Vol 124, No 9 (2023)

We simulate structure in the vicinity of different size nanovoids using a new variant of the Molecular Statics, wherein atomic structure in the vicinity of nanovoids and the parameters that define the displacements of atoms placed in elastic continuum around main computation cell are determined in a self-consistent manner. Then, the previously obtained kinetic equations are applied to calculate the shifting rate of the elements of the void surface in certain crystallographic directions. These equations take into account the dependence of the vacancy flux on the deformation fields. The displacement rates in different crystallographic directions for bcc and fcc metals are significantly different. The results show that the effects studied by computer simulation can lead to a change in the shape of initially spherical nanopores and cause their transformation into cuboidal pores in metals with a cubic structure under irradiation.

Gadolinium oxide nanoparticles were obtained by the spark discharge electrophysical method. Structure, magnetic and magnetocaloric properties of Gd2O3 nanoparticles are comparatively analyzed. According to X-ray phase analysis, the synthesized Gd2O3 nanoparticles contain two crystallographic phases: cubic and monoclinic. The change in the magnetic part of the entropy dSM was determined from the measurement data of magnetic isotherms based on the Maxwell relation. The maximum value of dSM for a magnetic field variation amplitude of 2 T was approximately 17 J/kgK and was observed at a temperature of 2.5 K.

The critical cooling rates required for suppression of Fe40Ni40P14B6 melt crystallization were estimated in the framework of the formalism of classical theory of crystallization assuming homogeneous nucleation rate, linear isotropic growth and Kolmogorov-Johnson-Mehl-Arami kinetics. Both the calculated “time-temperature-transformation” diagrams and the integral form of the Kolmogov’s equation for the case of continuous cooling were used for the estimations. The temperature dependences of the rates of crystal nucleation and growth were calculated with using of the values of the thermodynamic and kinetic parameters governing the crystal formation in amorphous phase as well as with the three-parameter temperature dependence of diffusivity proposed in the study. The critical cooling rates for different combinations of the equations describing nucleation and growth of crystals were estimated and the conditions for the correct prediction of the glass forming ability of Fe40Ni40P14B6 melt were established.

This paper presents the results of a study of the stability of a supersaturated solid solution (SSS) of sheets made of thermally hardened aluminum alloy of the Al-Mg-Si system with a small addition of copper (Al-0.6Mg-1.0Si-0.2Cu) under various quenching modes. The samples were subjected to isothermal or continuous quenching with different quenching cooling rates, after which artificial aging was carried out at a temperature of 170°C. From the results of thermodynamic modeling of the equilibrium phase composition of the alloy, it was found that for the temperature range from 300 to 530°C, the presence of the β-phase (Mg2Si) is most likely. With the use of transmission electron microscopy and X-ray spectral microanalysis, it was found that during quenching, the decomposition of SSS leads to the precipitation of undesirable large particles of metastable β-type phases or equilibrium β-phase. The nucleation of the secretions is realized in the form of rod-shaped particles by a heterogeneous mechanism mainly on the surface of the α-phase dispersoids (Al15(Mn,Fe)3Si2), which thus significantly increase the quenching sensitivity of the alloy. The formation of these secretions at a low quenching rate causes, during subsequent aging, a decrease in the proportion and density of formation of strengthening particles of the β" phase, and also leads to an increase in their size and heterogeneity of distribution in the aluminum matrix, which reduces the potential of dispersion hardening during aging and corrosion resistance of the material.

In this paper the decomposition and evolution of microstructures of the metastable β-phase during aging of Ti10V2Fe3Al, VST5553, and Beta-21S alloys were studied. A comparative study of the evolution of the microstructure and crystal lattice of phases in alloys during aging has been carried out. Features of the nucleation and growth of the secondary α-phase formed during aging were observed using scanning electron microscopy. The concomitant diffusion redistribution of alloying elements between the phases was studied using the method of full-profile X-ray diffraction analysis. It has been established that during aging, the change in the periods of crystal lattices in the studied alloys has a general pattern, which is associated with the common nature of the process of diffusion redistribution of alloying elements between phases. The morphology formed during the decomposition of the secondary α-phase differs between alloys and is determined by the stability of the β-phase after quenching.

The biomedical alloy Ti-18Zr-15Nb (at.%) with shape memory was subjected to a true deformation e = 0.7 in three different modes: in the temperature range from 20°C to 600°C at deformation rate ξ = 0. 1 s-1; at temperatures 250°C and 300°C with strain rates ξ = 0.1, 1 and 10 s-1; deformation at 300°C and strain rate ξ = 0.1 s-1 after annealing at 300°C (τ = 10, 60, 300, 600 and 1200 s). It is established that with increasing temperature the conditional yield strength σ0.2 continuously decreases, at that in the temperature range of deformation temperatures 250°С-300°С the increase of maximum stress σmax is observed. In the temperature range from 200°С to 400°С fluctuations are observed on the flow curves, the amplitude of which increases with increasing temperature. The change σ0.2 and σmax, as well as the presence of oscillations on the strain diagrams are connected with the course of dynamic strain aging accompanied by the release of excess ω-phase particles at temperatures 200°С - 400°С. Increasing the strain rate at temperatures of 250°С - 300°С has a strong effect on the deformation behavior of the alloy due to a significant increase in temperature during the deformation process. Thus, increasing the strain rate up to ξ = 10 s-1 leads to a stepwise decrease in stress, starting from e ≈ 0.3, after which the plastic flow curve acquires a wave-like form with a low frequency of stress fluctuations. The main phase after all modes of thermomechanical tests is the BCC β-phase. At annealing of 300°С and an exposure of more than 300 s weak ω-phase lines are observed, and at deformation after aging significantly broadened ω-phase lines are observed only after prolonged exposure (1200 s).