Microstructural ordering of nanofibers in flow-directed assembly

Fabrication of highly ordered and dense nanofibers assemblies is of key importance for high-performance and multi-functional material and device applications. In this work, we design an experimental approach in silico, where shear flow and solvent evaporation are applied to tune the alignment, overlap of nanofibers, and density of the assemblies. Microscopic dynamics of the process is probed by dissipative particle dynamics simulations, where hydrodynamic and thermal fluctuation effects are fully modeled. We find that microstructural ordering of the assembled nanofibers can be established within a specific range of the Peclet numbers and evaporation rates, while the properties of nanofibers and their interaction are crucial for the local stacking order. The underlying mechanisms are elucidated by considering the competition between hydrodynamic coupling and thermal fluctuation. Based on these understandings, a practical design of flow channels for nanofiber assembly with promising mechanical performance is outlined.Accepted manuscriptSupporting documentatio

Atomic stiffness for bulk modulus prediction and high-throughput screening of ultraincompressible crystals

Abstract Determining bulk moduli is central to high-throughput screening of ultraincompressible materials. However, existing approaches are either too inaccurate or too expensive for general applications, or they are limited to narrow chemistries. Here we define a microscopic quantity to measure the atomic stiffness for each element in the periodic table. Based on this quantity, we derive an analytic formula for bulk modulus prediction. By analyzing numerous crystals from first-principles calculations, this formula shows superior accuracy, efficiency, universality, and interpretability compared to previous empirical/semiempirical formulae and machine learning models. Directed by our formula predictions and verified by first-principles calculations, 47 ultraincompressible crystals rivaling diamond are identified from over one million material candidates, which extends the family of known ultraincompressible crystals. Finally, treasure maps of possible elemental combinations for ultraincompressible crystals are created from our theory. This theory and insights provide guidelines for designing and discovering ultraincompressible crystals of the future

Data-Driven Discovery and Understanding of Ultrahigh-Modulus Crystals

High-modulus materials that yield small elastic deformation under mechanical loads hold great promise for use in a wide range of engineering applications. However, the discovery and understanding of high-modulus materials remain a long-term challenge, as the traditional experimental trial-and-error approach is time-consuming. In this work, we discovered two new ultrahigh-modulus crystals (CN2 and OsN2), exhibiting a maximum Young's modulus (1555.3 and 1382.7 GPa, respectively) greater than that of diamond (1152.0 GPa in our calculations), by data mining of 13 122 crystals and first-principles verifications. More surprisingly, the density of CN2 is lower than that of diamond, which endows it with high modulus and light weight. Furthermore, we explored the mechanical behaviors of the discovered ultrahigh-modulus crystals by performing tensile tests and found that CN2 and OsN2 also boast high strength while maintaining decent ductility. The underlying mechanism for the ultrahigh modulus of these two crystals was explained by analyses of the electron density and bond order. To further broaden our understanding, a data-driven analysis was conducted to quantify the structure-modulus correlations of 10 903 crystals, and six crucial structural and compositional features that are highly correlated to the maximum Young's moduli of crystals were identified. Based on these six features, a nonlinear classifier was developed, which successfully predicted crystals possessing a maximum Young's modulus greater than 1000 GPa and separated them from the others, making this approach useful for falsifiable prediction and discovery of high-modulus crystals. Based on this understanding, suggestions were made to guide the design and synthesis of high-modulus crystals. Additionally, the formation and stabilities of CN2 and OsN2 were explored for practical applications

Superflexible C-68-graphyne as a promising anode material for lithium-ion batteries

The breakthrough in the synthesis of graphyne, graphdiyne and graph-4-yne stimulates interest in studying new members of the graphyne family for promising applications. In this work, a new allotrope of graphyne with excellent stability and an ultrahigh specific surface area of 4255 m(2) g(-1), named C-68-graphyne, is predicted by first principles calculations. Mechanical tests reveal that C-68-graphyne exhibits much smaller in-plane tensile stiffness (similar to 50.5 N m(-1)) and out-of-plane bending stiffness (similar to 0.5 eV) than graphene (in-plane tensile stiffness 350 N m(-1) and out-of-plane bending stiffness 1.4 eV), suggesting C-68-graphyne as a superflexible material. Meanwhile, our results show that monolayer C-68-graphyne is a semiconductor with a direct band gap of 1.0 eV, which can be tuned by strain-engineering, and the calculated carrier mobility is as high as 1.81 x 10(5) to 2.97 x 10(5) cm(2) V-1 s(-1) at 300 K. Finally, the potential application of C-68-graphyne as an anode material for lithium-ion batteries is explored and predicted. The calculated results show highly efficient charge transfer from the adsorbed Li ions to C-68-graphyne yet a low diffusion barrier for Li ions in C-68-graphyne for fast charge/discharge rates. The storage capacities for Li in monolayer and bilayer C-68-graphyne are calculated to be as high as 1954 and 1675 mA h g(-1), respectively. These features make C-68-graphyne a promising anode material for lithium-ion batteries with excellent energy storage capacities as well as fast charge/discharge rates

Rapid fabrication of TiN/AISI 420 stainless steel composite by selective laser melting additive manufacturing

Although metal matrix composites (MMCs) possess high mechanical properties for wide potential applications, there are limited kinds of ex-situ MMCs fabricated via selective laser melting (SLM) until now. In this study, TiN/AISI 420 stainless steel (SS) MMCs samples were fabricated by SLM. Densification behavior, microstructure, hardness and wear performance were investigated with different TiN contents and laser powers. It was found that the addition of TiN has a strong influence on density, which was mainly attributed to its impact on laser absorptivity of powder and wettability of liquid metal. With a higher laser power, the diffusion behavior of TiN became stronger and the densification of composites was improved with a maximum relative density of 98.2%. Both of the distribution and solid-solution of TiN particles were investigated by SEM, XRD and EDS results. The optimized composites achieved a high hardness of HRC 56.7, which is 11.8% higher than that of SLMed pure AISI 420 SS. The wear performance was enhanced due to the improved hardness and TiN reinforcement particle