Том 125, № 9 (2024)

The phase composition of the Al–Cu–Ca–Mn alloys containing (wt %) 6% Cu, 2% Mn, and to 4% Ca is analyzed. The Al–Cu–Ca–Mn phase diagram in the Al corner is proposed, according to which five four-phase regions with the participation of Al-based solid solution (Al) and various intermetallic compounds are possible to exist in the solid state. The Al–6% Cu–1% Ca–2% Mn composition is suggested as the base for developing new-generation heat-resistant (hot-strength) alloys. In the case of such contents of alloying elements, the combination of aluminum matrix containing Al₂₀Cu₂Mn₃ dispersoids and (Al) + Al₂₇Ca₃Cu₇ eutectic characterized by fine structure is possible.

The thermal stability of single-phase Ni–Cr alloys (with 2, 5, and 12.5 at % Cr), in which the submicrocrystalline (SMC) structure is formed by high-pressure torsion, is studied. Annealing-induced variations of the hardness and grain size, and changing the uniformity of recrystallized structure are analyzed. The alloying of nickel with chromium increases the temperature of the onset of recrystallization of deformed alloy by 150–250°С and temperature of the onset of active grain growth by 200–400°С in accordance with the increase in the chromium content. The recrystallization of the studied SMC alloys develops via the priority growth of individual nuclei. The increase in the chromium content in the alloys from 2 to 12.5% favors the decrease in the grain size and increase in the size uniformity of the recrystallized structure.

Molecular dynamics (MD) simulations were applied to study primary damage formation in a Fe–Ni–Cr ternary model alloy with chemical composition that coincides with Fe, Ni, and Cr content in AISI type 304 stainless steel. A representative sample of 12 960 radiation damage formation events initiated by Fe, Ni, and Cr primary knock-on atoms (PKA) with PKA energy 100 eV ≤E_PKA≤ 5 keV along fifteen crystallographic directions is employed for evaluation of the average threshold displacement energies. It is established that the average threshold displacement energies of Fe, Ni, and Cr atoms in the considered material are identical and equal to ⟨E_d⟩=28±1 eV. As a function of E_PKA, the actual average threshold displacement energy E_d comprises of two linear segments that depend on the governing mechanism of primary damage formation. PKAs with energies E_PKA≤E_cc, where E_cc≈0.8 keV, generate isolated vacancies and interstitial atoms, whereas PKAs with energies E_PKA≥E_cc produce radiation damage in collision cascades. Using the obtained results of MD simulations, we modified the cascade function in the Kinchin-Pease model in order to take into account the dependence of the actual threshold displacement energy E_d on PKA energy E_PKA.

The time-temperature changes of martensite lattice parameters (MLPs) of Ti–50.26Ni and Ti–18Zr–14Nb (at%) shape memory alloys have been investigated using X-ray diffraction methods both in situ and ex situ in order to verify the existence of the time dependence of MLPs and to ascertain the extent to which the correct syngony of the martensite lattice is preserved when its parameters change during heating and cooling at temperatures ranging from –180°C to ≥ As. The reversibility of MLP alterations was observed across the entirety of the investigated temperature range, when subjected to disparate combinations of heating and cooling rates (ranging from 0.03 to > 50°C/s). The MLP values remain constant regardless of the duration of X-ray diffraction imaging or holding at a given temperature within the martensite existence interval. The width of the X-ray lines of B19′ and α″ martensite remains constant regardless of the heating and cooling rates and holding times, which suggests the absence of martensite lattice distortions akin to those observed in premartensitic materials, leading to reversible broadening of X-ray lines of austenite with approaching the Мs point in the area of formation of nanodomains of intermediate shear structure. The Fisher criterion (F), nowhere exceeding its critical value, in conjunction with the unaltered width of the X-ray lines, suggests that the undistorted lattice syngony of unconverted martensite crystals has been preserved and that the lattice as a whole has undergone gradual homogeneous shear as the reverse transformation was approached.

Using complex theoretical and experimental methods of analysis, the influence of diffusion and deformation processes on the chemical composition and structure of the welded joint of plates made of D16T aluminum alloy under friction stir welding conditions was assessed. To reproduce the temperature conditions in the welding zone and assess the possible causes of changes in the structure and phase composition of the material in the weld area, methods of mathematical modeling of thermal processes were used. The resulting theoretical calculations were tested and confirmed using experimental methods of structural analysis (X-ray structural analysis and scanning electron microscopy) and microhardness measurements. A change in the content of silicon, copper and aluminum in the composition of the solid solution of the material under study was detected, as well as a change in the phase composition (a decrease in the amount of the Al₁₂Fe₃Si phase and the appearance of the AlCuFeMnSi phase), which is associated with mass transfer in the zone of the welded joint under friction stir welding conditions.

For one-dimensional case of binary substitution alloys, the parameters of the diffuse interface and the distribution of the composition within it are calculated using the thermodynamic approach. It is shown that the estimate of the equilibrium solubility limits in the quasi-regular solution model coincides with the results of the Gibbs construction and the results obtained using the Cahn–Hilliard approach. It is found that the interface width weakly depends on the chosen approximation. A strong dependence on the employed approximation is characteristic of the equilibrium solubility limits. It is also demonstrated that approaches that are different from the quasi-regular solution model lead to a violation of Maxwell’s equal area rule. It is shown that the parameters determining the shape of the distribution curve of the composition along the interface have substantially different behavior within the quasi-regular solution model and in the case of regular calculations.

The change in the structure and hardness of the Fe–Ni–Ti–C–B system composite, obtained by the method of self-propagating high-temperature synthesis (SHS), after hot plastic deformation under uniaxial compression conditions has been studied. The matrix of the composite is a solid solution of Ni and Ti in a γ-Fe crystal lattice, strengthening phases are TiC, TiB₂, Fe₂B, Ni₃Ti and NiTi. It is shown that during uniaxial compression upon heating, recrystallization processes occur in the metal matrix of the composite, which facilitate further deformation. It is found that, after compression at a temperature of 910°C and a pressure of 300 MPa, the true deformation of the composite is 0.37. In this case, in the central part of the sample in the region of compressive stresses, the ratio of deformed and recrystallized grains is approximately the same. On the lateral surface of the samples in the zone of action of tensile stresses, microcracks with a depth of less than 0.2 mm appear in zones of the eutectic γ + Fe₂B structure.