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The impacting phenomenon of nanodroplets has received much attention due to their importance in various industrial applications. The oblique impingement of single droplets is well understood; however, the effect of oblique angle on impacting the dynamics of multiple droplets at the nanoscale is very limited. To address this gap, we perform molecular dynamics (MD) simulations to study the impacting dynamics of binary nanodroplets with various oblique angles (αob) and Weber numbers (We). Using MD simulations, we directly capture the detailed morphological evolution of the impacting binary droplets with various given conditions. Compared to the oblique impingement of a single droplet, the evolution of impacting binary droplets involves two novel dynamic characteristics: the asymmetric dynamics with droplet preferential spreading in the y direction and the rotating of the coalescing droplet. The mechanisms underlying are well studied. The asymmetric dynamics is a result of the velocity gradient of the outer edge of the spreading droplet, and the rotating effect is due to the change in angular momentum induced by surface force. The analysis and study of these phenomena have never been mentioned in previous studies of single droplet. Finally, we investigate the effect of αob and We on normalized moving distance (L/Dsin) and contact time (tc). This work paves the way for offering a comprehensive understanding of the oblique impingement of binary nanodroplets. [ABSTRACT FROM AUTHOR]

• Microstructure effects on nanoscratch behaviors of gold-platinum alloy are revealed. • Hardness and surface quality tend to improve in the [ 1 1 ¯ 0 ] (111) orientation. • Twinning boundary greatly strengthens the plasticity by promoting dislocation nucleation. • Grain boundary or twinning boundary migration contributes to the high removal rate. The microstructural effect on the mechanical behaviors of gold-platinum alloys during nanoscratch is revealed. By adjusting the microstructures (crystallographic orientation, interface type, grain size, twinning thickness), the hardness, plasticity, removal rate and surface roughness of the alloys are significantly improved. The nanoscratch is performed by molecular dynamics (MD). For the single-crystal (SC) alloys, the [ 1 1 ¯ 0 ] (111) -oriented SC alloy shows the high hardness, wear resistance and low roughness. The high dislocation density induces the strong work hardening while the horizontal twinning boundaries (HTBs) effectively improve the surface quality by hindering the elastic recovery. For the bi-crystal (BC) alloys, the BC alloy with TB exhibits the excellent plasticity and low roughness. TB can uniformly limit the dislocation slip and promote the dislocation nucleation to strengthen the plasticity and surface quality. For the polycrystal (PC) and nanotwinned-polycrystal (NTPC) alloys, the alloys with small grain size or small twinning thickness show the high removal rate and low roughness. The reduction in grain size or twinning thickness inhibits the dislocation motion and promotes the GB or TB migration to improve the surface quality and atomic removal. These results provide an important theoretical basis for the microstructural design and nanofabrication of gold-platinum alloys with smooth surface and remarkable mechanical property, expanding the application for the bimetallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) attract remarkable attention due to the excellent mechanical performance. However, the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed. Here, using a microstructure-based constitutive model and molecular dynamics (MD) simulation, we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation. Due to the interaction between the dislocation and solution, the high dislocation density in FeCoCrNiCu leads to strong work hardening. Plentiful slip systems are stimulated, leading to the good plasticity of FeCoCrNiCu. The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops. The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a 6 [ 1 ¯ 1 2 ¯ ] and a 6 [ 1 1 ¯ 2 ] , which interact with each other, and then emit along the 〈111〉 slip direction. In addition, the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model, which is identified according to the evolution of the dislocation density and the stress-strain curve. Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu, and improve the strength. Therefore, the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu. These results accelerate the discovery of HEAs with excellent mechanical properties, and provide a valuable reference for the industrial application of HEAs. [ABSTRACT FROM AUTHOR]

Twin boundary (TB) plays an important role on the plastic deformation of high entropy alloy (HEA). The strong effects of TB on the deformation response of HEA are revealed from atomic level based on the defect structure, shear strain and surface morphology, by comparing the nanoindentation behavior of nanotwinned FeNiCrCoCu HEA (nt-HEA) and single-crystal FeNiCrCoCu HEA (single-HEA). The plastic deformation of nt-HEA is mainly dominated by the dislocations slip confined by first twinning layer, the TB migration, the dislocation nucleation at TB and the stacking fault tetrahedron (SFT) formation, while the dislocation loop emission is the main plastic deformation feature of single-HEA. Compared to the case for single-HEA, the nanoindentation induces more dislocations in nt-HEA. The shear strain in nt-HEA mainly distributes in the first twinning layer, due to the obstacle effect of TB. The shear zone is larger in nt-HEA, and the distribution of shear strain on the nt-HEA surface is more symmetric. The nanoindentation generates fewer steps on the nt-HEA surface, and then brings about a relatively smooth surface for nt-HEA. These findings provide an insight into the TB effect on the nanoindentation response of FeNiCrCoCu HEA, and develop the application of nanotwinned HEA systems. [ABSTRACT FROM AUTHOR]

• Mechanical behaviors of AuPt alloys are investigated from atomic level. • Monocrystalline AuPt alloy is susceptible to work hardening at low temperature. • Mechanical properties of AuPt alloy are improved greatly by twining boundary. • Mechanical behavior of nanocrystalline AuPt alloy depends on grain size strongly. AuPt alloys are widely applied in electronics, aerospace, and precision equipment fields. A thorough understanding of the mechanical behavior of AuPt alloys is critical for their potential applications. Here, we leverage molecular dynamics (MD) method to for the first reveal the effects of microstructure and temperature on mechanical behavior of AuPt alloys from atomic level. The nanoindentation of monocrystalline (MC), nanotwinned (NT), and nanocrystalline (NC) AuPt alloys are performed. The results demonstrate that the mechanical properties of the MC AuPt alloy are excellent at 77 K because of dislocation strengthening while poor at high temperature due to amorphous behavior. The introduction of twinning boundary (TB) greatly improves the mechanical properties of AuPt alloy by preventing the stress spread and promoting dislocation activity. The mechanical behavior of NC AuPt alloy is strongly dependent on grain size. With increasing average grain size, the dominant plastic deformation mechanism of NC AuPt alloy changes from GB migration to dislocation motion and then to GB destruction. An appropriate grain size should be selected to inhibit GB migration or GB destruction, thereby achieving the enhancement of NC AuPt alloy through dislocation strengthening. This work provides an important theoretical basis for the subsequent design of AuPt alloys with desirable mechanical performances to extend the application prospects of noble metals. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nanoscale sliding friction behavior on Cu/Ag bilayers is influenced by water film. • Water film aggravates subsurface damage and Cu/Ag interface change. • Water film improves groove surface quality and decreases friction coefficient. • There is a water-film thickness benefiting working performance of bilayers. • This thickness minimizes subsurface damage and optimizes groove surface quality. Nanoscale sliding friction behavior of nanoparticle o n Cu/Ag bilayers influenced by water film is investigated by molecular dynamics (MD) simulation. The results show that the existence of water film aggravates the subsurface damage and the change of Cu/Ag interface microstructure, but improves the quality of groove surface and decreases the friction coefficient. Under the water-assisted sliding, there is a water-film thickness to minimize subsurface damage and friction coefficient, while make best groove surface quality. The results give an insight into the sliding friction mechanism of nanoparticle on Cu/Ag bilayers during dry and water-assisted sliding. Importantly, a meaningful guidance is provided for the amount of water used when the bilayer materials are subjected to nanoparticle sliding, thereby reducing the subsurface damage, inhibiting the change of interface microstructure, and improving the groove surface quality. The study is beneficial to develop the working performance and engineering application of bilayer materials. [ABSTRACT FROM AUTHOR]

By performing three-dimensional molecular dynamics (MD) simulations, the effects of the tool radius, depth of cut and grinding speed are thoroughly studied in terms of the workpiece deformation, material removal, dislocation movement, atomic trajectory, grinding temperature and average grinding force. The strength of ductile/brittle (Al/Si) bilayers is largely enhanced, because the interface can hinder the passage of dislocations. The interface in brittle/ductile (Si/Al) bilayers contributes to its ductility by increasing the movability of dislocations when gliding on it. The brittle to ductile transition of bilayers, which strongly depends on the interface debond energy, has a key role in controlling the dislocation slipping mechanism. The investigation also reveals that a larger tool radius, higher grinding speed or deeper depth of cut results in more chipping volume and higher grinding temperature in both bilayers. At the same machining parameters, the above changes in brittle/ductile (Si/Al) bilayers are more apparent than that in ductile/brittle (Al/Si) bilayers, since Si is stiffer and has a higher yield strength than Al. [ABSTRACT FROM AUTHOR]

A phase diagram is established for understanding all the possible outcomes. [Display omitted] • Investigation of dynamic characteristics of impacting binary nanodroplets on hydrophobic solid surfaces. • The spread dynamics at various intrinsic wettability and Weber numbers are investigated and compared. • A new scaling law of impacting nanodroplets is proposed to predict the β max over a wide range of We. • A phase diagram is established for understanding all the possible outcomes. Droplet impact on hydrophobic solid surfaces holds considerable importance in various industrial applications and remains a prominent subject in both academia and industry. Although the dynamic characteristics of single droplets are relatively well understood, understanding the more critical and complex impact process involving binary droplets at the nanoscale is limited. To address this gap, we employ molecular dynamics (MD) simulations to investigate the dynamic behavior of impacting binary nanodroplets on surfaces ranging from hydrophobic to superhydrophobic. Through our MD simulations, we directly capture detailed dynamic evolutions under various conditions, encompassing primary and secondary spreading followed by depositing or bouncing. Specifically, we focus on the spreading dynamics associated with a maximum spread diameter (β max), which are directly related to various practical applications. Taking the scale effect into consideration, we propose a new scaling law to predict β max for impacting binary nanodroplets. By comprehensively examining all the observed outcomes, we develop a phase diagram to gain comprehensive insights into the impact process of binary droplets. This work contributes to a holistic understanding of how binary droplets behave upon impinging hydrophobic or superhydrophobic surfaces, paving the way for advancements in this field. [ABSTRACT FROM AUTHOR]

Polycrystalline Al workpieces go through a complex surface atom sputtering and surface/subsurface atom diffusion throughout the ion beam machining process that plays a critical role in determining machining quality of optical mirror surfaces. Here, we leverage molecular dynamics method for the first time to reveal the machining mechanism and the polycrystalline effect of aluminum during ion beam sputtering, in term of cascade collision, atom trajectory, sputtering yield, and surface characteristic. Polycrystalline Al presents a significant low potential energy state, leading to milder cascade collision and weaker sputtering effects than monocrystalline Al during ion beam machining. The atom trajectory demonstrates irregular variation as the atom diffusion is blocked by grain boundary (GB) in polycrystalline Al, leading to the relief microstructure and poor surface quality. With incident ions increasing, the GBs are broken and atom diffusion enhancing, as well as lower subsurface defects and better finishing surface quality. The microscopic morphology evolves into gravel microstructure. Simulation results also reveal that atom diffusion will benefit from high ion concentration and low ion energy. Sputtering yield variation is more sensitive to ion energy. To acquiring better finishing surface quality of Al without influencing machining efficiency, ion concentration must be increased while the ion energy needs to be decreased appropriately but a large number of cascading collisions need to be ensured. • The machining mechanism and polycrystalline effect of Al during ion beam sputtering are investigated via molecular dynamics simulation. • Cascade collision is milder in polycrystalline Al, and atom trajectory demonstrates irregular variation as the atom diffusion blocked by grain boundary. • Impeding effect of grain boundaries induces the relief microstructure. With incident ions increasing, the grain boundaries are broken, and the gravel structure dominates the surface morphology. • Lower ion energy and higher ion concentration will benefit atomic diffusion, inducing a better finishing surface roughness. [ABSTRACT FROM AUTHOR]

The α9α10 nicotinic acetylcholine receptor (nAChR) is an effective therapeutic target for neuropathic pain. α-Conotoxin RgIA and Vc1.1 are two well-known peptides blocking α9α10 nAChR potently and selectively, which have been extensively investigated as drug candidates. Several key residues were established in previous experimental research. However, the mechanism of the specific interaction still needs to be elucidated in more detail. In this work, we explored the interaction mechanism between RgIA/Vc1.1 and rat α9α10 nAChR using docking and molecular dynamics (MD) simulations. Energy and network analysis programs were used to reveal key residues responsible for their interaction. Our results indicated that the most critical residues were in accord with previous studies. Importantly, several novel residues, including Tyr95, Trp151 in α9 (+)α10 (−) interface as well as Tyr196, Arg59in α10 (+)α9 (−) interface, were found in our models. Furthermore, we analyzed noncovalent interaction energies between RgIA/Vc1.1 and rat α9α10 nAChR. The results showed that three negatively charged residues (Glu197 in α10 subunit, Asp168 in α9 subunit and Asp205 in α10 subunit) were involved in the interaction between RgIA and rat α9α10 nAChR. In contrast, the interaction between Vc1.1 and rat α9α10 nAChR was mediated by the positively charged residues Arg59, Arg81 in α9 (−) subunit. These findings provided further insights into the molecular mechanisms of interaction between RgIA and Vc1.1 and rat α9α10 nAChR. Image 1 • Key residues comparison between rat α9α10 nAChR with RgIA and Vc1.1, respectively. • Electrostatic interaction is the main contribution to the interaction. • For RgIA, the interaction is mainly mediated by the negative charged binding site Glu197 in α10(-) subunit, Asp168 in α9(-) subunit, and Asp205 in α10(+) subunit. • For Vc1.1, the positive charged residue Arg59, Arg81 in α9(-) subunit are vital residues contributing to the interaction. [ABSTRACT FROM AUTHOR]

The correlation between the generalized stacking fault energy and the strengthening mechanisms of Cr–Fe–Co–Ni high-entropy alloys during uniaxial tensile deformation is investigated using molecular dynamics simulations. An increase in the Cr and Fe content decreases the generalized stacking fault energy, while an opposite trend is observed for the content of Co and Ni. A linear correlation is identified between the unstable stacking fault energy and the yield stress. Alloys with a lower Fe content and higher Co and Ni contents show a higher unstable stacking fault energy, and hence higher yield stress. A high density of Lomer–Cottrell locks or deformation twins leads to higher flow stress. The deformation twins play a more important role in enhancing the flow stress as compared to sessile dislocations. Additionally, high unstable stacking fault energy is required to stabilize the defects formed and contribute to increasing flow stress. For a low unstable stacking fault energy, the plastic deformation progresses at lower stress and a bidirectional defect transformation is observed. The results agree with recent experiments and serve as guidelines for how the composition can be used to enhance the yield strength and the efficiency of strengthening mechanisms in Cr–Fe–Co–Ni high-entropy alloys. [Display omitted] • Low Fe and high Co and Ni contents results in higher yield stress in Cr-Fe-Co-Ni. • Relation between stacking fault energy and strengthening mechanisms is established. • Deformation twins provide higher flow stress than sessile dislocations. • Low unstable stacking fault energy results in a bidirectional defect transformation. [ABSTRACT FROM AUTHOR]