An overview of our original studies and the results reported in the literature on the investigation of variations in structure, phase composition, mechanical and other properties of metallic ...materials under external impacts is made, including their high-pressure processing by large (severe) plastic and megaplastic deformation, explosion loading, and irradiation with ultra-short laser pulses.
This article presents a review of experimental investigations of changes in the structure and properties of the surface and near-surface layers of various materials (steels, metal alloys, ceramics, ...and graphite) in the area of a barcode applied by continuous laser radiation and short (nanosecond) and ultrashort (femto- and picosecond) laser pulses.
Laser shock peening with ultrashort laser pulses has been studied by hydrodynamic and atomistic simulations, as well as experimentally. It has been shown that, in contrast to traditional nanosecond ...pulses, ultrashort laser pulses allow one to increase the produced pressures by two or three orders of magnitude from 1–10 GPa to 1000 GPa (1 TPa). The physics of phenomena changes fundamentally because shock waves generating pressures exceeding the bulk modulus of a metal melt it. It has been shown for the first time that the shock melting depth at pressures about 1 TPa is an order of magnitude larger than the thickness of the melt layer caused by heat conduction. The appearance, propagation, and damping of a melting shock wave in titanium have been studied. The damping of the shock wave makes it possible to modify the surface layer, where the melting regime changes from a fast one in the shock jump to a slow propagation of the melting front in the unloading tail behind the shock wave. It has been shown experimentally that the ultrafast crystallization of the melt forms a solid layer with a structure strongly different from that before the action. The measured depth of this layer is in good agreement with the calculation.
In this work, the interatomic potentials for modeling diffusion in the C15 Cr2Ta Laves phase were constructed within the N-body approach. The potential for Ta–Ta interactions reproduces the lattice ...parameter, cohesive energy, elastic constants, equation of state, thermal expansion, point defect energies, and phonon dispersion of body-centered cubic Ta in qualitative agreement with density functional theory (DFT) data and almost quantitative agreement with available experimental data in the temperature range of stability of C15 Cr2Ta Laves phase. The potential for Cr–Ta interactions reproduces the elastic constants, point defect properties, equilibrium volumes, and formation enthalpies of Cr–Ta structures in qualitative agreement with DFT data. Also, it reproduces the lattice stability and high-temperature formation enthalpy of C15 Cr2Ta Laves phase in very close agreement with the available experimental data. The calculations of diffusion coefficients with constructed potentials showed that diffusion in C15 Cr2Ta lattice is governed by Cr atoms which cannot move without creation of vacancies. The constructed potentials can be used in further investigations of diffusion processes in Cr–Ta phases at temperatures up to 2000 K, while the obtained results on diffusion coefficients in C15 Cr2Ta Laves phase would be useful in the rational design of Cr–Ta based alloys.
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Tungsten, as the most refractory metal, is applied in fusion reactor in parts subjected to high temperatures and strong neutron irradiation. These factors lead to intense diffusion processes causing ...degradation of the material. Experimental investigations under such conditions are usually highly complicated and cannot provide a comprehensive understanding of the occurring phenomena. Therefore, their combination with theoretical approaches is required. One of the most robust approaches to simulate diffusion processes is molecular dynamics simulations based on classical interatomic potentials. It allows modeling relatively large samples consisting of several grains, grain boundaries, dislocations, and other types of defects for a reasonable computational time. The reliable simulations of the diffusion process require interatomic potentials satisfying the following criteria: prediction of melting point and thermal expansion as close as possible to the experimental values because the diffusion coefficient strongly depends on the homologous temperature and size factor. In the present paper, we present the new interatomic potential for tungsten, developed within the N-body approach, which reproduces the experimental value of melting temperature (3695 K) and thermal expansion at temperatures up to a melting point. The calculated diffusion coefficient demonstrates adequate agreement with experimental results. The constructed potential is applicable for simulation of processes involving diffusion, one of which is the irradiation damage.
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•We constructed new interatomic potential for W.•New potential is faster by two orders of magnitude than the GAP one.•Predicted self-diffusion coefficient in W agrees with the experimental data.•The diffusion coefficient deviates from Arrhenius equation at high temperatures.
Tungsten–copper alloys are heat-resistance materials for aerospace industry. Structure stability during processing and exploitation is controlled by the diffusion processes. In particular, the ...microstructure evolution is determined by the diffusion of copper atoms in tungsten matrix. Several experimental studies report different diffusivity of copper, which can be associated with the discrepancy of activation energy of diffusion depending on the structure of grain boundaries in tungsten. We performed density functional theory calculations of vacancy formation energies, segregation energies, and migration barriers for copper atoms in certain high-angle grain boundaries of special type using nudged elastic band method. Based on this information we calculated the corresponding diffusion coefficients. We found that the diffusivities in the studied grain boundaries exceed the extrapolated experimental data obtained at low temperatures at least by five times. The obtained data on diffusion path help to explain the depth, from which copper is removed during the annealing of the W–Cu alloy at 1500 K.
•We calculated formation energies of high-angle special grain boundaries in tungsten.•We calculated migration energies of Cu atoms in grain boundaries in tungsten.•We calculated vacancy formation energies in grain boundaries in tungsten.•Diffusion path of Cu is closer to the experimental data than previous results.
The effect has been studied of treatment with nanosecond laser pulses on the fatigue resistance of plate samples of recrystallized (grain size of the order of 2–3 pm) commercially pure titanium ...(grade VT1-0) under cyclic tensile loading. The results of investigations by scanning and transmission electron microscopy of the subsurface layer microstructure of the alloy under study after exposure to nanosecond laser irradiation and subsequent fatigue tests are presented.
One-dimensional quasi-periodic nanogratings with spacings in the range from 160 to 600 nm are written on a dry or wet titanium surface exposed to linearly polarized femtosecond IR and UV laser pulses ...with different surface energy densities. The topological properties of the obtained surface nanostructures are studied by scanning electron microscopy. Despite the observation of many harmonics of the one-dimensional surface relief in its Fourier spectra, a weak decreasing dependence of the first-harmonic wavenumber (nanograting spacing) on the laser fluence is found. Studies of the instantaneous optical characteristics of the material during laser irradiation by measuring the reflection of laser pump pulses and their simulation based on the Drude model taking into account the dominant interband absorption allowed us to estimate the length of the excited surface electromagnetic (plasmon-polariton) wave for different excitation conditions. This wavelength is quantitatively consistent with the corresponding nanograting spacings of the first harmonic of the relief of the dry and wet titanium surfaces. It is shown that the dependence of the first-harmonic nanograting spacing on the laser fluence is determined by a change in the instantaneous optical characteristics of the material and the saturation of the interband absorption along with the increasing role of intraband transitions. Three new methods are proposed for writing separate subwave surface nanogratings or their sets by femtosecond laser pulses using the near-threshold nanostructuring, the forced adjustment of the optical characteristics of the material or selecting the spectral range of laser radiation, and also by selecting an adjacent dielectric.
Microstructure of a thin (1–2 μm thick) subsurface layer of VT1-0 titanium alloy in the initial submicrocrystalline state and upon the action of nanosecond pulsed laser radiation has been studied by ...methods of scanning electron microscopy and transmission electron microscopy with an electron-probe microanalysis attachment.
