Atoms In Solid Solution Research Articles

Cu-Atom Locations in Rocksalt SnTe Thermoelectric Alloy.

The development of functional thermoelectric materials requires direct evidence of dopants' locations to rationally design the electronic and phononic structure of the host matrix. In this study, Cs-corrected scanning transmission electron microscopy and energy dispersive X-ray spectroscopy is employed at the atomic scale to identify Cu atoms' locations in a Cu-doped SnTe thermoelectric alloy. It is revealed that Cu atoms in the rocksalt SnTe form solid solutions at both Sn and Te sites, contrary to their electronegativity order and the intentional Cu doping at Sn sites. Cu atoms are also located at the tetrahedral and crowdion sites of the face-centred cubic structure, with varying degrees of correlations. Such high flexibility of Cu atoms in the rocksalt SnTe offers diverse phonon-scattering mechanisms conducive to the ultra-low lattice thermal conductivity of singly Cu-doped SnTe. This study offers atomic-scale insights for achieving more precise dopant engineering, leading to the accelerated development of functional thermoelectric materials.

Ferritic–Martensitic Steels in Power Industry: Microstructure, Degradation Mechanism, and Strengthening Methods

Ferritic–martensitic (F–M) steels are widely used for high‐temperature pressure vessels and reactor cladding structures in power plants. The high operating temperatures and pressures, as well as the radiation environment, significantly challenge the mechanical stability of these steels. Here, the degradation mechanisms in F–M steels during creep and thermal aging under these harsh environments are reviewed. The exceptional mechanical properties of F–M steels are mainly attributed to their well‐constructed microstructures and chemical compositions. Microstructural barriers such as dislocations, solid solution atoms, and precipitates play key roles in resisting degradation. During the long‐term service, the microstructures undergo gradual evolution, resulting in a deterioration of mechanical properties at the macrolevel. In addition to the degradation mechanisms, some recent advancements in strengthening methods, including microalloying strengthening, thermomechanical treatment (TMT), and oxide dispersion strengthening, are summarized, aimed at the development of next‐generation F–M steels. The strengthening of the F–M steels is mainly achieved by enhancing the thermal stability of their microstructures. Insight into both the deterioration mechanisms and strengthening methods of F–M steels may pave the way for new approaches in developing high‐performance steels for applications in next‐generation power plants operating at ultrahigh operating temperatures and pressures.

Microstructure and mechanical properties of cast, eutectic Al-Ce-Ni-Mn-Sc-Zr alloys with multiple strengthening mechanisms

The effects of Ni additions on microstructure and microhardness of near-eutectic Al-9Ce-xNi-0.75Mn-0.18Sc-0.12Zr (x = 2.5, 3.2, and 3.9 wt.%) alloys are investigated for various cooling rates. The as-cast microstructure consists of fine, micron-scale Al11Ce3 and Ni-rich phases formed during eutectic solidification. Two Ni-rich phases are observed: (i) Al27Ce3Ni6 at higher Ni contents and slower solidification rates, and (ii) Al9(Ni,Mn,Fe)2 at lower Ni contents and faster solidification rates. While these Ni-containing alloys have higher microhardness than a Ni-free control alloy, varying the Ni concentration in the 2.5–3.9 wt.% range does not significantly affect the microhardness, indicative of competing strengthening and weakening effects from adding Ni. The alloy with intermediate Ni content (3.2 wt.%) is selected for further microstructural and mechanical characterization. It contains four coarsening-resistant strengthening constituents: (i) micron-scale Al11Ce3 and (ii) Al27Ce3Ni6 or Al9(Ni,Mn,Fe)2 platelets, all formed during eutectic solidification, (iii) L12-Al3(Sc,Zr) nanoprecipitates formed on aging, and (iv) Mn atoms in solid solution in the α-Al matrix. The combined strengthening mechanisms impart high strength at ambient and elevated temperatures, as measured by microhardness (as a function of aging time), by compression and tensile experiments, and by compressive creep measurements. Alloys previously reported in the literature - with various combinations of one, two or three of these four strengthening phases - show lower hardness and creep resistance, indicating that cumulative strengthening can be achieved when combining mechanisms; the present alloy containing all four phases shows a remarkably high creep threshold stress of 62 MPa at 300 °C.

Superior strength and electrical conductivity synergy of cold‐drawn Al‐Mg‐Si‐Ce‐Cu wires produced by continuous casting and rolling

Al‐Mg‐Si aluminum wires for overhead power transmission have extensive applications in industry and daily life. In this study, superior strength and electrical conductivity combination in the aged cold‐drawn Al‐Mg‐Si‐Ce‐Cu wires fabricated by continuous casting and rolling are achieved. The cold‐drawn wires exhibit high strength and electrical conductivity combinations of 383±2 MPa, 51.16±0.23% IACS; 373±3 MPa, 51.98±0.25% and 357±3 MPa, 53.16±0.11% IACS, respectively, when aged at 160 °C, 170 °C or 180 °C for 24 h. Subgrain boundaries are introduced into alloys by continuous casting and rolling and cold drawing, causing significant lattice distortion within the grains and providing sites for the nucleation of precipitates. Moreover, HADDF‐STEM (high‐angle annular dark‐field scanning transmission electron microscopy) and DFT (density functional theory) results show that Ce atoms could enter the lattice of β” and replace the Si3 sites, which is energetically preferred. The underlying mechanisms for achieving superior strength‐electrical conductivity combination are to introduce subgrain boundaries via continuous casting and rolling and cold drawing for promoting the transformation of solid solution atoms to finely dispersed precipitates, which significantly reduces the scattering of electrons and hence improves the electrical conductivity. This work provides a new strategy for designing high‐strength and high‐conductivity aluminum alloy wire conductors.This article is protected by copyright. All rights reserved.

High-temperature corrosion behavior of the FeCrAl laser cladding coatings in waste-to-energy superheaters: Influence of Al content

Enhancing the high-temperature corrosion resistance of superheaters in waste-to-energy plants (WTE) is key to improving the efficiency of WTE power generation. The present study employed laser cladding technology to fabricate Fe-13Cr-xAl coatings, and characterized the microstructure, phase structure, and Vickers hardness of the coatings using OM, SEM, XRD, and a Vickers hardness tester. The study investigated the influence of high-temperature corrosion resistance of the coatings under simulated WTE flue gas conditions. This study found that: Al and Cr both exist in the form of solid solution atoms in the laser cladding coatings. The Vickers hardness of the coatings gradually increased with increasing Al content. When the Al content exceeds 10 %, cracks begin to appear in the coatings, and the number and size of cracks increase with increasing Al content. The Fe-13Cr-7Al coatings exhibit the best high-temperature corrosion resistance under simulated WTE flue gas conditions, and it can achieve ∼73 % of the high-temperature corrosion resistance of the Inconel 625 alloy laser cladding coatings. During high-temperature corrosion, phase separation occurs near the grain boundaries, resulting in chromium depletion zones, which promote intergranular corrosion of the coatings. During the process of high temperature corrosion, the reactions between Al, Cl, and S exhibit the lowest Gibbs free energy. The continuous consumption of Al effectively protects the Fe and Cr in the substrate. Additionally, the formation of aluminum oxide in the coating hinders the inward diffusion of Cl2, thereby beneficially impeding the progress of corrosion. Excessive Al contents in the coatings introduced cracks that served as channels for molten salt to penetrate the matrix, thereby reducing the high-temperature corrosion resistance of the coatings.

Superior specific capacity and energy density simultaneously achieved by Sr/In co-deposition behavior of Mg-Sr-In ternary alloys as anodes for Mg-Air cells

In this work, the combined addition of strontium/indium (Sr/In) to the magnesium anode for Mg-Air Cells is investigated to improve discharge performance by modifying the anode/electrolyte interface. Indium exists as solid solution atoms in the α-Mg matrix without its second-phase generation, and at the same time facilitates grain refinement, dendritic segregation and Mg17Sr2-phases precipitation. During discharge operation, Sr modifies the film composition via its compounds and promoted the redeposition of In at the substrate/film interface; their co-deposition behavior on the anodic reaction surface enhances anode reaction kinetics, suppresses the negative difference effect (NDE) and mitigates the “chunk effect” (CE), which is contributed to uniform dissolution and low self-corrosion hydrogen evolution rate (HER). Therefore, Mg-Sr-xIn alloy anodes show excellent discharge performance, e.g., 0.5Sr-1.0In shows an average discharge voltage of 1.4234 V and a specific energy density of 1990.71 Wh kg−1 at 10 mA cm−2. Furthermore, the decisive factor (CE and self-discharge HE) for anodic efficiency are quantitively analyzed, the self-discharge is the main factor of cell efficiency loss. Surprisingly, all Mg-Sr-xIn anodes show anodic efficiency greater than 60% at high current density (≥10 mA cm−2), making them excellent candidate anodes for Mg-Air cells at high-power output.

The new sight to Fe–C system

ABSTRACT The crystalline Fe–C alloy had been the focal point of research in the traditional metallurgical steel industry. However, its corresponding amorphous alloy system had received little attention, with a lack of consensus on the microstructural evolution. Three types of Fe–C unbalanced composite films with different carbon content were fabricated using the magnetron sputtering method. The results indicated that as the carbon content increased, carbon existed in the form of supersaturated solid solution atoms in crystalline Fe, an amorphous Fe–C structure and Fe3C, respectively. The resistivity of the films in these three carbon types gradually increased from 1.37 × 10−4 ohm/cm to 4.53 × 10−2 ohm/cm and then to 5.43 × 10−2 ohm/cm. Simultaneously, the transmittance gradually increased from 0% to 28% and then to 51%. Upon annealing at 400°C, with the crystallisation of Fe in the low-carbon film, unbalanced carbon atoms were pushed out of the lattice and precipitated as Fe3C. After annealing at 650°C, the Fe3C in the high-carbon film decomposed into Fe and C. The as-prepared medium-carbon film displayed commendable corrosion resistance. These findings provided valuable insights for the design and performance development of new materials.

Strength-ductility materials by engineering a coherent interface at incoherent precipitates.

In the quest for excellent light-structural materials that can withstand mechanical extremes for advanced applications, design and control of microstructures beyond current material design strategies have become paramount. Herein, we design a coherent shell at incoherent precipitates in the 2195 aluminum alloy with multi-step metastable phase transitions. A high local strain rate via a neoteric deformation-driven metallurgy method facilitated the diffusion of Li. The original T1 (Al2CuLi) phases were transformed into coherent-shell (Li-rich) irregular-coated incoherent-core (Al2Cu) precipitates. The ultimate tensile strength and elongation reached 620 ± 18 MPa and 22.3 ± 2.2%, exhibiting excellent strength-ductility synergy. Grain boundaries, dislocation, solid solution atoms, and precipitates all contributed to the yield strength of the materials, among which precipitates occupied a dominant position, contributing approximately 56.07%. A new "incoherent-coherent interact" strain-hardening mechanism was also clarified, which was believed to be promoted in other heat-treatable alloy systems, especially with multi-step metastable phase transitions.

The influence of Zr concentration on the microstructure and properties of Cu-0.6Cr-xZr alloy: High-throughput preparation and characterization study

In this work, the high throughput sample of Cu-0.6Cr-xZr (x = 0–0.18 wt%) alloy was prepared using spark plasma sintering. The influence of Zr concentration on the microstructure and properties of Cu alloys were investigated through advanced characterization technique. The findings reveal that the Zr element concentration in the Cu alloy exhibits a gradient distribution after aging treatment at 500 °C. Some Zr elements precipitate as Cu2Zr phase at a certain Zr concentration of 0.14 wt%. The alloy's hardness increases, while its conductivity decreases with the Zr concentration increasing, attributed to the impediment of dislocation and electron movement caused by solid solution atoms, grain boundaries, and precipitated phases.

The Influence of Substitutional Defects of Transition Metal Elements on the Stability and Thermal Properties of Al at Finite Temperatures: A First-Principles Study

Based on first-principles calculations, the effects of substitutional defects of the 3d–5d transition metal elements TMAl on the stability and thermal conductivity of the aluminum matrix were investigated. The results show that with an increase in the atomic number of TM, the defect-forming energy Ef of TMAl exhibits a periodic change feature, which depends on the valence electron configuration of the TM elements. The thermodynamic property parameters calculated with the Debye theory show that the addition of TM atoms does not change the stability of an Al system and can effectively reduce the thermal expansion coefficient of the material. But the equilibrium lattice constant a0 of Al-TMAl supercells changes very little. As the temperature increases, the relaxation time τ decreases, and both the electronic thermal conductivity κe and the total thermal conductivity κ decrease at the temperature range of 100–200 K, followed by a small increase or decrease. Because the lattice thermal conductivity κl is very small in the whole temperature range, the changes in electronic thermal conductivity and total thermal conductivity are basically the same. Moreover, when 1 at.% TM was added at both 300 K and 600 K, it was found that the influence of TM solute atoms on the thermal conductivity κ of Al was much greater than that of the second-phase particles. For solid solution atoms, Pd and Pt atoms have the greatest influence on the thermal conductivity of pure Al. This work is helpful for designing high-performance, heat-resistant Al-based alloys.

Drop That Activation Energy: Tetragonal to Cubic Transformations in Na3PS4−xSex for Solid State Sodium Ion Battery Materials

AbstractSodium‐containing chalcogenide materials are emerging as a class of solid electrolytes for application in inexpensive all‐solid‐state sodium‐ion batteries due to their high ionic conductivity, abundance, and degree of synthetic and structural variability. Members of the solid solution Na3PS4−xSex, which are promising solid electrolytes for sodium‐ion batteries, are prepared by reaction at high temperature. With increasing substitution of S by Se, the structure transforms from tetragonal (space group P21c for x = 0, 1) to cubic (space group I3m for x = 2, 3, 4). Within the solid solution, the S and Se atoms are completely disordered in the environments around the P atoms, in accordance with a binomial distribution, as inferred by the 31P nuclear magnetic resonance (NMR) spectra. In 23Na NMR experiments conducted at different magnetic fields and temperatures, quadrupolar lineshapes are observed that are influenced by sodium ion dynamics; the activation energies decrease from 0.21 to 0.15 eV on progressing from the S‐ to the Se‐rich members. A dynamic model is proposed to account for the changes in the 23Na quadrupolar lineshapes by switching the orientations of the electric field gradient and chemical shift anisotropy tensors when Na+ ions hop to the four nearest Na sites.

Contribution of the Fe-rich phase particles to the high temperature mechanical behaviour of an Al-Cu-Fe alloy

The high temperature strengthening mechanisms in Al-Cu-Fe aluminium alloy was analysed basis on a comprehensive microstructural study of the as-cast alloy and mechanical testing results. An approach which extracts the specific contribution of solid solution atoms, precipitates, and Fe-rich particles to the creep strengthening was utilized. Additionally, the Shear Lag model, was employed to account for the contribution to strengthening of the Fe-rich intermetallic particles through a load transfer mechanism. For this study, an as-cast Al-Cu alloy, which does not contain Fe impurities, has been also used for comparative purposes. The findings suggest that the large and 3D interconnected Fe-rich phase particles (Al6(MnFe) and α-Fe) generate the main strengthening effect at high temperature through a load transfer mechanism, whereas the contribution of the nanometric Al2CuMg precipitates were very limited.

High-throughput study of the effect of indium on the microstructure and properties of copper alloy

In this work, the high throughput sample of Cu-xIn (x = 0–5 wt.%) alloy was prepared by the spark plasma sintering. The effects of In content on the microstructure and properties of Cu alloys were investigated using advanced characterization. The results show that the concentration of In element linearly distributes in Cu alloy after annealing treatment at 450 °C. Most In elements exist in the Cu matrix as the solid solution atoms. Some In elements are precipitated at the grain boundaries as Cu9In4 particles when the In content is higher. The hardness of the alloy increases, while the conductivity decreases with the increase of In content, which is due to the hindrance of the movement of dislocations and electrons by solid solution atoms, grain boundaries, and Cu9In4 particles. The investigation of high throughput samples can provide data support for high strength and high conductivity Cu alloys.

Temperature-dependent tensile deformation and plasticity loss mechanism of a novel Ni-Cr-W-based superalloy prepared by laser powder bed fusion

The Ni-Cr-W-based Haynes 230 alloy fabricated by laser-beam powder bed fusion (PBF-LB) has garnered considerable attention for its ample shaping freedom and remarkable strength-plasticity synergy at room temperature. However, the limited strengthening effects provided by solid-solution atoms and carbides might restrict the practical applications of the alloy at high temperatures. In this paper, the high-temperature microstructural evolution and tensile properties of a novel γ′-strengthened based on Haynes 230 prepared by PBF-LB were systematically explored. The γ′ strengthening mechanism at 25–1000 °C and plasticity loss mechanism at 800–900 °C were first discussed. The results show that the precipitation of nanoscale γ′ phases after heat treatment (HT) can significantly improve the alloy strength at 25 °C, but dramatically sacrifice the alloy plasticity. With the testing temperature increasing, the ultimate tensile strength (UTS) and yield strength (YS) of the HT sample continue to decrease, while its elongation (EL) decreases first and then increases. A sharp decrease in EL appears at 900 °C, which is mainly attributed to the formation of acicular δ phases. The YS of the as-built (AB) sample from 25 °C to 800 °C increases, even higher than that of the HT sample, which is ascribed to the appearance of nanosized γ′ particles. The precipitation of γ′ particles and δ phases in the AB sample is the main reason for the more significant plasticity loss at 800–900 °C. Due to the increase in γ′ size and decrease in γ′ volume fraction, the dominant deformation mechanism in the HT sample changes from SF shearing at 25–800 °C to Orowan looping at 900–1000 °C.

Density functional study of atomic arrangements in CrMnFeCoNi high-entropy alloy and their impact on vacancy formation energy and segregation

Using the density functional theory-coupled Monte Carlo approach, we explored the chemical short-range order (SRO) and element segregation in equimolar CrMnFeCoNi alloy. We found that state-of-the-art approximation of random element distribution is only applicable at > 1100 K close to the melting temperature, while the Cr-Cr repulsion driving the system stabilization and accompanying the formation of cubic Cr sublattice, and mild Ni-Ni attraction are the most prominent pair interactions at lower temperatures. Chemical potential and vacancy formation energy calculations indicate that Cr is most sensitive to the local chemical environment, making Cr atoms most stabilized when the preferred SRO is introduced. While the vacancy formation is predicted equally probable among five constituting elements in the random solid solution, Cr and Ni atoms show the lowest vacancy formation energies in the structure with SRO. Furthermore, distinct element segregation was predicted in the vicinity of planar defects, including symmetric tilt grain boundary and stacking fault, which we correlated to the site- and chemistry-dependent atomic volume and bond lengths. It suggests that the local mechanical strain and bond energy induce the SRO development and element segregation: Namely, the system takes advantage of segregation of Ni atoms having large atomic volume or Cr-Cr pairs having elongated bond lengths to fill in the excess volume at defects that relaxes the mechanical strain field and optimizes bond energy distribution. The correlation between the SRO and properties of CrMnFeCoNi alloy needs further investigations, which is expected to greatly help understand and control the properties of high-entropy alloys.

Numerical study of the effective thermal conductivity of 2-phase magnesium alloys containing solid solution atoms using lattice Monte-Carlo

The assessment of thermal conductivity in alloy plays a crucial role in ensuring their stability and performance in thermal applications. This paper specifically focuses on simulating the thermal conductivity of complex microstructures, which involve solid solution atoms and second phases. The lattice Monte Carlo (LMC) method is employed to examine the effective thermal conductivity of the Mg-(Ce, La) model alloy. The results obtained from numerical simulation are compared to experimental data, demonstrating a good agreement between them. Additionally, the study establishes a correlation between the content of solid solution atoms and thermal resistance through rj,α = A/(1-2x). Furthermore, the impact of various factors, such as volume fraction (fβ), size (Z), and morphology (F‾) of the second phase on the effective thermal conductivity, is thoroughly investigated and summarized. Overall, this research contributes to a better understanding the thermal conductivity behavior in complex alloy microstructures.

Effect of Cu addition on the microstructure, mechanical properties and thermal properties of Mg-Al-Ca-Mn alloy

In this paper, Mg-Al-Ca-Mn-Cu magnesium alloys by Cu alloying were studied with the aim of developing Mg alloys with higher heat conduction. As a result, the mechanical properties and thermal conductivity of the alloys was evaluated simultaneously, owing to the addition of Cu, which meets the requirements of the project to develop high-strength and high-conductivity magnesium alloy. Compared with the commercial AZ31 magnesium alloy, the strength and plasticity are improved by means of fine grain strengthening. Meanwhile, the amount of solid solution atoms in the alloy decreases, and the content of the second phase particles increases, which reduces the degree of lattice distortion. On the other hand, the Cu element provides a large amount of free electron for heat transfer, which makes the alloys have a high thermal conductivity.

Effect of Mg content on the microstructure and properties of high strength, high conductivity Cu–Fe–Cr–Si–Mg alloy

A new strategy for the preparation of Cu–Fe alloy with excellent comprehensive performance is proposed. This strategy combines the construction of dual-scale polymetallic second phases with the addition of trace solid-solution atoms. A series of Cu–2Fe-0.3Cr-0.2Si-xMg (x = 0.1, 0.3, 0.5) alloys are designed and prepared through multi-stage thermo-mechanical treatment. Among the reported Cu–Fe alloys with low Fe content (Fe content less than 3 wt%), the designed Cu–2Fe-0.3Cr-0.2Si-0.3 Mg alloy has the highest product of the tensile strength times the electrical conductivity (PSC). The tensile strength and PSC of the Cu–2Fe-0.3Cr-0.2Si-0.3 Mg alloy are 698 MPa and 43.9 GPa∙%IACS, respectively. The dual-scale polymetallic second phase has been successfully constructed. The submicron-scale Fe8CrSi phase triggers the generation of substructures, such as geometrically necessary dislocation boundaries in lamellar structures and random dislocation boundaries in cell shapes. The high-density low angle grain boundaries (LAGBs) of substructure evolution enhances the substructure strengthening of the alloy. The main strengthening phase in precipitation strengthening is the nanoscale Fe11CrSi4 phase. An appropriate amount of Mg reduces the ultimate solid solubility of Fe atoms in Cu alloys, promotes the formation of a dual-scale second phase and refines the grain size of the alloy. Therefore, the comprehensive performance of the design alloy is significantly improved.

The nanoscale mechanisms of strengthening and ductility enhancement in an Al–Mg–Si–Mn alloy on processing by high-pressure torsion

In this work we show that high-pressure torsion (HPT) processing of an Al-1.0at%Mg-0.8at%Si-0.2at%Mn in T6 state causes an 81% increase in ultimate tensile strength (UTS) to reach 559 MPa, whilst, remarkably, retaining a very good ductility of 14%. After an initial decrease in ductility for up to 1 HPT turn, further deformation up to 5 turns remarkably causes increases in ductility as well as increases in hardness and UTS. Analysis by X-ray diffraction line broadening and transmission electron microscopy show that during HPT processing a high density of dislocations are produced, and the grain size decreases from 3 μm for T6 sample to around 286 nm for 5r-HPT sample. Atom probe tomography reveals solute atoms strongly segregate on ultrafine-grained boundaries for a 5r-HPT sample. A model for the strengthening mechanisms is established to evaluate contribution of dislocations, grain boundaries, solid solution atoms, precipitates and solute (co-)clusters. We show that in the HPT processed 6xxx-series Al–Mg–Si alloy the strengthening caused by solute segregation at dislocations and on grain boundaries is the dominant strengthening mechanism. This work illustrates a rare case of a beneficial concomitant increase of strength and ductility during HPT. The result is an AA6xxx material with strongly increased strength and very good ductility as compared to the widely employed commercially available AA6xxx-T6 alloys.

Molecular Dynamics Simulation of Solution Strengthening of Si and Cu Atoms in Aluminum Alloy

For heat‐treatable aluminum alloys, solid solute elements play key role in material strengthening. Al–Mg–Si alloy is a typical heat‐treatable alloy; Cu and Si atoms are its main solid solution atoms. To reveal the strengthening mechanism, the interaction between the edge dislocations and the Cu and Si solute atoms of different concentration in aluminum matrix is investigated by molecular dynamics (MD) simulation. Results indicate that Cu atoms provide a more effective strengthening due to the stronger pinning effect. The increment of critical resolved shear stress (ΔCRSS) is a function of concentration of solid solute atoms. When more than two types of solid solution atoms coexist in matrix, the final increment of the ΔCRSS is determined by the interactive effects of the atoms instead of the direct sum of all items. The pinning of Cu solid solute atoms can lead to two Shockley partial dislocations merging to an edge dislocation.