Bulletin of Perm University. Physics

Evolution of texture and residual stresses after laser shock peening in titanium alloys VT6 and VT1-0

2025-11-13T09:02:01+00:00

The paper investigates the effect of laser shock peening (LSP) on the evolution of the crystallographic texture and residual stresses of titanium alloys VT1-0 and VT6. The research purpose was to study changes in the X-ray spectrum and texture before and after LSP with the use of X-ray diffraction and MTEX software package for analyzing complete pole figures. The samples were subjected to laser treatment with the following parameters: wavelength – 1064 nm, pulse energy – 1 J, pulse duration – 10 ns. The results have shown that the texture of VT1-0 alloy is characterized by heterogeneity. A gradient of maximum pole density is observed, which increases from 2.6 in the central part of the leaf to 3.2 in its marginal zone. After LSP, there was noted a decrease in the texture sharpness at the edge of the leaf (mrd decreased to 2.6), while in the center the changes were insignificant. For VT6 alloy, the texture turned out to be initially weak (mrd ≈ 1.3), and LSP did not cause its noticeable transformation. It is shown that the peaks of the diffraction spectrum widen for VT6 and VT1-0 alloys, which is associated with the deformation of the crystal lattice and changes in the magnitude of residual stresses.

The motion of the axis of a large-scale vortex flow of liquid metal in a disk cell caused by low magnitude azimuthal electromagnetic force with non-linear radial distribution

2025-11-13T09:08:40+00:00

Laminar flow of liquid metal caused by axisymmetric electromagnetic force with non-linear radial distribution is studied numerically. Electromagnetic force is defined by the vector product of current density and orthogonal magnetic induction. Non-linear radial force distribution with maximum occurs when electric current is applied to the central region of the cell and discharged through the periphery while magnetic field is created by Helmholtz coils with a diameter less than that of the cell. Numerical simulation was conducted in ANSYS Fluent. It has been discovered that, in a certain range of parameters, the axis of the rotating liquid-metal flow starts oscillatory motion relative to the center of the cell. This effect appears in the occurrence of secondary flows such as Görtler vortices, Ekman pumping, and Kelvin-Helmholtz instability. The boundary between the regions of the absence and occurrence of a large-scale vortex oscillation has been found in the space of geometric and force parameters.

Generation of an average flow by a semi-submerged oscillating sphere

2025-11-13T09:13:32+00:00

The paper presents the results of an experimental study into the structure of an average flow generated by a semi-immersed oscillating sphere. The average flow in the considered situation is induced by (1) an inhomogeneous viscous boundary layer on the submerged part of the sphere, generating an axisymmetric flow with a pronounced jet from the lower pole of the sphere, and (2) a traveling surface wave drifting the subsurface liquid layer in the direction of its propagation. The paper is mainly focused on the flow induced by the wave mechanism and on the change in its structure depending on the characteristics of the vibrations and the state of the interface associated with the presence or absence of an adsorbed layer of a surfactant on the surface. The wave configuration and the structure of the average flow were investigated in experiments. The main part of the experiments was carried out with isopropyl alcohol, which excluded the formation of an adsorbed layer. It has been found that a traveling cylindrical wave generates an axisymmetric centrifugal flow along the interface, the intensity of which grows with increasing amplitude of vibrations. When the amplitude exceeds a critical value, the cylindrical wave becomes unstable, which results in the formation of two spiral waves propagating in opposite azimuthal directions and having the frequency two times less than the oscillation frequency of the sphere. The amplitude of the resulting wave turns out to be modulated in the azimuthal direction, as a result of which the radial flow velocity also turns out to be a periodic function of the azimuthal coordinate. Additionally, a series of qualitative experiments with water of various purity degrees was carried out to determine the effect of the adsorbed surfactant layer on the structure of the average flow. It is shown that the presence of a surfactant leads either to complete immobilization of the surface or to the formation of a multi-vortex flow on the interface, depending on the surfactant content. In conclusion, the results obtained are compared with the data reported in earlier studies on the problem under consideration.

An experimental study into the mechanisms of hydro- and sonoluminescence and initiation of microexplosive fuel atomization

2025-11-13T09:23:32+00:00

We have experimentally studied hydro- and sonoluminescence phenomena during the flow of hydraulic oil in a narrow channel, with an original experimental setup used. The study substantiates the assumptions that liquids, being condensed media, can exhibit mechanisms of quasi-plastic momentum transfer at strain rates of έ > 10⁵ s^-1. One of the manifestations of localized shear in liquids upon reaching shear rates of έ > 10⁵ s^-1 in the near-wall region is hydroluminescence. It has been experimentally established that there is a threshold value of the strain rate έ ~ 10⁵ s^-1 (Re ~ 1350, ∇P ~ 1.2 GPa/m) at which a sharp increase in the intensity of hydro- and sonoluminescence signals is observed. The proposed designs of measuring cells made it possible to separate signals characteristic of hydro- and sonoluminescence manifestations. Statistical processing of signals obtained from a photomultiplier allowed us to establish differences in the laws of distribution of hydro- and sonoluminescence pulses, which confirms the qualitative differences in the phenomena under study. Hydroluminescence is caused by the implementation of a pseudoplastic momentum transfer mechanism in liquids, while sonoluminescence is associated with cavitation mechanisms. In conclusion, recommendations are proposed concerning the manufacture of fuel injector channels for initiating microexplosive fuel atomization by activating ‘hot spots’ associated with localized shifts in liquids.

The influence of the substrate surface heterogeneity on axisymmetric oscillations of a drop in a finite volume of liquid

2025-11-13T09:26:45+00:00

The article deals with the influence of substrate properties on drop dynamics in a vibration field. Natural and forced oscillations of a liquid drop surrounded by another liquid in a cylindrical vessel of a finite volume are investigated. In the equilibrium state, the drop has the shape of a cylinder and is limited in the axial direction by two parallel solid surfaces. The dynamics of the contact line of three media (drop–liquid–solid surface) is taken into account: the velocity of the contact line is proportional to the deviation of the contact angle from its equilibrium value. The proportionality coefficient (wetting parameter) is a function of the substrate surface coordinates, which allows us to consider this surface as inhomogeneous. The vessel is exposed to a vibration force directed along the symmetry axis of the vessel. Such vibrations excite only axisymmetric oscillations of the drop, but, due to the inhomogeneity, azimuthal modes will be excited, the spectrum of which is determined by the type of inhomogeneity. The dependence of frequencies and damping decrements of natural oscillations on the parameters of the problem is investigated. It is shown that heterogeneity qualitatively changes these dependences in comparison with the case of a homogeneous surface. The study of forced oscillations has revealed clearly noticeable resonance effects. It is shown that resonance frequencies of azimuthal modes are present.

Calculation of the freeze wall thickness under high external loads

2025-11-13T09:31:49+00:00

In practice, the required thickness of freeze walls (FWs) is typically calculated using formulas based on the Mohr–Coulomb (MC) strength criterion. However, applying such formulas to determine FW thickness in water-saturated rocks at great freezing depths may lead to significant errors due to the nonlinearity of the failure envelope of Mohr’s circles. This study analyzes the functional form of nonlinear relationships between the maximum shear stress (corresponding to the failure state) and the mean normal stress for various rock types. A classification of rocks (sand, clay, siltstone) is proposed based on the functional form of the approximating formulas representing the nonlinear failure envelope of Mohr’s circles. A numerical solution was obtained for the limit stress state of an FW in siltstone at –6 °C under varying external loads applied to the outer wall of the FW. This solution was compared with the classical solution by S. S. Vyalov; as a result, we have identified the conditions and boundaries within which classical FW thickness formulas, based on the linear MC criterion, remain valid. A new formula was derived for determining FW thickness under external load with taking into account the nonlinear behavior of the failure envelope of Mohr’s circles.

Investigation of the influence of gas-dynamic spraying parameters on the quality of thin films of transparent conductive oxides

2025-07-18T15:31:13+00:00

Transparent conductive oxides (TCO) are widely used in modern optoelectronics due to the unique combination of high electrical conductivity and optical transparency in the visible spectrum range. The spray pyrolysis method is one of the most promising technological processes for obtaining thin-film TCO coatings; however, the quality of the resulting films critically depends on the gas-dynamic spraying parameters. The paper investigates how the carrier gas velocity, spraying pressure, substrate temperature, and precursor concentration influence the morphology, crystal structure, and electrophysical properties of thin films of indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO). The study employed the methods of X-ray diffraction analysis, optical spectroscopy, and four-probe measurement of electrical conductivity. It has been established that the optimal carrier gas velocity is 2.5-3.0 l/min at a pressure of 0.15-0.20 MPa for obtaining ITO films with minimum resistance (8.2×10^-4 Ohm·cm) and maximum transparency (88% in the visible range). Increasing the substrate temperature from 350°C to 450°C leads to improved film crystallinity and a 40% reduction in resistivity. The mathematical model of the process showed a correlation between the Reynolds number of the gas flow and film thickness uniformity. The obtained results demonstrate the critical importance of optimizing gas-dynamic parameters for obtaining TCO thin films. The developed mathematical model allows predicting film properties depending on technological parameters and can be used to optimize industrial processes for producing transparent electrodes for solar cells and displays.