Search Results (258)

Atomic-scale strain is the basis of a material’s macroscopic deformation behavior. The current measure of atomic-scale strain in the form of the Green–Lagrange tensor loses its physical meaning beyond the yield point, as atomic neighborhoods undergo significant reconstructions. We have recently introduced a new atomic-scale strain measure, namely, atomic bond strain, through our study of bond behavior in multicomponent metallic glasses. Here, we apply this new strain measure to uniaxial tensile tests (simulated using molecular dynamics) of several representative single-crystal FCC (face-centered cubic) metals under varied strain rates. We show that this new strain measure displays remarkable near-linear correlation with stress, not only in the elastic regime, but also in the plastic regime where complex dislocation dynamics (nucleation, bursting, motion, annihilation, regeneration) and stress fluctuations take place. This suggests that the overall stress of the materials even in the plastic regime is predominantly determined by the degree of bond stretching among all atoms. This appears to contradict the common conceptions that the plastic flow stress of a crystalline material is governed by dislocation events involving only a small fraction of atoms around dislocations, and that the stress–strain relationship is highly non-linear for plastic deformation. The contradictions can be reconciled by considering the causal sequence: dislocation events alter bond stretching, and bond stretching directly determines the stress. This brings a novel insight into the nature of plastic deformation, owing to the newly introduced atomic bond strain. How well the near-linear correlation between the stress and the atomic bond strain holds in other materials (e.g., non-FCC single crystals, polycrystals, quasicrystals, elements, alloys, and compounds) is an intriguing and important topic for future investigation, following the example of this work. Full article

FeCoCrNiNb_xN (x = 0, 0.25, 0.5, 0.75, 1 molar) high-entropy nitride (HEN) films were fabricated on 304 stainless steel and Si wafers using magnetron sputtering to investigate the influence of Nb content on the microstructure, mechanical properties, and tribological performance. X-ray diffraction (XRD) analysis reveals a face-centered cubic (FCC) structure with a preferred orientation in the (200) plane, which transfers to the (111) plane as the Nb content increases. The lattice distortion induced by Nb incorporation enhanced crystallinity, with the Nb_0.5N film exhibiting the highest diffraction peak intensity and interplanar distance. Cross-sectional SEM images displayed columnar crystal structures, while the surface morphology evolved from “cauliflower-like” to smoother clusters with increasing Nb content, reducing average roughness from 7.54 nm (Nb₀) to 4.89 nm (Nb₁). The hardness and elastic modulus initially decrease, then peak at 25.56 GPa and 265.36 GPa, respectively, for the Nb₁ film, attributed to solid solution strengthening and high-entropy effects. Tribological tests demonstrated that Nb₁ achieved the lowest coefficient of friction (0.46), wear volume (1.23 × 10⁻³ mm³), and wear rate (5.11 × 10⁻⁸ mm³·N⁻¹·m⁻¹), owing to NbN phase formation, refined grains, and reduced surface roughness. The wear mechanisms are abrasive and oxidative wear. Full article

This study investigated the compatibility of lead with distinct crystal planes of Fe with a body-centered cubic (bcc) crystal structure and Ni with a face-centered cubic (fcc) crystal structure using molecular dynamics (MD) simulation. It was found that corrosion anisotropy depends mainly on the role of different crystal planes in regulating the spatial distribution of liquid lead. The essence of this regulation can be attributed to the interaction between the crystal plane and the liquid lead atoms. In consequence of the periodic arrangement of the crystal planes, the close-packed plane exhibits the highest atomic density and the widest interplanar distance. This configuration minimizes the interaction of the liquid lead atoms with the other crystal planes, thereby maximizing the regulatory effect on the distribution of the liquid lead atoms. The regulatory effect results in the formation of a regular layer-like distribution of the lead atoms, with a spacing between layers that is analogous to the crystal planes. This distribution mechanism effectively prevents the dissolution of atoms on the crystal surface into the liquid lead side by separating the atoms of the solid–liquid system from each other. Accordingly, for pure metals with a bcc crystal structure, corrosion resistance anisotropy indicates that the (111) plane is the most susceptible to corrosion, followed by the (001) plane, and the close-packed plane of (110) exhibits the most corrosion-resistant properties. As for fcc crystals, the corrosion resistance of the distinct planes is ordered as follows: (111) > (001) > (110). Full article

Alloy gradient-grained structures (represented by copper as a typical single-phase face-centered cubic (FCC) metal), known for their superior mechanical properties such as enhanced strength, ductility, and fatigue resistance, have become increasingly important in aerospace and automotive industries. These alloys are often fabricated using advanced processing techniques such as laser welding, electron beam melting, and controlled cooling, which induce spatial gradients in grain size and optimize material properties by overcoming the traditional strength–ductility trade-off. In this study, a deep learning-based inversion framework combining Convolutional Neural Networks (CNN) and Long Short-Term Memory (LSTM) networks is proposed to efficiently predict key constitutive parameters, such as the initial critical resolved shear stress and hardening modulus, in alloy gradient-grained structures. The model integrates spatial features extracted from strain-field sequences and grain morphology images with temporal features from loading sequences, providing a comprehensive solution for path-dependent mechanical behavior modeling. Trained on high-fidelity Crystal Plasticity Finite Element Method (CPFEM) simulation data, the proposed framework demonstrates high prediction accuracy for the constitutive parameters. The model achieves an error margin of less than 5%. This work highlights the potential of deep learning techniques for the efficient and physically consistent identification of constitutive parameters in alloy gradient-grained structures, offering valuable insights for alloy design and optimization. Full article

Intermetallic NiMn-based Heusler alloys (HAs) have garnered considerable attention due to their multifunctionality and applications in various fields, including sensors, actuation, refrigeration, and waste heat harvesters. Among the NiMn-based alloys, Ni-Mn-Sn alloys have gained considerable attention since their structural and magnetic transformations were discovered. Many studies have been conducted with various compositions and shapes to investigate the physical properties of Ni-Mn-Sn alloys, which offer several advantages, including non-toxicity, low cost, and abundant constituents. The Co-doping effect on the physical properties of Ni-Mn-Sn alloys has been widely reported. This doping can rectify the ternary Ni-Mn-Sn Heusler compound’s brittleness by crystallizing a disordered face-centered cubic (fcc) γ-phase. In this study, a polycrystalline Ni₄₂Mn₄₆CoSn₁₁ Heusler alloy was prepared by high-frequency fusion (HF), using a Lin Therm 600 device, from pure Ni, Mn, Sn, and Co elements with appropriate proportions. X-ray diffraction, scanning electron microscopy, and magnetic magnetometry devices were used to study the structural, microstructural, and magnetic properties. The XRD results revealed the coexistence of a disordered 7 M martensite phase (~88%) and a disordered cubic solid solution γ-phase (~12%). The alloy underwent a second-order ferromagnetic-to-paramagnetic phase transition at a Curie temperature of 350 K. Landau and Hamad’s theoretical models were used to plot the magnetic entropy change. The magnetocaloric properties (the maximum entropy change value, ΔS_M, the full width at half maximum of the entropy change curve, δT_FWHM, the relative cooling power, RCP, and the heat capacity, ΔC_P,H) were calculated using isothermal magnetization curves with the phenomenological model of Hamad. Full article

This study addresses the challenge of low-temperature synthesis of the high-performance L1₀ Fe-Pt intermetallic phase, which is critical for applications in ultra-high-density data storage and advanced magnetic devices. We demonstrate that the choice of iron precursor is a decisive factor in directing the phase composition and thermal evolution of Fe-Pt nanostructures, ultimately determining their suitability as functional composite materials. Fe-Pt systems were synthesized from aqueous solutions using platinum(IV) chloric acid (H₂PtCl₆) with either iron(III) ammonium sulfate (NH₄Fe(SO₄)₂) or iron(II) sulfate (FeSO₄). Comprehensive characterization using X-ray diffraction and high-resolution transmission electron microscopy revealed distinct composite formations. The iron(III) precursor yielded homogeneous, thermally stable nanocomposites: as-synthesized nanoparticles formed a Pt-based FCC solid solution (~5 nm), which upon annealing at 500 °C transformed into a biphasic nanocomposite of FCC solid solution and an L1₂ Fe₂₁Pt₇₉ intermetallic phase with minimal grain growth (~7 nm). In stark contrast, the system derived from iron(II) sulfate resulted in a heterogeneous composite of 4 nm Pt nanoparticles, an FCC solid solution, and discrete 1–3 nm Fe nanoparticles with L1₂-ordered FePt₃ domains. Annealing this heterogeneous mixture caused phase segregation, forming significantly coarsened Pt-rich crystals (~30 nm) that were approximately 4–6 times larger than the crystallites in the annealed homogeneous composite, with negligible Fe incorporation. Our findings establish that precursor chemistry dictates the initial nanocomposite architecture, which in turn controls the pathway and success of low-temperature intermetallic phase formation. This work provides a crucial design principle for fabricating tailored Fe-Pt composite nanomaterials, moving beyond simple alloys to engineered multiphase systems for practical application. Full article

FeCoNiCuAl high-entropy alloys exhibit remarkable mechanical properties; nevertheless, these materials struggle to withstand harsh environments because of their insufficient resistance to wear and corrosion. The addition of Si can significantly enhance the alloy’s high-temperature performance, hardness, and wear resistance, thereby making it more suitable for applications in high-temperature or corrosive environments. To overcome these drawbacks, this research investigates how varying Si content affects the microstructure and properties of FeCoNiCuAl coatings. Composite coatings of FeCoNiCuAlSi_x (x = 0, 0.5, 1.0, 1.5, 2.0) were fabricated on 65 Mn substrates using laser cladding. Various testing methods, including metallographic microscopy, Vickers hardness testing, friction and wear testing, and electrochemical analysis, were employed to examine the phase structure, microstructure, and hardness of the coating. It is observed that the FeCoNiCuAl coating begins with a uniform FCC phase structure. However, as the Si content increases, a phase transformation to the BCC structure occurs. The microstructure is primarily composed of isometric crystals and dendrites that become finer and more compact with higher Si content. For the FeCoNiCuAlSi_2.0 coating, the microhardness reaches 581.05 HV_0.2. Additionally, wear resistance shows a positive correlation with Si content. Electrochemical testing in NS4 solution shows that the corrosion potential of the coating increases from −0.471 V for FeCoNiCuAl to −0.344 V for FeCoNiCuAlSi_2.0, while the corrosion current density decreases from 1.566 × 10⁻⁶ A/cm² to 4.073 × 10⁻⁶ A/cm². These results indicate that Si addition plays a crucial role in enhancing the mechanical properties and corrosion resistance of FeCoNiCuAl coatings, making them more suitable for high-performance applications in extreme environments. Full article

Molecular dynamics (MD) can dynamically reveal the structural evolution and mechanical response of Zirconium (Zr) at the atomic scale under complex service conditions such as high temperature, stress, and irradiation. However, traditional empirical potentials are limited by their fixed function forms and parameters, making it difficult to accurately describe the multi-body interactions of Zr under conditions such as multi-phase structures and strong nonlinear deformation, thereby limiting the accuracy and generalization ability of simulation results. This paper combines high-throughput first-principles calculations (DFT) with the machine learning method to develop the Deep Potential (DP) for Zr. The developed DP of Zr was verified by performing molecular dynamic simulations on lattice constants, surface energies, grain boundary energies, melting point, elastic constants, and tensile responses. The results show that the DP model achieves high consistency with DFT in predicting multiple key physical properties, such as lattice constants and melting point. Also, it can accurately capture atomic migration, local structural evolution, and crystal structural transformations of Zr under thermal excitation. In addition, the DP model can accurately capture plastic deformation and stress softening behavior in Zr under large strains, reproducing the characteristics of yielding and structural rearrangement during tensile loading, as well as the stress-induced phase transition of Zr from HCP to FCC, demonstrating its strong physical fidelity and numerical stability. Full article

This study examines the mechanical, thermal, and electrical properties of copper tool electrodes processed via Equal Channel Angular Pressing (ECAP), with a specific focus on their performance in Electrical Discharge Machining (EDM) applications. A novel Crystal Plasticity Finite Element Method (CPFEM) framework is employed to model anisotropic slip behavior and microscale deformation mechanisms. The primary objective is to elucidate how initial crystallographic orientation influences hardness, thermal conductivity, and electrical conductivity. Simulations are performed on single-crystal copper for three representative Face Centered Cubic (FCC) orientations. Using an explicit CPFEM model, the study examines texture evolution and deformation heterogeneity during the ECAP process of single-crystal copper. The results indicate that the <100> single-crystal orientation exhibits the highest Taylor factor and the most homogeneous distribution of plastic equivalent strain (PEEQ), suggesting enhanced resistance to plastic flow. In contrast, the <111> single-crystal orientation displays localized deformation and reduced hardening. A decreasing Taylor factor correlates with more uniform slip, which improves both electrical and thermal conductivity, as well as machinability, by minimizing dislocation-related resistance. These findings make a novel contribution to the field by highlighting the critical role of crystallographic orientation in governing slip activity and deformation pathways, which directly impact thermal wear resistance and the fabrication efficiency of ECAP-processed copper electrodes in EDM. Full article

In order to enhance the performance of 20# steel, this study successfully fabricated AlCoCrFeNi high-entropy alloy coatings with different WC contents (x = 0, 10, 20, 30 wt%) on its surface using plasma cladding technology. The effects of WC content on the microstructure, mechanical properties, and corrosion resistance of the coatings were systematically investigated. The results indicate that without WC addition, the coating consists of a dual-phase structure comprising BCC and FCC phases. With the incorporation of WC, the FCC phase disappears, and the coating evolves into a composite structure based on the BCC matrix, embedded with multiple carbide phases such as W₂C, M₇C₃, M_xC_γ, and Co₆W₆C. These carbides are predominantly distributed along grain boundaries. As the WC content increases, significant grain refinement occurs and the volume fraction of carbides rises. The coating exhibits a mixed microstructure of equiaxed and columnar crystals, with excellent metallurgical bonding to the substrate. The microhardness of the coating increases markedly with higher WC content; however, the rate of enhancement slows when WC exceeds 20 wt%. The hardness of 1066.36 HV is achieved at 30 wt% WC. Wear test results show that both the friction coefficient and wear rate first decrease and then increase with increasing WC content. The optimal wear resistance is observed at 20 wt% WC, with a friction coefficient of 0.549 and a wear mass loss of only 0.25 mg, representing an approximately 40% reduction compared to the WC-free coating. Electrochemical tests demonstrate that the coating with 20 wt% WC facilitates the formation of a dense and stable passive film in NaCl solution, effectively inhibiting Cl⁻ ion penetration. This coating exhibits the best corrosion resistance, characterized by the lowest corrosion current density of 1.349 × 10⁻⁶ A·cm⁻² and the highest passive film resistance of 2764 Ω·cm². Full article

Based on first-principles calculations, we systematically investigate the crystal structure, electronic structure, and superconductivity of metallic lead under pressure. The results show that with the increase of pressure, the crystal structure of lead evolves from face-centered cubic (fcc) to hexagonal close-packed (hcp) and then to body-centered cubic (bcc). In different crystal structure phases, the variation laws of electronic structure and superconducting properties with pressure are studied. It is found that the superconducting transition temperature decreases with the increase of pressure in fcc, hcp, and bcc phases. The physical mechanism for this change is explained. The calculation results indicate that elemental metallic lead remains metallic with the increase of pressure, but the electron density of states at the Fermi level decreases, leading to the decrease of the electron-phonon coupling constant ($\lambda$) and superconducting transition temperature ($T_c$) from 7.1 K to 0.04 K. In addition, with the increase of pressure, there is no phenomenon of s electrons transforming into d electrons, which is different from the superconducting behavior of zirconium metal under pressure. These studies explain the superconductivity of elemental metallic lead under high pressure and provide theoretical support for the experiments and applications of lead-based superconductors. Full article

The effects of Cu content on the microstructure, texture, precipitates, and magnetic and mechanical properties of 0.20 mm-thick non-oriented silicon steel (3.0% Si-0.8% Al-0.5% Mn) were systematically investigated using optical microscopy, X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. The strengthening mechanisms of Cu-bearing high-strength non-oriented silicon steel were further elucidated. Increasing Cu content inhibited grain growth and suppressed the development of the α*-fiber texture in annealed sheets, while promoting the formation of γ-fiber texture. As a result, the P_1.0/400 and B₅₀ values deteriorated. The P_1.0/400 and B₅₀ values of 1.47% Cu non-oriented silicon steel were 13.930 W/kg and 1.614 T, respectively. However, due to the solid solution strengthening effect of 0.5% Cu and partial precipitation strengthening, the R_p0.2 increased by 43 MPa. After aging treatment at 550 °C for 20 min, the P_1.0/400 values of the aged sheets slightly increased, while the B₅₀ values remained almost unchanged. In the aged sheets containing 1.0–1.5% Cu, clustered Cu-rich precipitates with average sizes of 2.71 nm and 13.28 nm were observed. The crystal structure of these precipitates transitioned from the metastable B2-Cu to the stable FCC-Cu. These precipitates enhanced the R_p0.2 of the non-oriented electrical steel to 241 MPa and 269 MPa through cutting and bypass mechanisms, respectively. A high-strength non-oriented silicon steel with balanced magnetic and mechanical properties was developed for driving motors of new energy vehicles by utilizing nanoscale Cu-rich precipitates formed through aging treatment. The optimized steel exhibits a yield strength of 708 MPa, a magnetic induction B₅₀ of 1.639 T, and high-frequency iron loss P_1.0/400 of 14.77 W/kg. Full article

The effect of dislocation pile-ups responsible for the generation or annihilation of dislocations during friction of Ag and Ni was considered. The steady-state friction was accompanied by the formation of twin bundles, intersecting twins, dislocations, adiabatic elongated shear bands, and intense dynamic recrystallization. The mechanisms of microstructural stability and friction instability were analyzed. The theoretical models of dislocation generation and annihilation in nanocrystalline FCC metals in the context of plastic deformation and failure development under friction were proposed. The transition to unstable friction was estimated. The damage of Ag was exhibited in the formation of pores, reducing the contact area and significantly increasing the shear stress. The brittle fracture of Ni represents a catastrophic failure associated with the formation of super-hard nickel oxide. Deformation resistance of the dislocation structures in the mesoscale and macroscale was compared. The coefficient of similitude (K) has been introduced in this work to compare plastic deformation at different scales. The model of the strength–ductility trade-off and microstructural instability is considered. The interaction between the migration of dislocation pile-ups and the driving forces applied to the grain boundaries was estimated. Nanostructure stabilization through the addition of a polycrystalline element (solute) to the crystal interiors in order to reduce the free energy of grain boundary interfaces was investigated. The thermodynamic driving force and kinetic energy barrier involved in strengthening, brittleness, or annealing under plastic deformation and phase formation in alloys and composite materials were examined. Full article

The present study focused on 10 wt.% TiB₂@Ti/AlCoCrFeNi_2.1 eutectic high-entropy alloy matrix composites (EHEAMCs), which were treated with furnace cooling (FC), air cooling (AC), and water cooling (WC) after being held at 1000 °C for 12 h, aiming to investigate the effect of cooling methods on their microstructure and mechanical properties. The results showed that the composites in all states consisted of FCC phase, BCC phase, TiB₂ phase, and Ti phase. The cooling methods did not change the phase types but affected the diffraction peak characteristics. With the increase in cooling rate, the diffraction peaks of FCC and BCC phases gradually separated from overlapping, and the diffraction peak of the FCC (111) crystal plane shifted to a lower angle (due to the increase in lattice constant caused by Ti element diffusion), while the diffraction peak intensity showed a downward trend. In terms of microstructure, all composites under the three cooling conditions were composed of eutectic matrix, solid solution zone, and grain boundary zone. The cooling rate had little effect on the morphology but significantly affected the element distribution. During slow cooling (FC, AC), Ti and B diffused sufficiently from the grain boundary to the matrix, resulting in higher concentrations of Ti and B in the matrix (Ti in FCC phase: 7.4 at.%, B in BCC phase: 8.1 at.% in FC state). During rapid cooling (WC), diffusion was inhibited, leading to lower concentrations in the matrix (Ti in FCC phase: 4.6 at.%, B in BCC phase: 4.3 at.%), but the element distribution was more uniform. Mechanical properties decreased with the increase in cooling rate: the FC state showed the optimal average hardness (627.0 ± 26.1 HV), yield strength (1574 MPa), fracture strength (2824 MPa), and fracture strain (24.2%); the WC state had the lowest performance (hardness: 543.2 ± 35.4 HV and yield strength: 1401 MPa) but was still better than the as-sintered state. Solid solution strengthening was the main mechanism, and slow cooling promoted element diffusion to enhance lattice distortion, achieving the synergistic improvement of strength and plasticity. Full article

We investigate TiAlZrTaNb nitride coatings deposited on Haynes 282 nickel superalloy substrates via high-power impulse magnetron sputtering (HiPIMS) under varying substrate bias voltages (0 V to −75 V). The influence of substrate bias on the microstructure, morphology, hardness, and wear resistance was systematically analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and ball-on-disk tribometry. The coatings exhibited a near equiatomic chemical composition with a face-centered cubic (FCC) crystal structure preferentially oriented along the (200) and (111) planes. Increasing the bias voltage reduced the grain size (3.65 nm to 2.84 nm) and lattice parameter (0.442 nm to 0.440 nm); meanwhile, the hardness (>45 GPa) and wear resistance were improved. The interplay between the deposition parameters and coating-substrate interactions are discussed in order to optimize HiPIMS-derived coatings for industrial applications. Full article