Russian Physics Journal最新文献

Recent publications of foreign and Russian researchers on the influence of niobium microalloying of pearlite steels and high-entropy alloys on their mechanical properties are briefly reviewed. The focus is made on the Nb effect on the microstructure and properties of rail steels and five-component (CoCrFeNiMn) Cantor alloys. The physical mechanisms of strengthening rail steels and high-entropy alloys are revealed and analyzed. An enhanced alloying effect in the case of a combined introduction of Nb + V and Nb + C into the high-entropy alloys is noted and interpreted.

The paper is devoted to a study of factors that provide the nonlinear mechanical influence of pore fluid on the stress state, strength, and fracture of permeable brittle materials. Two key factors are considered: pore pressure and viscous stresses in the interstitial fluid. Using a coupled dynamic model implemented in the numerical method of homogeneously deformable discrete elements, we verified for the first time that Stefan’s viscous stress is responsible for the nontrivial and widely discussed effect of a significant increase in the dynamic strength of brittle solids in a fluid-saturated state compared to the dry state. Considering watered high-strength concrete, a quantitative estimate of the dimensionless factor of Stefan’s stress was derived. The contributions of shearing and tearing-off fracture mechanisms to the total damage of a concrete sample under uniaxial compression with different strain rates are analyzed.

Using the methods of advanced physical materials science, the structural-phase states and properties of an ~80 μm-thick ribbon, made from a FeCoNiSiB high-entropy alloy of a non-equiatomic composition by ultrarapid quenching from melt, are studied. After the melt spinning the ribbon is in an X-ray amorphous state and demonstrates high strength and low plasticity. Anisotropy of its tribological properties is revealed. A differential scanning calorimetry of the ribbon is performed and its magnetic properties are evaluated.

This study investigates water absorption and porosity in the chitosan matrix reinforced with nano-biosilica, bamboo fiber, and jute fiber used for long bone material implants. The water absorption tests reveal distinct patterns in CP, CF, C1, C2, and C3 biocomposites, thereby highlighting the influence of their composition. Notably, 1% nano-biosilica reduces water absorption, yet increased nano-silica concentrations lead to heightened porosity. Striking a balance between optimal porosity for osseointegration and mechanical strength is crucial. Hybridization proves effective in mitigating water uptake and porosity. This study advances knowledge in biomaterial intricacies, providing crucial insights for tailored implant design.

The comprehensive approach using both pull-off tensile and scratch tests provided a detailed understanding of the adhesion and cohesion properties of the 3D-porous calcium phosphate (CaP) coatings deposited on a Ti substrate by the ultrasound-assisted micro-arc oxidation (UMAO) method. Using the pull-off tensile test which takes into account tensile stresses directed normally to the coating surface, it was found that the ultrasound (US) employing during the the micro-arc oxidation (MAO) process led to a slight decrease in the adhesion of the coating to the substrate from 23.4 to 19.3 MPa as well as to a change in the failure mechanism from the cohesive type characteristic for the control MAO coatings to the adhesive-cohesive type for the UMAO coatings. On the contrary, the results of the scratch test, which takes into account compressive stresses directed normally and tangentially to the coating surface, showed that the US employed during the MAO process led to an increase in the critical loads L_C2 and L_C3 to 6.7 and 30.6 N, respectively, promoting the adhesive-cohesive and adhesive failures of the coatings. Thus, the US employed during the MAO process led to an increase in the critical shear stresses of the UMAO coatings, thereby increasing their abrasion resistance.

The development of deformation and fracture in titanium alloy VT22 in the temperature range of 293–823 K is studied in the presence of ~0.1 wt.% hydrogen. It has been shown that the formation of the structure consisting of β-transformed grains with thin lamellar structure and particles of the primary α-phase increases the resistance of the hydrogenated VT22 alloy to localized plastic deformation at the macrolevel and promotes the transition of the alloy fracture from brittle-ductile to ductile during tension at room temperature. At elevated temperatures (653–823 K), the presence of dissolved hydrogen in the solid solution in the VT22 alloy reduces its resistance to localized plastic deformation at the macrolevel and the deformation value to failure.

The paper studies the electron irradiation at an energy of 30 keV affecting the diffuse-reflectance spectra and integrated absorption coefficient of solar irradiance of the micron-sized mZnO powder modified by adding nY₂O₃ nanoparticles in the amount of 0.1 to 10 wt.%. The best content of nanoparticles is found to be 3 wt.%, when the diffuse-reflectance spectra and the integrated absorption coefficient of the modified powder are 1.41 times lower than in the initial powder. It is shown that free electrons forming during the powder irradiation, make the highest contribution to the powder degradation.

The paper proposes a two-dimensional thermokinetic model of the composite synthesis process in the mode of dynamic thermal explosion taking into account the structurization of the synthesis product. Structurization in the model is understood as a transition from amorphous to crystalline state. The model takes into account the heating of the reactor walls by thermal radiation from the device, the temperature of which can vary at different rates. Chemical reactions are described by a summary scheme that corresponds to the synthesis of Ni₃Al composite. The kinetic law takes into account a possible strong inhibition of the rate of the reaction with the accumulation of the synthesis product, which is typical for reactions controlled by diffusion at the particle level. The effective thermophysical properties of the components of mixture and reaction products in the reactor depend on the properties of the constituents of the initial mixture and the fraction of reaction product. The properties of the latter also depend on the degree of structurization. The structurization process is described by a special additional parameter whose evolution is modeled by a reversible reaction. It is assumed that the structurization process starts from the moment of product appearance and continues during the cooling of the system. It is shown that synthesis results in the formation of a composite containing the initial components and the reaction product with the matrix partly in the amorphous state and partly in the structured state. The dynamics of synthesis and structurization are influenced by heating conditions and reactor size.

The paper presents calculations of the process parameters of the chemical isotope exchange with a thermal flow reversal in the BF₃–C₆H₅OCH₃ system and engineering data for rectifying columns for its implementation. It is shown that the calculated parameters are in good agreement with those found the literature. The best engineering data are obtained for rectifying columns intended for the production of enriched (96 wt.% ¹⁰B enrichment) boron in the amount of 2 and 4 tons per year.

Using the methods of transmission and scanning electron microscopy, the microstructure of a V–W–Cr–Zr alloy is studied as a function of its plastic deformation value under the condition of high-pressure torsion in the Bridgman anvils. The main stages of structure transformation and the respective mechanisms are identified. It is found out that the grain and defect structure transformation up to e ≈ 1.1 is provided by the dislocation and dislocation-disclination mechanisms, which when combined activate the processes of submicrocrystalline structure formation. The deformation impact in the strain interval from e ≈ 1.1 to e ≈ 3 is characterized by a significant increase in the grain-boundary length. A high strength state is achieved in the course of this deformation, where the dislocation modes of plastic deformation are suppressed. This is accompanied by the activated processes of formation of two-level nanostructured states, wherein the principal mechanism is a quasi-viscous re-orientation by the flows of non-equilibrium point defects. A further increase in the deformation to e ≈ 5.3 gives rise to refinement of the submicrocrystalline grains and formation of two-level nanostructured states in the entire material volume. The main contribution to the grain- and subgrain transformations comes from the disclination and quasi-viscous modes of plastic deformation. At higher strain degrees (e > 5.3), the size of submicrocrystalline grains does not virtually change, and the transformation of two-level nanostructured states makes itself evident in the rotations of some of the fragments of this structure with respect to the other by small angles from tens of fractions of a degree to several degrees. The formation of the submicrocrystalline state is followed by a multiple increase in the microhardness; its values are observed to saturate at e ≈ 3.3.