Tungsten is widely used as a material capable of withstanding working conditions in nuclear reactors and other extreme conditions. Under the influence of irradiation, such defects as Frenkel pairs, pores, and dislocation loops are formed in the metal. Therefore, the research aimed at studying the interactions of these defects with each other and their influence on the mechanical properties of the metal are relevant. The paper presents the theoretical study based on the molecular dynamics method, the purpose of which is to investigate the mechanism of strain hardening of tungsten associated with the interaction of dislocations and pores. The authors solved this problem using the LAMMPS package, carried out the integration of atoms motion equations by the fourth order Verlet method. The model under the study is a single crystal of a certain [111], [–1–12], [1–10] orientation along the basic X, Y, and Z coordinate axis relatively, in which the slip of edge dislocations in the main slip system of BCC metals and their interaction with pores is considered. The authors studied the influence of a pore size on the shear stress magnitude: the growth of pore diameter is proportional to the stress growth. The dependences of shear stress on the shear strain in the temperature range of 600–1400 K are calculated, whereby the temperature change does not significantly influence the stress value. The study shows that dislocations cut the pores and, upon the repeated interaction with a pore, a lower value of peak shear stress is observed than during the first one. The presence of pores leads to the flow stress increase, and such an effect becomes more evident with the increasing pore diameter. The flow stress increases thrice for pores with a diameter of 6 nm compared to the material without pores. The authors described the mechanism of interaction between the edge dislocations and pores under the influence of shear stress.

Simulation of crystal lattices under conditions far from equilibrium is an increasingly important subject of research and requires confidence in the validity of the applied interatomic potentials in a wide range of atom deviations from the balanced condition. To make such an assessment for modeling tungsten as an advanced material for various nuclear applications, the authors analyzed the nonlinear behavior of the lattice using several interatomic potentials. In a bcc tungsten crystal, oscillations were simulated according to the laws of several delocalized nonlinear vibrational modes – exact solutions to the equations of motion of atoms, the geometry of which is determined by the lattice symmetry at any amplitudes and does not depend on the type of interaction between the nodes. The authors considered two-dimensional cases of oscillations in one of the close-packed planes and three-dimensional cases when the motions of atoms have three components in space for a tungsten cell consisting of 2000 atoms and 31.6×31.6×31.6 Å in size. The amplitude-frequency characteristics of these modes were calculated for several interatomic potentials available in the LAMMPS library. The study identified that several interatomic potentials, namely eam.fs, set, Olsson, and Zhou show practically identical results, which is an indirect confirmation of their validity and the possibility of their use for modeling extreme impacts in the considered lattice. The authors calculated such characteristics of the system as kinetic energy, heat capacity, and pressure. Based on the results obtained, one can assume that mode 15, due to the modulation instability, will lead to the energy localization on individual atoms.

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