Russian Physics Journal最新文献

The paper demonstrates the influence of the thickness of the 2024 aluminum alloy plates on the effectiveness of active liquid cooling during friction stir welding. The obtained results indicate that active liquid cooling improves strength properties of the 2024 aluminum compared to air cooling. The highest efficiency of liquid cooling is achieved in welding thin (2 mm) metal plate. It is shown that the effectiveness of liquid cooling decreases with increasing thickness of welded plates.

The results of a study focused on the separation of contributions into the increasing the radiation resistance of the micro powders modified with micro- and nanoparticles of oxide compounds with the rare earth cations are reported. It is found out that the relaxation of primary defects formed by irradiation occurs in two pathways: relaxation on nanoparticles—crystal lattice structure defects of the CaSiO₃ micropowder, and relaxation on the cerium dioxide cations, the rare earth elements with an incomplete f‑shell. The former mechanism provides a larger contribution into the radiation resistance: it decreases the concentration of the irradiation-induced primary radiation defects on nanoparticles, as on the small-sized defects in the micro powder crystal structure. The relationship is fulfilled in a wide range of the fluences of the electrons with the energy of 30 keV (F = (1–7) ∙10¹⁶ cm⁻²). Similar relationships were determined earlier for the ZnO powder modified with Gd₂O₃ micro- and nanoparticles.

The paper focuses on the fabrication of Stellite 6 alloy using wire-feed electron beam additive manufacturing (EBAM) with different electron beam sweep parameters. Three types of sweep patterns are studied: ellipse, figure-eight across the forming layer, and spiral from the center. Three different scanning frequencies are applied to the ellipse sweep pattern: 100, 200, and 500 Hz. It is shown that sweep parameters significantly affect the final geometry of the EBAM-manufactured samples. It also helps to suppress the size growth of the dendritic arm, as the height of obtained samples increases. It is demonstrated that varying sweep parameters does not affect the structure and phase composition and thus the mechanical properties of fabricated samples.

The wear of the tool made of a ZhS6U heat-resistant nickel alloy during friction stir welding of a high-strength titanium alloy is analyzed. A metallographic analysis of the formed joints reveals the traces of intermetallic compounds of titanium and nickel. An X‑ray phase analysis confirms their presence both in the formed permanent joints and on the tool surface. A visual analysis of the tools and their measurements after welding show that the tool pins have experienced the most severe wear.

Using the method of active tension, the short-term strength and plasticity characteristics are determined for vanadium and its alloy in a low-temperature region. The peculiarities of neck formation and material fracture are studied as a function of the tension temperature and the initial structural-phase state. It is found out that the vanadium specimens demonstrate V‑shaped fracture profiles and a rough relief along the grain boundaries on the lateral surfaces. Irrespective of the mode of thermomechanical treatment of the V–Ta–Cr–Zr alloy, there are strain localization regions formed at all of the tensile test temperatures, which measure a few hundred micrometers along the axis of tension. It is observed that prior to the neck formation the strain localization becomes more rapid. It is shown that the plastic deformation and fracture of the V–Ta–Cr–Zr alloy at cryogenic temperatures do not depend on its structural-phase state. It is hypothesized that the grain size and the polygonal state act together as the decisive factors in the processes of strain localization and neck formation under the tensile conditions at the temperatures of −50 and −100 °C.

The paper studies the aluminum (Al) and gallium (Ga) mixture combustion in a closed reactor under a 5 MPa pressure of gas nitrogen. Investigations include the influence of the gallium content in the initial Al-Ga mixture on the amount of absorbed nitrogen, combustion rate, maximum combustion temperature, and phase composition of the products obtained. The paper investigates the microstructure of the nitrided product based on a mixture of 50 wt.% Al and 50 wt.% Ga. The increased Ga content in the initial mixture leads to a decrease in the maximum combustion temperature, combustion rate, and the amount of absorbed nitrogen. When the gallium content in the initial mixture exceeds 70 wt.%, the combustion reaction fails in self-propagating synthesis. After nitriding the Al and 10 wt.% Ga mixture in the combustion mode, the obtained products consist of the AlGaN phase. At 70 wt.% Ga, the AlGaN phase stoichiometry ranges from Al_0.99Ga_0.01 N to Al_0.85Ga_0.15N. The structure of the obtained products consists of shapeless particles, globules, and elongated bars comprising lamellas. The Al‑, Ga- and N‑based compound is present in the form of shapeless particles.

A study of the high-strength titanium alloy VT23 (Ti-6Al-5V-2Mo-1Cr-1Fe) after its friction stir welding and friction stir processing is performed at different parameters. The metallographic research shows some microstructural changes in the metal after this friction stir technological processes. The mechanical tests of the weld joints and processed material show a decrease in the ultimate strength. The XRD analysis confirms the phase changes in the high-strength titanium alloy.

The effect of Nb alloying (10 at.%) on the B2–B19′ thermoelastic martensitic transformation and the corrosion resistance of Ni_49.5Ti_35.5Hf_15.0 (at.%) alloy in seawater substitute is studied. An addition of Nb suppresses the precipitation of (Ti,Hf)₂Ni-phase particles and results in the formation of β‑Nb phase particles, and the martensitic transformation is accompanied by high elastic energy storage. The Nb alloying in conjunction with a single crystalline state of the NiTiHfNb system significantly increases its corrosion resistance. Upon introduction of Nb, the corrosion rate decreases by a factor of 1.2 in polycrystals and by 5.2 times in single crystals compared to that in Ni_49.5Ti_35.5Hf_15.0 polycrystals. This corrosion behavior is attributed to the formation of a more stable passive oxide film consisting mainly of Nb oxides. Pitting corrosion is observed in polycrystals and single crystals of (Ni_49.5Ti_35.5Hf_15.0)_90.0Nb_10.0 alloy, and its structural features depend on the morphology of the β‑Nb phase. Corrosion occurs in the matrix, while the exposed β‑Nb phase is coated with niobium oxide, which prevents pitting.

The paper focuses on the curing kinetics of Portland cement as a non-equilibrium condensed matter in the temperature gradient of 65 to −20 °C. The finite element method is used for 2D modeling of Portland cement curing based on the modified Wang model and the analysis of cement hydration processes and its physical and mechanical properties during a transition from one stage to another (incubation → diffusion → acceleration → retardation). Localized temperature gradients hinder hydration at the cooled (T = −20 °C) end of the cement rod, where phase transitions are not completed in some regions. Exothermic reactions act as distributed heat sources, creating reflected heat flows (analogs of reaction and diffusion processes in disordered systems). It is found that the maximum von Mises stress (up to 2.5 МPа) occurs at the interface between the cement rod and thermal insulation and in regions with T < 0 °C, where superposition of direct and reflected heat flows leads to critical strains. Stresses exceed the elastic strength of the material that corresponds to the crack nucleation theory in condensed matter with inhomogeneous structure.

This study proposes a novel numerical solution method for the nonlinear one-dimensional Fisher equation, which involves complex and important physical issues concerning the heat conduction and combustion theory. This algorithm adopts a direct meshless technique based on the configuration point method, breaking through the traditional two-level computing framework by introducing combined radial basis functions. The nonlinear Fisher equation with time-varying characteristics can be transformed into a one-level solving problem. Numerical experiments verify advantages of this method in terms of the computational accuracy and efficiency by solving the Fisher equation and modified Fisher equation. Compared to traditional time stepping methods, this one-level solution architecture significantly improves the computational stability with the high solution accuracy.