameters of the acousogram recorded during crack propagation in the investigated object. The numerical experiment was conducted to demonstrate the application of this method.

Most carpal bone fractures occur in the scaphoid. The most suitable size of NiTi shape memory alloy (nitinol) staples to heal scaphoid fractures was found by comparing two commercially available compression staples (DynaClip™ Bone Fixation System, 10×10 and 14×14 mm). The scaphoid bone was selected for simulating a model in SolidWorks software. To accurately investigate the effect of staple size on the bone the scaphoid was assumed to be a three-layer composite structure consisting of collagen and mineral crystals. The stress distributions along a path located at the waist of the scaphoid were assessed. The finite element analysis was carried out in ABAQUS software based on the nitinol staple shape memory effect and super-elasticity behavior. The results indicated that the smaller size of staples induced a more significant stress on the central zone of the scaphoid, whereas the larger size of staples showed a peak stress concentration on the peripheral zones with a reduced stress concentration at the center. Hence, it is suggested to utilize the two of these staples in different orientations or in parallel with each other to improve the biomechanical behavior of the regenerated bone.

Corrosion behavior of electrolytic binary and ternary alloys in the 1 M KOH solution deposited from citrate-pyrophosphate electrolytes is studied. Based on the performed impedance measurements, the formation of a dense oxide layer which blocks the access of the electrolyte to the metal through cracks and pores is shown. Equivalent schemes have been selected and substantiated, and the parameters of the corrosion process have been calculated for 9 days of the samples exposure to the corrosive solution. Using chemical mapping it is shown that the corrosion product is predominantly cobalt oxide. A ternary alloy is characterized by a higher initial corrosion resistance of 6 kΩ×cm^–2 and a significant polarization resistance after slowing down and stabilization of the corrosion process – 37 kΩ×cm^–2.

Assessment of the efficiency of two-phase titanium alloys gas nitriding was carried out using metallographic, XRD and durometric analyses. It was ascertained that the higher the β-stabilization factor, the lower the intensity of nitride formation and gas saturation during nitriding. The lowest nitriding efficiency corresponded to VT22 high-alloyed titanium alloy with the highest β-stabilization factor. The main technological (thermocycling) and structural (preliminary deformation or laser treatment) approaches to improve the nitriding efficiency were analyzed.

The aluminum-based coating was sprayed onto a substrate made of MA5 magnesium alloy by detonation and thermal vacuum methods. Potentiodynamic polarization studies were carried out to evaluate corrosion resistance of the modified surfaces. Thermal vacuum coating is non-porous, but thin (approx. 50 μm). The plasma-electrolytic oxidation (PEO) layer of the aluminum coating almost does not interact with the magnesium base during the process of synthesizing the oxide ceramic coating. The corrosion resistance of the detonation coating was twice as high as that of the MA5 magnesium alloy, but the layer synthesized on the PEO coating neutralized this effect. This is related with the growth of the PEO layer through the sprayed coating (thickness approx. 200 μm) to the base and the presence of through pores in it, which over time causes the spalling of such a combined coating. The opposite electrochemical picture is observed on the surface of the thermal vacuum sprayed coating without and with the presence of the PEO layer on it. Here the corrosion currents are lower in 25 times and by 2 orders of magnitude, respectively. Such a significant difference in the corrosion resistance of aluminum coatings is caused by their porosity and structural defects due to the peculiarities of the technological process.

Wear-contact of two elastic half-planes (plain deformation), the surface of one has periodic sloping protrusions of cylindrical shape under local wear on the basis of the frictional-fatigue fracture model is investigated. The formulated contact problem is reduced to a singular integro-differential equation with a Hilbert nucleus with respect to the thickness of the worn material and equations for determining the unknown areas of wear. The shape of the protrusions and contact pressure at the beginning and after wear are analyzed.

The 2.3-diaryl-4.5-dihydro-imidazo[1.2-a]quinolinium-3 bromides were tested as biocides and inhibitors of microbial corrosion of low-carbon steel induced by bacteria of Desulfovibrio sp. M-4.1 strain. The degree of metal protection against corrosion induced by sulfate-reducing Desulfovibrio sp. M-4.1 bacteria was 84.6–92.4%. 2-(para-tolyl)-3-(41-methoxyphenyl)-4.5-dihydro-imidazo[1.2-a]quinolinium bromide demonstrated the best protective effect. It was established that sulphate-reducing bacteria of Desulfovibrio sp. M-4.1 strain were sensitive to 2.3-diaryl-4.5-dihydro-imidazo[1.2-a]quinolinium-3 bromides. Under the influence of imidazoquinolinium quaternary salts, the inhibition zones of bacterial growth have the diameters of 24.7–45.5 mm. Quaternary salts of imidazoquinolinium completely suppress the growth of sulfate-reducing Desulfovibrio sp. M-4.1 bacteria in plankton and significantly influence the formation of biofilm (the number of cells decreases by 6–8 orders compared to the control sample) under conditions of microbial corrosion. Suppression of the sulfate-reducing activity of Desulfovibrio sp. M-4.1 bacteria by quaternary salts of imidazoquinolinium (by 88.8–91.6%) was proven. The effectiveness of the quaternary salts was discussed with the account of molecular descriptors.