Physical Mesomechanics最新文献

In hydraulic barriers and waste disposal sites, sand and bentonite mixtures are often used as backfill or liners. This research focuses on the importance of understanding how to safely store radioactive and solid waste long–term. This is the first study in the literature to explore how temperature affects damage in sand–bentonite mixtures using fracture mechanics. The findings revealed that more bentonite increases sensitivity to temperature, reduces cohesion, and increases internal friction. Moreover, results showed that higher temperatures and bentonite content decreased fracture toughness and created significant damage zones at crack tips. Scanning electron microscopy and interactive 3D images showed that shear damage mainly facilitates the sliding and rolling of coarser grains at high temperatures, leading to particle alignment along failure planes. Non–linear numerical analyses with a cohesive zone model revealed that the greatest traction opening and sliding in the cohesive crack occurred at 80 and 25°C for the 30B-70S specimens. The relationships between fracture toughness and common soil mechanical properties at the investigated temperatures were also investigated. The fracture toughness test results showed that increasing temperature and bentonite content reduced the fracture toughness of the 10B-90S samples by 30% at room temperature and by 30% at 80°C.

High-entropy alloy (HEA) coatings based on the Cr–Ti–Zr–Nb–Hf system represent a promising class of functional materials intended for application under extreme operation conditions. This study presents a comprehensive investigation of Cr–Ti–Zr–Nb–Hf HEA coatings, both in their as–deposited state and following nitrogen modification. Ion–plasma sputtering of the coatings was conducted in Ar and Ar + N₂ atmospheres, respectively. Synchrotron X–ray absorption spectroscopy (XAS) revealed that nitrogen incorporation facilitates the formation of a single–phase high–entropy nitride, designated (Cr, Ti, Zr, Nb, Hf)N, characterized by strong covalent metal–nitrogen bonds and substantial lattice distortion. Nitrogen modification was found to yield more than a twofold increase in hardness and an approximately twofold increase in Young’s modulus in contrast to nitrogen–free sputtering. Tribological tests conducted over a temperature range of –60°C to +150°C demonstrated high thermal stability of the nitride coating. Nitrogen–assisted modification further enhanced wear resistance by nearly an order of magnitude, while the coefficient of friction decreased by a factor of three to four. A model–based description of the structural and mechanical characteristics employing the Miedema model and the Mazhnik–Oganov framework along with an analysis of tribological properties grounded in the Bowden–Tabor and Archard theories, exhibited good agreement with experimental observations. The findings of the study indicate that the (Cr, Ti, Zr, Nb, Hf)N coating represents a stable, high–strength high–entropy compound dominated by covalent interatomic interactions.

The effect of Ca addition (up to ~3.5 wt.%) on the structure, phase composition, deformability and mechanical properties of hot and cold rolled aluminum alloys containing 5–6%Cu and ~2%Mn alloys has been studied using calculation and experimental techniques. It has been shown that the main structural component of the most promising (wt.%) Al–6Cu–1Ca–2Mn alloy is the eutectic (Al)+Al₂₇Ca₃Cu₇, which has a fine structure and contains (wt.%) ~5.8 Cu, ~1.6 Ca and ~2 Mn. Increasing the Ca content to more than 1 % leads to a decrease in the alloy processability due to the formation of primary crystals of the Al₂₇Ca₃Cu₇ phase. It has been shown that combining the eutectic phase Al₂₇Ca₃Cu₇ crystals in an amount of ~8% and Al₂₀Cu₂Mn₃ phase dispersoids in the Al–6%Cu–1%Ca–2%Mn alloy delivers a significant increase in the strength of the cold-rolled sheets annealed at 400°C (UTS 319 MPa, YS 269 MPa and δ 8.4 %). Based on the data obtained, the Al–6%Cu–2%Mn–1%Ca composition offers the best combination of deformation processability and mechanical properties. Therefore, it can be considered as a basis for developing new generation heat-resistant wrought aluminum alloys.

A novel heat-treatable wrought alloy (wt. %): Al–5.6Cu–0.35Ca–0.51Mn–0.29Zr was cast as a 20 mm thick flat ingot, followed by homogenization annealing and hot rolling at 450 °C to a final thickness of 2 mm. Scanning electron microscopy (SEM) confirmed that the copper solubility in the aluminum matrix reached ~5.1 wt. %, satisfying the requirements for a pronounced precipitation hardening effect. Aging at 175 °C revealed a peak hardness of 145–150 HV achieved within ~4 h, which is comparable to the commercial 2219 alloy. Transmission electron microscopy (TEM) data suggest that the hardening is due to the formation of ultrafine coherent θʹʹ phase precipitates. Intergranular corrosion (IGC) tests showed that the new alloy performs similarly to the commercial AK4–1 alloy, with a mass loss of ~2 % after 24 h and a corrosion depth of 150–200 µm. Uniaxial tensile testing after corrosive exposure revealed a 20 % reduction in tensile strength for both alloys. Notably, the fracture mechanism in the corrosion-affected zones shifted from ductile transgranular dimpled fracture to brittle intergranular mode

This study systematically investigates the influence of the non-metallic component type (X = N, C, CN) and deposition parameters (temperature, bias potential) on the structure, mechanical properties, and high-temperature oxidation resistance of multicomponent (AlCrNbSiTi)X coatings. The coatings were synthesized by reactive magnetron sputtering and characterized using SEM, XRD, instrumented indentation testing, and TGA (1300 °C). It was established that (AlCrNbSiTi)N nitride coatings surpass their carbide and carbonitride counterparts in both hardness (up to 47 GPa) and oxidation resistance. The bias potential was identified as a key factor determining the oxidation mechanism; a -40 V bias initiates a transition from through-thickness oxidation to protective passivation by forming a dense oxide layer. Furthermore, the optimal condition (no heating, -40 V) creates a nanostructure (25 nm crystallite size), enabling a synergy of ultra-high hardness and maximum oxidation resistance due to rapid Al and Cr diffusion. These results demonstrate the potential for purposefully controlling the high-temperature performance and mechanical properties of multicomponent nitride coatings by managing ion bombardment and microstructure.

This study investigates the macrostructure, microstructure, and mechanical properties of near-net-shape gas turbine Ti–6Al–4V blade models manufactured via wire electron beam additive manufacturing (WEBAM) using different spatial profile rotation angles (10°, 20°, and 30°). A comprehensive study using optical and scanning electron microscopy, as well as backscattered electron diffraction, showed that dense metal is formed with a pronounced columnar prior β–Ti grain boundaries and lamellar Widmanstätten α–Ti microstructures. It has been established that there is a gradient in the structural–phase state along the height of the part: from α'–Ti martensitic structures in the upper layers to coarse α / β lamellar colonies in the lower layers, which have undergone multiple thermal cycling. It has been found that the profile rotation angle significantly affects the heat dissipation kinetics and crystallography: the minimum angle (10°) leads to strong anisotropy, the maximum (30°) promotes the refinement of α–Ti colonies and the formation of a chaotic texture with a high proportion of high–angle boundaries, while a 20° rotation provides the most balanced and homogeneous structure. Mechanical tensile tests for all products demonstrated a decrease in yield strength from the lower layers to the upper ones. At the same time, the product with a 20° twist angle showed the best uniformity of properties throughout its volume. An important practical result of the work is the experimental proof of the representativeness of standard model samples for predicting the properties of complex–shaped aviation products, which opens up prospects for the implementation of WEBAM technology in the production of gas turbine blades.

A microstructural model of the monoclinic M_A phase of a ferroelectroelastic material is proposed. The polarization direction occupies an intermediate position between the polarization directions of the tetragonal <001> and rhombohedral <111> phases. The fully coupled electromechanical microstructural model takes into account the multidomain structure, the dissipative domain wall motion, and the inhomogeneous distribution of mechanical stress fields and electric field strength in crystallites. The material response at the macrolevel is obtained by finite element homogenization of a representative volume element of polycrystalline piezoceramics. The proposed microstructural model allows to predict the extreme properties (high values of spontaneous polarization and spontaneous strain) of polycrystalline piezoceramics at the morphotropic phase boundary. Comparison of dielectric and electromechanical hysteresis curves demonstrated good prediction accuracy for experimentally observed curves for polycrystalline piezoelectric ceramics PZT PIC151.

Non–equiatomic Nb–Co–Cr–Ni–Mn medium–entropy alloys were designed based on thermodynamic modeling to achieve solid solution strengthening while maintaining a stable FCC structure. Five compositions (Nb₂Co₄₀Cr_26–12Ni_30–40Mn_2–6) were fabricated by arc melting and characterized using XRD, SEM–EDS, TEM, and nanoindentation. XRD confirmed FCC crystal structures in all alloys, though peak broadening suggested potential phase complexity. SEM–EDS revealed dendritic microstructures with systematic Nb segregation to interdendritic regions (4.9–7.9 at. %) and Nb–rich intermetallic phases in two compositions. Molecular dynamics simulations using the PET–MAD potential predicted Nb–Mn short–range ordering. Nanoindentation measurements showed hardness values of 112–142 HV₁, comparable to the baseline CoCrNi alloy. The results indicate that while non–equiatomic compositions can enhance Nb solubility compared to equiatomic alloys, solidification segregation and secondary phase formation remain challenges requiring homogenization treatment.

Due to the severe plastic deformation introduced into the parent material during friction–stir processing (FSP), the original microstructure is often substantially replaced. As a result, it is sometimes believed that the FSP–processed microstructure is largely independent of the initial material state. While this assumption holds true for non-heat-treatable aluminium alloys, this study challenges its universality for heat–treatable alloys. Using the 2519 Al–Cu–Mg alloy as a model system, it is demonstrated that а transitioning from the initial hot–rolled state to solution–treated (W) and aged (T6) temper conditions significantly reduces the processing temperature under identical FSP parameters. This leads to substantial changes in the resulting microstructure, particularly in the precipitation pattern, thereby exerting a pronounced effect on the mechanical performance and annealing behaviour of the FSP–processed materials. It is deduced that this phenomenon was associated, at least partially, with the variations in thermal conductivity caused by differences in solute content within the aluminium matrix.

The creation of structural and functional materials based on corundum ceramics with high physical and mechanical properties is an urgent task of modern science and technology. In this regard, new methods for producing ceramics are being searched for, including those using nanodispersed components. In this work, the effect of modifying additives obtained by electric explosion of wires in a mixture of Ar and O₂ on characteristics of sintered Al₂O₃ nanopowder was assessed for the first time. The conducted complex of studies showed that the introduction of 3 vol. % modifying additives in the form of CuO, TiO₂, Fe₂O₃ nanopowders and compositions based on them significantly increases the relative density of the sintered compact. This is attributed to the lower homologous temperature of the modifiers relative to the matrix and to the formation of novel, less refractory ionic compounds. It was found that differences in the coefficients of thermal expansion of the matrix and modifying oxides lead to relaxation, or a noticeable increase in the second-order stresses in the matrix. At the same time, the observed strengthening of the sintered composites, compared to unmodified Al₂O₃, is apparently due to the increased relative density rather than to residual compressive stresses that have a dissipative effect on cracks propagating in the ceramics.