Russian Physics Journal最新文献

Molecular dynamics study of the influence of phase distribution on the response of two-phase nanocrystalline Fe₉₅Ni₀₅ samples with a gradient grained structure under shock loading was carried out. It was shown that the propagation of a shock wave causes direct and reverse FCC-BCC-FCC phase transformations in grains with the FCC structure, BCC-FCC/HCP phase transformations in lamellas with the BCC structure, as well as the nucleation of the HCP phase. The shock wave and the wave reflected from the rear surface initiated transformation of a significant part of the sample into the HCP phase. Shock wave propagation in the sample caused the appearance of two maxima on the curve of the time dependence of the HCP phase volume fraction. Time changes in the HCP phase fraction correlated with changes in the fraction of atoms belonging to intrinsic stacking faults and the dislocation density in the FCC phase. A large volume fraction of the intrinsic stacking faults, a higher dislocation density, and a lower volume fraction of the HCP phase were observed in the case of the sample with BCC lamellas only in one layer of grains compared to the sample with BCC lamellas in all grains under shock loading.

The preparation of di-calcium magnesium silicate Ca₂MgSi₂O₇ doped with 0.5, 1.0, 1.5, 2.0 and 2.5 mol.% of erbium (III) using a solid state reaction method is reported. An X-ray diffraction pattern obtained from the sample at optimum photoluminescence (PL) emission intensity exhibits a quite prominent resemblance with the crystallographic open database (COD) with entry 96-900-6449. This confirms the valid preparation of tetragonal akermanite with a P-4 21 m (113) space group. A 980 nm laser source is used as an excitation radiation for recording the PL emission spectra. The emission spectra exhibit two distinguished prominent peaks centered at 534 and 623 nm. These peaks are attributed to the ²H_11/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of erbium (III) ions respectively. The sample with 2.0 mol.% of erbium (III) exhibits an optimum PL intensity, and beyond this the concentration quenching occurs. The thermoluminescence studies of the same sample suggest an existence of the near second order kinetics. Therefore, the sample could be a very good candidate in LED applications.

The ability to fabricate Ti–3Al–4V–9Fe/TiC metal matrix composites using the wire-feed electron beam additive technology is demonstrated. Ti–6Al–4V titanium alloy rods surface saturated with carbon are used as the feedstock. The microstructure and phase composition of the Ti–6Al–4V rods subjected to carburization and as-built Ti–3Al–4V–9Fe/TiC composites are studied using optical and scanning electron microscopy, as well as X-ray diffraction analysis. The concentration of alloying elements in the feedstock and the composite is measured by the energy-dispersive analysis. Different patterns of TiC particle distribution within β grains of 3D printed Ti–3Al–4V–9Fe/TiC composite and along their boundaries are demonstrated. It is shown that the formation of equiaxed β grains and carbide (TiC) and intermetallic (TiFe) phases results in a high microhardness of the 3D printed Ti–3Al–4V–9Fe/TiC composite of 7 GPa.

Effect of microalloying by boron, added by two different methods, on the microstructure and martensitic transformation in as-cast and aged Ni₅₄Fe₁₉Ga₂₇ alloys was studied. The increase of the aging time of the Ni₅₄Fe₁₉Ga₂₇ alloy from 0.5 to 10 h at 823 K leads to the formation of a large volume fraction of the ordered γ′-phase. Microalloying with boron inhibits the precipitation of the γ(γ')-phase and prevents its ordering. The parameters of martensitic transformation are most stable with increasing aging time of a (Ni₅₄Fe₁₉Ga₂₇)_99.7B_0.3 alloy when boron is added in the form of a NiB alloy.

In this work, the structure of a CrMnFeCoNiCu high-entropy alloy (HEA) film deposited by magnetron evaporation on a steel substrate is studied. It is established that the phase content of the CrMnFeCoNiCu HEAs is determined by a superposition of contributions from equiatomic simple cubic lattices of the CrMnFeCoNiCu composition (Struct-26 and Struct-278) with space group P1. It is found that the contributions of the diffraction patterns from the reference lattices to the integral intensity are 0.66 and 0.29, respectively. For simple cubic lattices Struct-26 and Struct-278, the full structural information (the lattice parameters, coordinates of atoms, spatial groups, and occupancies) is derived. It is established that the CrMnFeCoNiCu HEA is a stable compound, which is confirmed by calculations of the mixing energy for the convex Hull model.

Modern conditions of mineral deposit development are characterized by more stringent requirements as to the environmental impacts of production and the increased volume of blasting operations near populated areas. The importance of the study is due to the need of developing energy-efficient technologies for crushing rocks, finding safe ways to intensify the coal degassing processes and reducing the intensity of methane inflow into the mined-out space. The Smoothed Particle Hydrodynamics numerical method used in this work allows adequately calculating nonlinear dynamic problems arising during blasting development of mineral deposits, while the use of most other computer modeling methods to solve these problems causes significant computational difficulties. The paper presents the results of a study of the nature of variations in the rock displacement velocity and the stresses and parameters of the radial crack propagation zone from the distance to the charge during blasting operations in monolithic and fractured massifs.

Cylindrical samples made of siliconized graphite SG-P0.5 are experimentally studied in a wide range of strain rates (10^-4 to 10³ 1/s). Quasi-static and dynamic loading is performed under conditions of fragment preservation. Quasi-static compression is applied and acoustic emission signals are recorded in situ. The data processing and the analysis of the fragmentation statistics show the destruction of siliconized graphite under the loading conditions.

Molecular dynamics (MD) is a powerful tool for modeling the phase and structural transformations and the evolution of defects and their influence on the metallic material properties. The accuracy of MD modeling directly depends on the quality of interatomic potentials. Modern machine-learning potentials are typically trained on random atomic configurations. This approach has significantly improved the quality of new potentials over traditional EAM potentials. In this work, exact solutions to the equations of atomic motion are offered to train the machine learning potentials.

The paper studies the alloying effect of the quenched Ni-low (Ni_49.5Ti_35.5Hf₁₅)_100–XNb_X and Ni-rich (Ni_50.3Ti_34.7Hf₁₅)_100–XNb_X alloys (X = 0, 15 at.% Nb) on the B2-B19' martensitic transformation, viscoelastic properties and microstructure. Alloying of Ni-low and -rich alloys with Nb, provides the β-Nb phase precipitation within the (Ti, Hf)₂Ni phase. After alloying, the transformation temperature and austenite elastic modulus decrease in Ni-low alloys and increase in Ni-rich alloys, thus making them similar.

The two-way shape memory effect with reversible compressive strain up to 5.1% and high cyclic stability is obtained for Ni₄₄Fe₁₉Ga₂₇Co₁₀ (at.%) single crystals by stress-induced martensite aging at 398 K for 1–3 h, under 650 MPa. 100 cycles of thermal treatment at temperatures not exceeding aging temperature, do not affect the temperature of the martensite formation, and reversible strain reduces merely by 0.4%. Thermal cycling with aging overheating significantly decreases reversible strain down to 1% due to the austenite stabilization.