Solid Atoms Research Articles

Investigation of Two-Dimensional Geometric Patterns of Knot Arangements and other Cryptographic Methods on the Surfaces of Ancient Tiles (Kashis) and its Adaptation to Three-Dimensional Arrangement of Atoms in Crystalline Solids

Investigation of Two-Dimensional Geometric Patterns of Knot Arangements and other Cryptographic Methods on the Surfaces of Ancient Tiles (Kashis) and its Adaptation to Three-Dimensional Arrangement of Atoms in Crystalline Solids

Effect of Cu on the strengthening and embrittling of an FeCoNiCr-xCu HEA

The effect of Cu concentration on the microstructure and mechanical properties of FeCoNiCr- x Cu HEAs was investigated. The results showed that low Cu concentrations (less than ∼5 at. %) contributed to a solid solution strengthening effect. The solid solution Cu atom strengthened the yield strength and ultimate tensile strength together. When the Cu concentration reached approximately 7 at. %, larger numbers of nano Cu-rich particle precipitated from the FCC matrix. The nano Cu-rich particle had a strengthening effect and further increased the yield strength and ultimate tensile strength. When the Cu concentration reached approximately 13 at. %, the weak continuous Cu-rich phase formed between dendrites. The early fracture of the Cu-rich phase dramatically decreased the ultimate tensile strength and elongation.

Trapping and migration of P-state atoms in rare gas solids: effect of angular momentum anisotropy for model O(3P) and C(3P) atoms

Classical simulations of model O(P) atom isolated in Ar, Kr and Xe crystals with the variable magnitude and sign of the angular momentum anisotropy are performed. The guest–host interaction anisotropy remarkably affects the structure of the atomic trapping sites and the barriers to the temperature-induced atomic mobility. For interstitial trapping, inversion of anisotropy induces a kind of critical phenomenon, which transforms the migration path saddle point to a minimum and another saddle. As a result, a new peculiar axially symmetric interstitial site is formed with the migration barrier reduced. Preliminary ab initio-based study of the C(P) atom, whose interactions with Ar, Kr and Xe have the anisotropy opposite to oxygen, fully confirms the model analysis. Our results emphasise profound effect of the angular momentum anisotropy on the structure and dynamics of the open-shell atoms at matrix isolation.

Electron and positron backscattering from condensed targets

The backscattering process for electron and positron impinging on condensed targets is studied here. The calculation is performed for Li, Na, Al and Cu atoms in the 500–3000 eV energy range. The well known Vicanek and Urbassek theory is used to determine the backscattering coefficient for present solid atoms. To analyze the elastic scattering cross section, spherical complex optical potential formalism is used. Apart from the backscattering coefficient, momentum transfer cross section, range of penetration, and mean number of wide-angle collisions are also tabulated and compared to the available data. No previous work was found reporting the range of penetration for the atoms. Hence, we also report the electron backscattering coefficient and range of penetration for liquid water for which experimental and theoretical data are available for the range of penetration. The electron backscattering coefficient for liquid water is reported for the first time here.

Effect of in-situ Al2O3 on tensile strength and ductility of AlSi10Mg alloy fabricated by selective laser melting

The in-situ Al2O3 modified AlSi10Mg alloy was fabricated by selective laser melting using AlSi10Mg/ZnO mixed powders. The results show that the aluminothermic reaction between the Al and ZnO occurs when the laser fuses the AlSi10Mg/ZnO mixed powders. This leads to the in-situ formation of Zn and Al2O3 nanoparticles in the AlSi10Mg alloy. The Zn can exist in the Al matrix as solid solution atoms. The effect of Zn on the tensile strength and ductility of the AlSi10Mg alloy is rather limited. However, the in-situ Al2O3 impedes the motion of dislocations and thus improves the strength of the AlSi10Mg alloy. Moreover, the dislocations accumulated around the in-situ Al2O3 are gradually annihilated along the Al/Si boundaries. Thus the ductility of the AlSi10Mg alloy is scarcely affected by the in-situ Al2O3.

Effect of Carbon Content on Microstructure, Properties and Texture of Ultra-Thin Hot Rolled Strip Produced by Endless Roll Technology.

In order to make a comprehensive comparison between ultra-thin hot rolled low carbon steel (LC) and extra low carbon steel (ELC) produced by endless roll technology and explain the differences, a detailed investigation into the microstructural characterization, characteristics of cementite and precipitates, mechanical properties, internal friction peaks, texture characterization by an X-ray powder diffractometer and electron backscatter diffraction, and formability including earing behavior, hole expanding ratio and V-shaped bending properties was carried out with different carbon content for 1.0 mm thickness ultra-thin hot rolled strip produced in endless strip production line. The experimental results indicate that the microstructure of both is composed of multi-layer areas with different grain sizes and thicknesses, the strength and elongation of LC are higher than that of ELC, but the content of solid solution carbon atoms and r of ELC are higher than that of LC, at the same time, the formability of ultra-thin strip ELC is better than that of LC mainly related to the content of {hkl} <110> and {111} <112> of ELC was higher than those of LC. The mechanical and formability properties of ultra-thin hot rolled strip by endless roll technology can meet the requirements of replacement cold rolled strip by hot rolled strip.

Head-on Collision of Two Nanodroplets on a Solid Surface: A Molecular Dynamics Simulation Study.

Most researchers focus on the collision of a single droplet with a solid surface, while it is common for a droplet to collide with a sessile droplet on a solid surface in reality. This study performed the head-on collision of two nanodroplets on a solid surface using the molecular dynamics simulation method. The effects of impact velocity, interaction intensity between solid and liquid atoms, and the solid fraction of the surface on the collision process are studied with independent simulation cases. The maximum spreading factor and the dimensionless maximum spreading time are recorded and calculated to describe the collision process quantitatively. The simulation results indicate that the maximum spreading factor depends more on the solid fraction than the interaction intensity since it does not fundamentally change the wetting state of the droplet at its maximum spreading state. Because of two different effects, the maximum dimensionless spreading time decreases first and then increases with the interaction intensity, and both effects weaken with the increase of impact velocity. As the solid fraction increases, the maximum spreading factor increases significantly at high impact velocity, and the maximum dimensionless spreading time first decreases and then increases because the wetting state of the coalescent droplet at the maximum spreading moment gradually changes from the Wenzel state to the Cassie state. In general, the initial wetting state of the sessile droplet and the wetting state of the coalescent droplet at the maximum spreading moment have important effects on the maximum spreading factor and the maximum spreading time. We establish a theoretical prediction model for the maximum spreading factor on a smooth surface based on energy conservation with quite good accuracy. This research has improved our understanding of the head-on collision process of two nanodroplets on a solid surface.

Effect of Cooling Methods on Microstructure and Mechanical Properties of Hot-extruded Cu-15Ni-8Sn Alloy

The effect of cooling method on microstructures and mechanical properties of the hot-extruded Cu-15Ni-8Sn bars were investigated by optical microscope(OM), scanning electronic microscope(SEM), differential scanning calorimetry(DSC) and tensile testing. The results indicated that the content of solid solution atom Sn in the water-cooled alloy after hot extrusion is greater than that in the air-cooled alloy. The precipitation onset temperature and dissolution termination temperature of γ phase in the water-cooled alloy are 24 °C and 32 °C lower than that in the air-cooled alloy, respectively. Both water-cooled and air-cooled alloys are composed of γ phase and supersaturated solid solution α(Cu), and show the similar grain size about 23 μm. In the air-cooled alloy, a large number of dispersed rod-like and granular γ-phases are precipitated in the grains, while only granular γ phase is observed in water-cooled alloy with. The tensile strength, elongation and microhardness of the water-cooled and air-cooled alloys are 588±12 MPa and 855±41 MPa, 41.6±2.0% and 15.2±1.0%, 166±7 HV and 292±5 HV, respectively, while the former shows a typical ductile fracture mechanism and the latter has somewhat brittle fracture characteristics.

A molecular dynamics investigation on the effects of electrostatic forces on nanoscale thin film evaporation

Thin-film evaporation is relevant for electronics cooling, water desalination, and some energy conversion processes, and the overall performance of such applications relies on the adequate understanding of heating-induced phase-change mechanisms. Given the importance of polar compounds, such as alumina, for nanoporous membranes in water desalination, the effects of electrostatic forces on thin-film evaporation were investigated in this paper by means of molecular dynamics simulations. The influence of the electrostatic interactions was assessed by modelling the alumina-water interactions using two approaches: i) accounting for electrostatic and dispersive van der Waals (vdWs) forces between the solid and liquid atoms (LJ+Coulombic model), and ii) considering only dispersive vdWs interactions (LJ model). Additionally, a theoretical model based on the Schrage relationships was developed to compare theory and simulations. The results showed considerable differences in the evaporation rates obtained from the two interfacial models. For the LJ+Coulombic model, the liquid films were 40% thicker, and the maximum evaporation mass flux was lower than the LJ model by a factor of two. The theoretical Schrage relationships deviated from the simulation evaporation fluxes with errors of 2.2-18.1% and 24.0-57.9% for the LJ+Coulombic and LJ models, respectively. These observations suggest that the partial charges in the solid affect the evaporation behavior of water if the films are ∼5 nm or thinner. Moreover, the significant deviations in the evaporation behavior demonstrated the importance of a robust interfacial modelling approach to investigate thin-film evaporation in polar interfaces.

A strategy to regulate the microstructure and properties of Mg-2.0Zn-1.5Mn magnesium alloy by tracing the existence of Mn element

The role of Mn existence types on microstructure and mechanical properties of extruded Mg-2.0Zn-1.5Mn magnesium alloy is investigated. Four different Mn existence types in Mg-2.0Zn-1.5Mn magnesium alloy are obtained by different heat treatment. The four types include: (1) solid solution Mn atoms, (2) nanoscale α-Mn phase, (3) solid solution atoms + micron scale α-Mn phase, (4) micron scale α-Mn phase + nanoscale α-Mn phase, respectively. The result shows pre-existed nanoscale α-Mn particles present good pinning effect for refining grains. The micron scale α-Mn phase activates the particle stimulated nucleation (PSN) mechanism. The combination of micron scale α-Mn phase + nanoscale α-Mn phase state presents the best grain refining effect with an average grain size of 1.3 µm. The mechanical properties are significantly enhanced, the tensile yield strength, tensile strength and fracture elongation are 267 MPa, 305 MPa, 28.6%, respectively. Based on the results, four basic rules for preparing fine grained Mn-containing Mg alloys are proposed and an ideal pre-extrusion state of Mn-containing alloy is obtained: namely, direct extrusion in the as-cast-aging state. Besides has great potential for grain refinement, this state also can be regulated by the coordination of PSN effect and pinning effect in Mn-containing Mg alloy.

Energy-Based Interface Detection for Phase Change Processes of Monatomic Fluids in Nanoconfinements.

An energy-based liquid-vapor interface detection method is presented using molecular dynamics simulations of liquid menisci confined between two parallel plates under equilibrium and evaporation/condensation conditions. This method defines the liquid-vapor interface at the location where the average kinetic energy of atoms first exceeds the average potential energy imposed by all neighboring molecules. This definition naturally adapts to the location of the menisci relative to the walls and can properly model the behavior of the liquid adsorbed layers. Unlike the density cutoff methods frequently used in the literature that suffer from density layering effects, this new method gives smooth and continuous liquid-vapor interfaces in nanoconfinements. Surface tension values calculated from the equilibrium MD simulations match the Young-Laplace equation better when using the radius of curvatures calculated from this method. Overall, this energy-based liquid-vapor interface detection method can be used in studies of nanoscale phase change processes and other relevant applications.

Investigation of the effects of surface wettability and surface roughness on nanoscale boiling process using molecular dynamics simulation

The nanoscale liquid-vapor phase change process of argon above solid copper substrates with different surface wettability and surface roughness are studied with the help of nonequilibrium molecular dynamics simulations. The contact angles of an argon droplet on the copper solid substrate with different potential parameters are determined by the circle fitting function. With a constant temperature thermostat applied on the solid substrate, the liquid argon atoms absorbed energy. It was found that the increase of argon wettability on solid copper surfaces could enhance the heat transfer between the solid and fluid atoms and also the evaporation mass flux of liquid argon. The bubble nucleation time was advanced as well by the increased wettability. Moreover, the effect surface roughness generated using a multivariable Weierstrass-Mandelbrot function on the nanoscale boiling process was also investigated. The rough structures on the substrate could further advance the boiling inception and increase the evaporation rate. The energy transfer between the solid and fluid atoms become more efficient with the surface rough textures.

Effect of Nitrogen on the Hot Deformation Behavior of 0.4C–13Cr Martensitic Stainless Steel

The hot deformation behaviors of 0.4C–13Cr martensitic stainless steel at the nitrogen contents of 0.13% and 0.03%, respectively, are investigated at the deformation condition featuring the temperature range of 1223–1523 K and the strain rate range of 0.01–10 s−1. The variation of flow stress curves of experimental steels with different nitrogen contents is systematically analyzed. According to the flow stress curves, the activation energies determined by regression analysis are 472.77 and 411.58 kJ mol−1 for 0.4C–13Cr steel with N contents of 0.13% and 0.03%, respectively. It demonstrates that the deformation resistance of 0.4C–13Cr steel improves with the increase in nitrogen content. The reason is related to the pinning effect of solid solution nitrogen atoms, and Cr2N particles on dislocations and grain boundaries. The dynamic recrystallization (DRX) kinetics models of experimental steels are established. Furthermore, the microstructures of experimental steels are also analyzed. The result shows that the pinning effect caused by nitrogen also plays an important role in the development of DRX and microstructure evolution. The more nitrogen addition in 0.4C–13Cr steel, the earlier achievement of DRX onset, the slower the DRX kinetics and the finer the microstructure.

Effect of Vanadium on Superhardenability of 23MnNiMoCr54V Steel for Round-Link Chain in Mining Applications

The effect of vanadium on the hardenability and microstructure of 23MnNiMoCr54V steel was investigated after austenitizing at 950 and 1050 °C by dilatometry and end-quenching Jominy tests, combined with nitrogen removal with aluminum. Electron probe micro-analysis, scanning electron microscopy and transmission electron microscopy techniques were used to characterize the microstructure and existence state of vanadium atoms in the steel. The presence of aluminum-stabilized nitrogen by aluminum nitride production, which promoted the segregation of solid solution vanadium atoms at grain boundaries, delayed the transformation of ferrite and improved the austenite stability. Thus, vanadium addition could improve the hardenability, and an excellent steel performance could be obtained during slower cooling. This process could be used to produce heavy section steel components, such as round-link chains for mining applications.

Single atom catalysts by atomic diffusion strategy

The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today. Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants, especially, single-atom catalysts (SACs) are promising candidates. Herein, we comprehensively summarizes the atomic diffusion strategy, which is considered as an effective method to prepare a series of SACs. According to the different diffusion forms of the precursors, we review the synthesis pathways of SACs from three aspects: gas diffusion, solid diffusion and liquid diffusion. The gaseous diffusion method mainly discusses atomic layer deposition (ALD) and chemical vapor deposition (CVD), both of which carry out gas phase mass transfer at high temperatures. The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration. Liquid diffusion mainly describes the electrochemical method and the molten salt method. We hope this review can trigger the rational design of SACs.

Excitations of atomic vibrations in amorphous solids

We study excitations of atomic vibrations in the reciprocal space for amorphous solids. There are two kinds of excitations we obtained, collective excitation and local excitation. The collective excitation is the collective vibration of atoms in the amorphous solids while the local excitation is stimulated locally by a single atom vibrating in the solids. We introduce a continuous wave vector for the study and transform the equations of atomic vibrations from the real space to the reciprocal space. We take the amorphous silicon as an example and calculate the structures of the excitations in the reciprocal space. Results show that an excitation is a wave packet composed of a collection of plane waves. We also find a periodical structure in the reciprocal space for the collective excitation with longitudinal vibrations, which is originated from the local order of the structure in the real space of the amorphous solid. For the local excitation, the wave vector is complex. The imaginary part of the wave vector is inversed to evaluate the decaying length of the local excitation. It is found that the decaying length is larger for the local excitation with a higher vibration frequency.

A bioinspired Au-Cu1.97S/Cu2S film with efficient low-angle-dependent and thermal-assisted photodetection properties

SummaryInspired by the geological processes, this study develops an innovative low-concentration-ratio H2 reduction method to reduce the stoichiometric Au-CuS nanoparticles to produce completely reduced stoichiometric Cu2S with “invisible” Au achieved for solid solution Au enhancement. A stable Au-Cu1.97S/Cu2S micro/nano-composite is then formed by spontaneous oxidation. From this composite, in combination with biomimetic technology, an omnidirectional photoabsorption and thermoregulated film (Au-Cu1.97S/Cu2S-C-T_FW) is designed and fabricated as a photothermal-assisted and temperature-autoregulated photodetector for broadband and low-angle-dependent photodetection that presents good performance with high responsivity (26.37 mA/W), detectivity (1.25×108 Jones), and good stability at low bias (0.5 V). Solid solution Au exhibits significantly enhanced photodetection (1,000 times). This study offers a new concept for improving the stability and photoelectric properties of copper chalcogenides. Moreover, it opens up a new avenue toward enhancing the performance of optoelectronic and photovoltaic devices using solid solution metal atoms and thermal-assisted, anti-overheating temperature autoregulation.

Damage to Relativistic Interstellar Spacecraft by ISM Impact Gas Accumulation

Abstract As part of the NASA Starlight collaboration, we look at the implications of impacts with the interstellar medium (ISM) on a directed energy-driven relativistic spacecraft. The spacecraft experiences a stream of MeV/nucleon impacts along the forward edge primarily from hydrogen and helium nuclei. The accumulation of implanted slowly diffusing gas atoms in solids drives damage through the meso-scale processes of bubble formation, blistering, and exfoliation. This results in macroscopic changes to material properties and, in the cases of blistering and exfoliation, material erosion via blister rupture and delamination. Relativistic hydrogen and helium at constant velocity will stop in the material at a similar depth, as predicted by Bethe–Bloch stopping and subsequent simulations of the implantation distribution, leading to a mixed hydrogen and helium system similar to that observed within fusion plasma-facing components. However, the difference in depth of near-surface gas atoms with respect to the direction of exposure means that previously developed empirical models of blistering cannot be used to predict bubble formation or blistering onset. In this work, we present a model of the local gas concentration threshold for material blistering from exposure to the ISM at relativistic speeds. Expected effects on the spacecraft and mitigation strategies are also discussed. The same considerations apply to the Breakthrough Starshot mission.

Strengthening Mechanism of Low Cycle Fatigue Resistance for Cr-Mo Tempered Martensite Steel at 350 °C

In the process of fatigue loading, the segregation of solid solution elements makes dislocations continuously pile-up in ferrite lath to form subgrain, which improves the fatigue properties. In this study, the low cycle fatigue properties of two kinds of Cr-Mo tempered martensitic steels with different grain sizes were investigated at 350 °C. Then, the fracture morphology and the subgrain of ferrite lath were analyzed. The results show that the low cycle fatigue life of 90H steel is significantly higher than that of 80H steel, and a large number of secondary cracks are found in the fatigue fracture. The reason is that the segregation of solid solution atoms affects the dislocations movement during low cycle fatigue. And the finer lath subgrain structure of 90H steel makes it easier to occur in grain. Thus, the evolution process of subgrain structures is changed, and the crack propagation is hindered, resulting in a large number of secondary cracks, which improves the fatigue life. In addition, the segregation effect on fatigue life decreased with the strain amplitude increasing.

A Study on the Damping Capacities of Mg–Zn–Y-Based Alloys with Lamellar Long Period Stacking Ordered Phases by Preparation Process

Mg alloys with fine mechanical properties and high damping capacities are essential in engineering applications. In this work, Mg–Zn–Y based alloys with lamellar long period stacking ordered (LPSO) phases were obtained by different processes. The results show that a more lamellar second phase can be obtained in the samples with more solid solution atoms. The density of the lamellar LPSO phase has an obvious effect on the damping of the magnesium alloy. The compact LPSO phase is not conducive to dislocation damping, but sparse lamellar phases can improve the damping capacity without significantly reducing the mechanical properties. The Mg95.3Zn2Y2.7 alloy with lamellar LPSO phases and ~100 μm grain size exhibited a fine damping property of 0.110 at ε = 10–3.