Phase composition, microstructure, and microhardness of the surface layers formed in high-entropy Cantor alloy (CoCrFeMnNi) specimens during ion-plasma nitrogen saturation at temperatures of 400°C, 450°C, 500°C, 550°C and 600°C (for 1 hour) have been studied. Ion-plasma nitriding leads to the formation of a composite surface layer consisting of nitrogen-supersaturated austenite (FCC’-phase), which partially decomposes to form the FCC(FCC’) phase and CrN nitrides. Increasing the saturation temperature assists more complete transformation of the nitrogen supersaturated FCC phase, and composite layers up to 26 micrometers in thickness are formed after treatment at 550–600°C. The thickness of the modified surface layer monotonically increases with increasing treatment temperature up to T = 500°C, after which it reaches saturation regime. It has been shown that nitriding enhances the surface hardness of the specimens. The highest microhardness values, up to 20 GPa, are characteristic of structural states where a mixture of nitrogen-supersaturated austenite and dispersed chromium nitrides are formed.
High–entropy alloys (HEAs) are alloys consisting of five or more components in an equiatomic (or close to it) ratio. They are promising materials for operation in extreme conditions due to a unique combination of various properties. HEAs alloyed with Nb demonstrate an optimal combination of mechanical and tribological properties, which makes these alloys interesting for use in a number of industries, including the production of gas turbines and turbojet engines. However, the behavior of niobium–containing HEAs at high operating temperatures has not been sufficiently studied yet. This work aims to investigate the high–temperature oxidation resistance behavior (at 1000 and 1100°C) of as–cast Al0.5CoCrNiNb0.5 HEA. The effect of long–term holding (100 h) at high temperatures on the microstructure and microhardness of the alloy is studied. Moreover, the effect of niobium on the morphology, phase, and chemical compositions of the formed oxide film was examined, and other oxidation parameters (specific mass gain, oxidation rate constant, and activation energy) were identified. It was observed that niobium takes part in high–temperature gas corrosion process with the formation of oxide compounds such as Nb2O5, AlNbO4, CrNbO4; however, aluminum and chromium oxides, CoCr2O4 and NiCr2O4 spinels are the main components of the formed film on the surface. In general, the studied HEA demonstrates fairly good resistance to high–temperature oxidation. The maximum specific mass gain after 100 h isothermal holding in air at 1000°C was 0.818 mg/cm2, and after holding at 1100°C this value was equal to 1.363 mg/cm2.
Phenomenological and physically based constitutive models were developed using true stress–true strain curves obtained through hot compressing test of Ti–5Al–4Mo–6V–2Nb–1Fe alloy. The experimental data acquired under the different temperatures (700, 800, 900, 1000 and 1100°C) and strain rates (0.001, 0.01, 0.1, 1 and 10 s–1) conditions were modified considering friction. Based on the modified experimental data, the modified Johnson–Cook model, Arrhenius type model (phenomenological models) and the microstructure–based model (a physically based model) were developed to predict the hot flow stress of the alloy. And for each model, the average absolute relative error and determination coefficient were evaluated by comparing the experimental data to the predicted stress value. The determination coefficients were 0.9937, 0.9949 and 0.9956 for the modified Johnson–Cook model, Arrhenius type model and microstructure–based model, respectively. And the average absolute relative errors were respectively 6.71, 5.59 and 3.57
Laser powder bed fusion (L-PBF) is a type of additive manufacturing (AM) technology that offers the ability to produce complex-shaped products with high accuracy. To effectively control properties of the AM products, a thorough understanding of the underlying metallurgical phenomena is necessary. In this sense, precipitation-hardened martensitic steels may serve as an excellent model material for such a study, as they experience both a series of solid-state phase transformations and precipitation phenomena during L-PBF. This work provides a critical overview of the scientific literature on L-PBF of typical 17-4 PH precipitation-hardened martensitic steel. Particular attention was given to the key issues of the L-PBF process, including (a) powder atomization, (b) principal variables and evaluation of their optimal combination, (c) volumetric defects, phase composition, microstructure and mechanical properties of AM parts, and (d) post-processing heat treatment.
In this work, the effect of Gd alloying on the microstructure, α-grain growth kinetics, and recrystallization processes in the single–phase α-phase field was investigated using two alloys based on gamma titanium aluminide Ti-47.1Al-1.8Nb-0.5Zr-0.3V-0.001Gd (0.001Gd) and Ti-46.9Al-1.6Nb-0.5Zr-0.5V-0.03Gd (0.03Gd). It was shown that an increase in the Gd content from 0.001 at.
This paper reports on the elastoplastic properties of additively manufactured specimens made of metamaterials based on the biocompatible titanium alloy Ti6Al4V, known as meta–biomaterials. The paper presents the results of experimental tests for three types of meta–biomaterials composed of beam–based Diamond unit cell and surface–based Gyroid and IWP unit cells, with 30, 50 and 70
In this work, a layered composite material was obtained by the method of free SHS compression, which combines the processes of self-propagating high-temperature synthesis and high-temperature shear deformation, using initial powder components of titanium, boron, and aluminum, as well as a VT1-0 titanium substrate. It is shown that the resulting composite consists of a TiB-based ceramic layer, a Ti-Al-based intermetallic layer, and an α-Ti titanium layer, with the interfaces between them having a wavy and diffuse character. The influence of high-temperature annealing in an oxidizing atmosphere at a temperature of 1000°C for 1 h on the structure, phase composition, and mechanical properties of each layer in the obtained composite was determined. The results of SEM, powder X-ray diffraction, and EDS analysis of the studied layered composite materials before and after annealing are presented. It was found that during annealing, the intermetallic layer, which initially consists primarily of the TiAl3 phase, undergoes transformation into the main phases TiAl and Ti3Al due to diffusion processes, while free titanium reacts with nitrogen to form up to 10 wt.
The multiscale elastic response of stainless steel 316L fabricated by laser powder bed fusion has been investigated using a combination of grain-resolved finite-element simulations and analytical Voigt–Reuss–Hill homogenization based on experimentally measured crystallographic texture. Grain structures and orientations have been reconstructed directly from electron backscatter diffraction data obtained for the top and lateral planes of the printed material. The simulations have been used to analyze the development of local stress–strain fields under uniaxial loading along the scanning, build, and transverse directions, while the analytical approach has been employed to reconstruct the directional dependence of the effective elastic properties in three-dimensional space. The results have demonstrated that the characteristic layered grain morphology formed during laser powder bed fusion, consisting of alternating cube- and Goss-oriented grain regions, produces pronounced anisotropy of the elastic response. The effective Young’s modulus has been found to be significantly lower along the scanning direction than along the build and transverse directions due to the prevailing crystallographic texture. At the grain scale, periodic sandwich-like stress distributions have been observed, arising from the spatial arrangement of grains with different elastic stiffness and anisotropic transverse deformation behavior. The simulations have shown that loading parallel to the grain layers is governed mainly by directional elastic stiffness, whereas loading across the layers generates substantial transverse stresses associated with strain-compatibility constraints between neighboring grains. The analytically predicted elastic moduli have shown close agreement with the finite-element results and available experimental data, confirming the predictive capability of both approaches. It has been demonstrated that grain-resolved simulations and analytical homogenization provide complementary insight into the elastic behavior of additively manufactured materials by linking local microstructural characteristics with macroscopic anisotropic properties.
Functionally graded sandwich spherical shallow nanoshells are widely used in advanced microsystems due to their tunable material behavior and superior stiffness-to-weight ratio. Conventional nonlocal elasticity models often assume a constant nonlocal parameter through the thickness, which may be inaccurate for graded materials. This study investigates the free vibration behavior of such nanoshells using a modified nonlocal elasticity theory where the nonlocal parameter varies continuously along the thickness. The governing equations are derived using higher–order shear deformation theory and Hamilton’s principle and solved analytically via Navier’s method for simply supported boundaries. Results show that increasing the nonlocal parameter significantly reduces natural frequencies, with softcore configurations being more sensitive than hardcore ones. The vibration response is also affected by the material gradient index, layer thickness ratios, and shell geometry. The proposed model captures size–dependent effects more accurately and offers improved prediction of nanoscale behavior. These findings provide useful guidance for the vibration–based design of graded nanostructures and can be extended to incorporate thermal or damping effects in future studies.
The study of mechanical properties and thickness of the interphase in polymer-matrix composites is necessary for a deep understanding of the strength and reliability of the composite material. The interphase is an intermediate layer between different phases, has a significant effect on the stress distribution inside the material and, as a result, affects the mechanical and operational characteristics of the composite. The selection of the interphase parameters can improve the elastic, strength and fatigue properties of the composite. The purpose of this work is to investigate the influence of external curing pressure on the formation of interphase thickness and its elastic properties in a fiberglass plastic composite. Based on data obtained using dynamic force microscopy, experiments demonstrate that increasing external curing pressure from 0 to 10 MPa leads to a decrease in interphase thickness from 1232 ± 95 nm to 212 ± 71 nm, and this decrease is described by an exponential dependence. The computational mesomechanical model of the composite monolayer shows that increasing pressure from 0 to 2 MPa increases the elastic modulus of the interphase from 6.3 GPa to 7.9 GPa. At the same time, external pressure does not affect the Poisson’s ratio of the interphase, which remains in the range of 0.18–0.20. The Poisson’s ratio of the monolayer does not change with increasing external curing pressure and constitutes 0.24 ± 0.02, which is related to a compensatory effect caused by redistribution of volume fractions of structural components: an increase in the fiber fraction with low Poisson’s ratio (0.23) and a decrease in the matrix fraction with high Poisson’s ratio (0.33) are compensated by changes in the contribution of the interphase. The study also shows that the elastic modulus of the interphase exceeds the elastic modulus of the matrix, while the Poisson’s ratio is lower. In addition, the work determines the elastic modulus and Poisson’s ratio of single glass fibers based on micromechanical tests.
This study proposes an efficient method for numerical modeling the failure mechanisms in nickel-based alloy XH73M within the phase-field approach. The material’s microstructure was approximated using a Voronoi diagram, which allowed for accounting the influence of the grain structure on crack initiation kinetics. Critical values of the energy release rate for the nickel alloy are proposed for conditions at 20°C, 400°C, and 650°C. A comparative analysis of crack growth kinetics under monotonic static and cyclic loading was performed. It was found that under identical conditions, multiple crack branching occurs under static loading, whereas under cyclic loading, crack propagation develops in a more orderly manner. The analysis of crack growth rates at 20°C, 400°C, and 650°C revealed that when intergranular fracture dominates, localized crack retardation zones are observed, associated with the need to bypass grains along their boundaries. The total potential energy and its components (strain energy density, accumulated volumetric energy, fracture energy) were evaluated as functions of the damage parameter φ within degraded elements.
The paper considers the rheological properties and structure formation of the new bioresorbable Zn-0.8Li alloy subjected to uniaxial compression at different initial temperature–velocity conditions and equal-channel angular pressing (ECAP). The rheological properties are investigated based on the results of the compression tests of cylindrical specimens at temperatures from 100 to 300°C and a strain rate of 1.6 s−1. It has been found that at Ti = 100°C, the flow stress-strain curve of Zn-0.8Li is cyclical: first, the material hardens, then softens, and then hardens again. At Ti = 200°C, the flow stress-strain curve exhibits a horizontal section instead of a descending branch, followed by hardening. The maximum deformation–induced heating is observed at Ti = 100°C and reaches a value of 70°C. The lowest amount of dissipated energy is observed at Ti = 300°C. Structural analysis shows that at Ti = 100°C the regions of primary dendrites are plastically deformed, while the eutectic regions are more susceptible to mechanical fracture. An effective refinement of both phase regions occurs at temperatures above 300°C due to dynamic recrystallization. The average grain size in both areas reaches 4–5 μm. Based on the obtained data on the rheological behavior of the Zn-0.8Li alloy, a regime was selected and ECAP processing was performed at Ti = 300°C. Structural analysis of the obtained samples indicates refinement of the phases due to dynamic recrystallization. In the case of the eutectic region, the bulk of the grains is of recrystallization origin, and in the regions of primary dendrites, low–angle boundaries are formed and internal stresses accumulate. Due to an increase in the length of the intergrain boundaries, the ductility parameters increase by 7.5 times—the tensile elongation reaches 30
This study investigates adsorption–induced resonance shifts in biomolecule-microresonator systems, accounting for shear distortion, distributed adatoms, and small–scale influences. A dynamic model is formulated for a functionally graded porous (FGP) resonator with a hollow microbeam, integrating surface stress effects. The aim of this study is to develop a comprehensive model for the dynamic behavior of biomolecule–microresonator systems by incorporating multiple coupled effects, including van der Waals (vdW) interactions, magnetic fields, porosity, and perforation. The originality of the work lies in the integration of nonlocal elasticity theory with both Lennard–Jones and Morse potentials within a hollow functionally graded porous sandwich microbeam model, which has not been simultaneously addressed in previous studies. The analysis applies a functional sandwich microbeam framework and a localized biomolecule approach, incorporating van der Waals (vdW) interactions via Lennard–Jones (6–12) and Morse potentials to evaluate all influencing parameters. Adsorption–induced energy is represented through a distributional approach for both bio-receptors and spike proteins. The vibration equations are constructed using the Euler–Bernoulli beam model (EBM) and Levinson beam model (LBM), with solutions derived through the Navier solution method (NSM) and the differential quadrature method (DQM) to determine resonance frequency shifts. Numerical analysis reveals that the frequency shift response is dictated by perforation characteristics, adsorbed adatoms, magnetic field strength, and small–scale effects. Furthermore, the shift is influenced by active surface parameters, receptor-spike interactions, and adatom adsorption, with interatomic forces enhancing the flexibility of the sandwich microsystem. These findings emphasize the necessity of incorporating such interactions in computational models. The proposed approach effectively examines biomolecule–resonator dynamics and determines the mass and density of spikes and viruses in the presence of adatom bonds. Additionally, the study assesses the nonlocal dynamic behavior of adatom–microstructure systems, offering critical insights for refining mass sensing technologies in bio-microelectromechanical systems (Bio–MEMS).
Since 2012, intermetallic alloys based on the γ(TiAl) + α2(Ti3Al) phases have been used as a material for low–pressure turbine blades in gas turbine aircraft engines replacing conventional nickel–based superalloys. However, the use of these alloys remains limited. This is due not only to their inherent brittleness and low crack resistance, but also to insufficient creep and oxidation resistance at temperatures of 700–750°C and above. In the present work, novel physicochemical approaches to alloying intermetallic alloys based on γ(TiAl) + α2(Ti3Al) phases were proposed, followed by their practical implementation. According to the proposed approaches: i) the alloying elements should have high solubility in intermetallic phases; ii) it is preferable for the alloying elements to be refractory metals and have larger atomic radii than Ti and Al; iii) it is desirable that the alloying reduces the lattice misfits of the γ(TiAl) and α2(Ti3Al) phases; iv) it is preferable that the alloying does not lead to an increase in the content of the brittle α2(Ti3Al) phase and an increase in the tetragonal distortion of the γ(TiAl) phase; v) the difference in electronegativity of the alloying elements and the base elements (Ti and Al) should not be too significant. To achieve the goal, the alloys based on Ti–(43.5–44)Al (at.
Although hyperelastic models have been studied for almost 80 years, selecting one that accurately describes the mechanical response of materials remains a challenge. The most prominent examples of hyperelastic materials are biological tissues of living organisms. Information on models of hyperelastic biological materials is highly fragmented, typically focusing on specific individual models or particular organ tissues, and is published across various sources, with some applied aspects being insufficiently covered. This paper presents and analyzes the primary analytical formulations of the most common hyperelastic models (neo-Hookean, Mooney–Rivlin, Ogden, Polynomial, Yeoh, Veronda–Westmann) for calculating and analyzing the deformational behavior of materials. Consolidating essential information about these models in a single publication facilitates an informed choice of a model for computations and analysis of the deformation behavior of a hyperelastic material. Stress–strain curves, elastic modulus–strain curves, and statistical modeling parameters constructed based on the examined applied relationships are provided for the duodenum—the initial section of the human small intestine. Finally, formal approximating models: linear, bilinear, trilinear and exponential models of biological tissues are discussed as alternatives to hyperelastic models. The predictive capabilities of these standard analytical models are compared with those of their hyperelastic counterparts.
The double perovskite compounds Cs2AgBiX6 (X = Br, Cl) are promising lead–free alternatives to conventional halide perovskites. In this study, we employ first–principles calculations based on Density Functional Theory within the WIEN2k framework to investigate their structural, electronic, optical, and thermoelectric properties. The structural properties were analyzed through geometry optimization and stability assessment to ensure the most energetically favorable atomic configuration. Crystallographic parameters and structural stability factors were evaluated to understand their influence on mechanical robustness and phase stability. The electronic properties were studied using both the Generalized Gradient Approximation and the Modified Becke–Johnson approximation to compute the electronic structure and bandgap values. The results indicate that both compounds exhibit an indirect bandgap, with the Modified Becke–Johnson approximation providing more accurate bandgap estimations compared to the Generalized Gradient Approximation, making it more consistent with experimental values. Optical analysis revealed that Cs2AgBiCl6 exhibits a stronger optical response, making it a promising material for optoelectronic applications. Additionally, thermoelectric investigations showed that Cs2AgBiBr6 has a higher figure of merit, indicating better potential for thermoelectric applications.
This paper outlines the results of investigating the structural arrangement at different scales in additively manufactured Ti–6Al–4V and Ti–4Al–3V titanium alloys. The research indicates that both alloys display a notable anisotropy of structural and mechanical properties that is more pronounced in the alloy with reduced aluminum and vanadium levels. Increasing the alloying element content results in reduced grain size in the titanium alloy and alters its structural and phase characteristics. The development of a complicated structure comprising α2-Ti3Al, α”-Ti, and β-Ti phases in the α/β-lath structures results in enhanced strength characteristics of the Ti–6Al–4V alloy in comparison with the Ti–4Al–3V alloy, in which the primary structural elements following printing consist of the α-phase with a minor fraction of β-Ti phase interlayers. The alloys exhibit pronounced anisotropy in their mechanical response during quasistatic tensile tests as well as in fatigue and impact toughness evaluations. In tensile testing, the Ti–4Al–3V alloy samples tested in the diagonal direction display the greatest strength and the lowest ductility, while those tested in the growth direction show the lowest strength and the greatest ductility. The same tendency is also observed with the Ti–6Al–4V alloy, although it is less distinct. Although the average tensile strength of the Ti–6Al–4V alloy samples exceeds that of the Ti–4Al–3V alloy by over 200 MPa and the micro–hardness value by more than 1.0 GPa, the Ti–4Al–3V alloy demonstrates reasonable printability characteristics and can be utilized for producing components via the WEBAM method due to its lower cost.
We investigated the mechanical properties, microstructure, and fracture micromechanisms of austenitic stainless steel with a composition of Fe-17Cr-13Ni-1.7Mn-2.7Mo-0.5Si-0.01C (in mass.
Porous Ferromagnetic Shape Memory Alloy (FSMA) has excellent magneto mechanical properties. A micromechanical constitutive model based on the Eshelby equivalent inclusion theory and Mori–Tanaka (M-T) method is established, which can describe and predict the magneto–mechanical coupling behavior of porous FSMA. The numerical results are closer to the Couch’s experimental data, verifying the validity of the established model. The mechanical behavior of porous FSMA with different conditions of magneto–mechanical coupling is investigated. The results show that the maximum reorientation strain increases with the increase of the porosity, and the critical stresses at the beginning and end of the reorientation of porous FSMA increase with the increase of the magnetic field strength. In addition, the characteristics of equivalent elastic modulus, magnetic strain and magnetic stress of porous FSMA are also analyzed. The results of the study can provide a theoretical basis for the application of such materials in practical engineering.
