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The manufacturing process for wrought Ti alloys with the hexagonal close-packed (HCP) structure introduces a complicated microstructure with abundant intra- and inter-grain boundaries, which greatly influence performance. In the hexagonal close-packed (HCP) structure, two types of grain boundaries are commonly observed between grains with ~90° misorientation: the basal/prismatic boundary (BPB) and the coherent twin boundary (CTB). The mechanical response of the BPB and CTB under external loading was studied through molecular dynamic simulations of HCP-Ti. The results revealed that CTB undergoes transformation into BPB through the accumulation of twin boundary (TB) steps and subsequent emission of Shockley partial dislocations. When the total mismatch vector is close to the Burgers vector of a Shockley partial dislocation, BPB emits partial dislocations and further grows along the stacking faults. When a pair of CTBs are close to each other, severe boundary distortion occurs, facilitating the emission and absorption of partial dislocations, which further assists the CTB-BPB transformation. The present results thus help to explain the frequent observation of coexisting CTB and BPB in HCP alloys and further contribute to the understanding of their microstructure and property regulation. [ABSTRACT FROM AUTHOR]

The preparation of glass–ceramics with red mud and steel slag can not only solve the pollution problem caused by industrial waste slag but also produce economic benefits. It is difficult to analyze the high-temperature melt with the existing test methods, so the simulation experiment with molecular dynamics calculation becomes an important research method. The effects of steel slag content on the microstructure of red mud glass–ceramics were studied by molecular dynamics method. The results show that the binding ability of Si-O, Al-O, and Fe-O decreases with the increase in steel slag content. The number of Si-O-Si bridge oxygen increased gradually, while the number of Al-O-Al, Al-O-Fe, and Fe-O-Fe bridge oxygen decreased significantly. The number of tetrahedrons [SiO4] increased, the number of tetrahedrons [FeO4] and [AlO4] decreased, and the total number of three tetrahedrons decreased. The mean square displacement value of Si4+ and O2− increases first and then decreases, resulting in the viscosity of the system decreasing first and then increasing. The molecular dynamics method is used to analyze the structure of red mud–steel slag glass–ceramics on the microscopic scale, which can better understand the role of steel slag and has guiding significance for the experiment of this kind of glass–ceramics. [ABSTRACT FROM AUTHOR]

As a subclass of the biopharmaceutical classification system (BCS) class II, basic drugs (BCS IIB) exhibit pH-dependent solubility and tend to generate supersaturation in the gastrointestinal tract, leading to less qualified in vitro–in vivo correlation (IVIVC). This study aims to develop a physiologically based multi-cup dissolution approach to improve the evaluation of the supersaturation for a higher quality of IVIVC and preliminarily explores the molecular mechanism of supersaturation and precipitation of ketoconazole affected by Polyvinylpyrrolidone–vinyl acetate copolymer (PVPVA) and hydroxypropyl methyl-cellulose (HPMC). The concentration of ketoconazole in each cup of the dynamic gastrointestinal model (DGIM) was measured using fiber optical probes. Molecular interactions between ketoconazole and PVPVA or HPMC were simulated by Materials Studio. The results demonstrated that PVPVA and HPMC improved and maintained the supersaturation of ketoconazole. PVPVA exhibited superior precipitation inhibitory effect on ketoconazole molecule aggregation due to slightly stronger van der Waals forces as well as unique electrostatic forces, thereby further enhancing in vitro drug absorption, which correlated well with in vivo drug absorption. Compared with a conventional dissolution apparatus paddle method, the DGIM improved the mean prediction error through the IVIVC from 19.30% to 9.96%, reaching the qualification criteria. In conclusion, the physiologically based multi-cup dissolution approach enables improved evaluation of supersaturation in gastrointestinal transportation of BCS IIB drug ketoconazole, enabling screening screen precipitation inhibitors and achieving qualified IVIVC for drug formulation studies. [ABSTRACT FROM AUTHOR]

Methazolamide is a carbonic anhydrase (CA) inhibitor with satisfactory safety. Our previous studies have demonstrated the elevation of CA1 expression and the therapeutic effect of Methazolamide in Ankylosing spondylitis (AS). In this study, we explored the pathogenic role of CA1 and the pharmacological mechanism of Methazolamide in AS through Gene Set Enrichment Analysis (GSEA) and network pharmacology. Seven out of twelve CA1 related gene sets were enriched in AS group. CA1 was core enriched in above seven gene sets involving zinc ion binding, arylesterase activity and one carbon metabolic process. Functional analysis of the candidate target genes obtained from the intersection of AS associated genes and Methazolamide target genes indicated that Methazolamide exerts therapeutic effects on AS mainly through inflammatory pathways which regulate the production of tumor necrosis factor, IL-6 and nitric oxide. PTGS2, ESR1, GSK3β, JAK2, NOS2 and CA1 were selected as therapeutic targets of Methazolamide in AS. Molecular docking and molecular dynamics simulations were performed successfully. In addition, we innovatively obtained the intersection of Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses and GSEA results, and found that 18 GO terms and 5 KEGG terms were indicated in the pharmacological mechanism of Methazolamide in AS, involving bone mineralization, angiogenesis, inflammation, and chemokine signaling pathways. Nevertheless, validation for these mechanisms is needed in vivo/vitro experiments. [ABSTRACT FROM AUTHOR]

The interface between explosive crystal and binder polymer plays a critical role in the stabilities of energetic materials. In the present work, we investigate the mechanical properties of cyclotetramethylenetetranitramine (HMX)–polystyrene (PS) interface by performing molecular dynamics simulations of uniaxial tension, nanoindentation and nanoscratching tests. Our simulation results indicate that the HMX–PS interface has a mediate strength between HMX of high strength and PS of low strength. In particular for nanoindentation and nanoscratching, the distance of indentation position or scratching position to the HMX–PS interface has a strong influence on mechanical deformation behavior of HMX–PS system. Specifically, the HMX–PS interface has the lowest indentation force and scratching force than both the HMX and the PS. [ABSTRACT FROM AUTHOR]

The ultra-precision diamond cutting process exhibits strong size effects due to the ultra-small depth of cut that is comparable with the cutting edge radius. In the present work, we elucidate the underlying machining mechanisms of single crystal cerium under diamond cutting by means of molecular dynamics simulations, with an emphasis on the evaluation of the effect of depth of cut on the cutting process by using different depths of cut. Diamond cutting experiments of cerium with different depths of cut are also conducted. In particular for the smallest depth of cut of 0.2 nm, shallow cutting simulations varying the sharpness of the cutting edge demonstrate that an atomically sharp cutting edge leads to a smaller machining force and better machined surface quality than a blunt one. Simulation results indicate that dislocation slip is the dominant deformation mechanism of cerium under diamond cutting with each depth of cut. Furthermore, the analysis of the defect zone based on atomic radial distribution functions demonstrates that there are trivial phase transformations from γ-Ce to δ-Ce occurred in both the machined surface and the formed chip. It is found that there is a transition of material removal mode from plowing to cutting with the increase of the depth of cut, which is also consistent with the diamond cutting experiments of cerium with different depths of cut. [ABSTRACT FROM AUTHOR]

The coupling between structural phase transformations and dislocations induces challenges in understanding the deformation behavior of metallic cerium at the nanoscale. In the present work, we elucidate the underlying mechanism of cerium under ultra-precision diamond cutting by means of molecular dynamics modeling and simulations. The molecular dynamics model of diamond cutting of cerium is established by assigning empirical potentials to describe atomic interactions and evaluating properties of two face-centered cubic cerium phases. Subsequent molecular dynamics simulations reveal that dislocation slip dominates the plastic deformation of cerium under the cutting process. In addition, the analysis based on atomic radial distribution functions demonstrates that there are trivial phase transformations from the γ-Ce to the δ-Ce occurred in both machined surface and formed chip. Following investigations on machining parameter dependence reveal the optimal machining conditions for achieving high quality of machined surface of cerium. [ABSTRACT FROM AUTHOR]

In the present work, we perform experiments and molecular dynamics simulations to elucidate the underlying deformation mechanisms of single crystalline copper under the load-controlled multi-passes nanoscratching using a triangular pyramidal probe. The correlation of microscopic deformation behavior of the material with macroscopically-observed machining results is revealed. Moreover, the influence of crystallographic orientation on the nanoscratching of single crystalline copper is examined. Our simulation results indicate that the plastic deformation of single crystalline Cu under the nanoscratching is exclusively governed by dislocation mechanisms. However, there is no glissile dislocation structure formed due to the probe oscillation under the load-controlled mode. Both experiments and MD simulations demonstrate that the machined surface morphologies in terms of groove depth and surface pile-up exhibit strong crystallographic orientation dependence, because of different geometries of activated slip planes cutting with free surfaces and strain hardening abilities associated with different crystallographic orientations. [ABSTRACT FROM AUTHOR]

In current study molecular dynamics (MD) simulations are performed to reveal effects of pre-existing defects on nanoimprint of single crystal aluminum () thin films. Simulation results suggest that critical force required for plastic deformation initiation decreases with the increase of vacancy volume fraction, but increases with the interstitial volume fraction. It is found that adsorption phenomenon is affected by pre-existing defects, as adsorption phenomenon weakens with the increasing interstitial volume fraction. Pre-existing defects have significant influence on the deformation mechanisms and imprint forces during the nanoimprint processes. Simulation results also show that surface deformation is strongly affected by pre-existing defects. [ABSTRACT FROM AUTHOR]

Abstract: AFM is a powerful and versatile tool which has the ability to fabricate nanoelectronics and other nanoparts using nano-scratching method. To achieve a deeper understanding on AFM-based nano-scratching process, molecular dynamic (MD) simulation approach is employed. Interactive forces between a rigid pyramidal tool simulating an AFM diamond tip and a copper sample are modeled by the Morse function. Two adjacent scratching tests are carried out at different feeds simulating the multiple scratching tests. Effects of the feed on the scratching process are discussed. Results show that the feed has a significant effect on the deformation of the machined surface, the scratching depth, scratching forces and potential energy. The important effect of the relax process in the MD simulation of AFM-based multiple nano-scratching processes is exhibited, which cannot be ignored when analyzing the variation of the potential energy. [Copyright &y& Elsevier]

Understanding the hydrodynamic properties of polymeric coatings is crucial for the rational design of molecular transport involving polymeric surfaces and is relevant to drug delivery, sieving, molecular separations, etc. It has been found that the hydrodynamic radius of a polymer segment is an order of magnitude smaller than its physical size, but the origin of this effect does not seem to be well understood. Herein, we study the hydrodynamic properties of polymeric coatings by using molecular dynamics simulations, navigated by the continuous Navier-Stokes-Brinkman model. We confirm that the averaged hydrodynamic radius of a polymer bead is about one order of magnitude smaller than its physical radius, and, in addition, we show that it exhibits a strong dependence on the degree of polymerization. We relate this variation of the hydrodynamic radius to the structural properties and hydrodynamic shielding by surrounding polymer beads. This is done by separating the effects originating from near and far beads. For the near beads, shielding is mainly due to the two nearest beads (of the same polymer) and leads to about a 5-fold reduction in the hydrodynamic radius. Assuming the additivity of the hydrodynamic shielding by far beads, we suggest a simple model, which captures correctly the qualitative behaviour of the hydrodynamic radius with the degree of polymerization. The revealed shielding effects provide important insights relevant to the advanced modelling of hydrodynamic properties of polymeric coatings. [ABSTRACT FROM AUTHOR]

The high chemical inertness of silicon carbide (SiC) makes it difficult for surface chemical reactions to occur. Surface oxidation reactions are crucial for improving the processing efficiency and surface quality of SiC wafers. Extensive research has been conducted on conventional aqueous polishing slurries, while investigations on non-aqueous solvent-based polishing slurries have emerged as alternative options for enhancing SiC surface processing, as evidenced by recent scholarly reports. However, the surface chemical reaction mechanism of silicon carbide in either water or other hydroxyl groups containing solvents remains still unclear and is not well understood. In this work, ReaxFF molecular dynamics simulation was used to study the dynamic reaction processes between solvents and 6H SiC (001) surfaces. The oxidation of SiC surface in water and alcohol solvent is found to go through three stages: in the first stage, the solvent molecules move towards the SiC surface and react with the uncoordinated Si atoms and C atoms on the surface; in the second stage, the solvent molecules adsorbed on the surface of SiC reduces the Si –C bonding energy and promotes the breaking of Si –C bonds; in the third final stage, the migration of OH and H on the SiC surface induces the formation of Si – O –Si bonds, which promotes the continuous oxidation of the SiC surface. The order of simulated chemical reactivity between solvent and silicon carbide surface is consistent with experimental polishing removal rates. The reaction mechanism of solvent on silicon carbide surface was proposed by combining ReaxFF simulation results with polishing experiments, AFM, and XPS data analysis, shedding new insights on better understanding the mechanism of SiC chemical mechanical polishing. [ABSTRACT FROM AUTHOR]

Machined surface quality in terms of residual stress and surface roughness has an important influence on the performance of devices and components. In the present work, we elucidate the formation mechanisms of residual stress and surface roughness of single crystalline cerium under ultraprecision diamond cutting by means of molecular dynamics simulations. Influences of machining parameters, such as the rake angle of a cutting tool, depth of cut, and crystal orientation of the workpiece on the machined surface quality were also investigated. Simulation results revealed that dislocation activity and lattice distortion are the two parallel factors that govern the formation of both residual stress and surface roughness. It was found that both distributions of residual stress and surface roughness of machined surface are significantly affected by machining parameters. The optimum machining parameters for achieving high machined surface quality of cerium by diamond cutting are revealed. [ABSTRACT FROM AUTHOR]

The machinability of hard brittle polycrystalline ceramic has a strong correlation with internal microstructures and their accommodated deformation behavior. In the present work, we investigate the mechanisms governing the brittle-to-ductile transition behavior of polycrystalline 3C–SiC in diamond cutting by means of molecular dynamics simulations. Simulation results reveal the co-existence of dislocation slip and amorphization-dominated ductile deformation and cracking along grain boundaries-mediated brittle fracture, as well as the correlation of individual deformation modes with machining force variation and machined surface morphology. In addition, inter-granular fracture, grain boundary sliding and grain pull-up are also operating brittle deformation modes of polycrystalline 3C–SiC. The strong competition between above heterogeneous deformation modes determines the brittle-to-ductile transition behavior in grooving of polycrystalline 3C–SiC. Simulation results also demonstrate that grain size has a strong impact on the brittle-to-ductile transition and material deformation behavior of polycrystalline 3C–SiC under diamond cutting. [ABSTRACT FROM AUTHOR]

Precision polishing of mono-crystalline SiC wafers on a fixed abrasive pad is investigated by double-nano-abrasives cutting at micro/nano scale in this report. Prior to this report, a single abrasive approach in molecular dynamics simulation had been employed to illustrate the material removal mechanism in SiC polishing process, which is quite different from the real situation of the fixed abrasive polishing process. Cutting depth and spacing of abrasive particles in a fixed abrasive pads were tested to gain insights on phase transformation, subsurface damage, surface quality, material removal and friction characteristics of polished SiC wafers by molecular dynamics simulation. By following the coordination number and radial distribution function, we clearly see that the number of phase transformation atoms caused by cutting and abrasion increases with the cutting depth of nano-abrasives on the surface of SiC workpiece. Simulation results also suggest that t he phase transformation of the SiC crystal phase increases with the lateral spacing of abrasive particles in pads, while does not change much with the increase of the longitudinal spacing. It is also found that the deeper the abrasive cutting depth, the deeper subsurface damage, resulting more materials' removal from SiC workpiece. The lateral and longitudinal abrasive spacings lead to little change the depth of subsurface damage on the wafer in MD simulation for a fixed double abrasive polishing. The surface roughness is better with the larger lateral abrasive spacing, but no clear correlation with the longitudinal abrasive spacing. [ABSTRACT FROM AUTHOR]

Structural phase transformation and dislocation slip are two important deformation modes of monocrystalline silicon. In the present work, we elucidate mechanisms of inhomogeneous elastic-plastic transition in spherical nanoindentation of monocrystalline silicon by means of molecular dynamics simulations. The Stillinger-Weber potential is utilized to present simultaneous phase transformations and dislocation activities in the silicon nanoindentation. And a bond angle analysis-based method is proposed to quantitatively clarify silicon phases. The influence of crystallographic orientation on the silicon nanoindentation is further addressed. Our simulation results indicate that prior to the “Pop-In” event, Si(0 1 0) undergoes inelastic deformation accompanied by the phase transformation from the Si-I to the Si-III/Si-XII, which is not occurred in Si(1 1 0) and Si(1 1 1). While the phase transformation from the Si-I to the bct-5 is the dominant mechanism of incipient plasticity for each crystallographic orientation, dislocation nucleation is also an operating deformation mode in the elastic-plastic transition of Si(0 1 0). Furthermore, interactions between phase transformations and dislocations are more pronounced in Si(0 1 0) than the other two crystallographic orientations. [ABSTRACT FROM AUTHOR]

The transition of material removal mode of polycrystalline 3C-SiC cutting with temperature, i.e., from brittle mode cutting that is dominated by inter-granular fracture and grain pulling-out at low temperature to ductile mode cutting that is governed by intra-granular cracking and dislocation slip. [Display omitted] • Temperature-dependent mechanical properties of both grains and GBs in polycrystalline 3C-SiC at elevated temperatures are derived. • Temperature-dependent properties of 3C-SiC GBs are bridged between MD simulation and FE simulation with cohesive zone model. • There is transition from brittle mode by inter-granular fracture toductile mode by intra-granular cracking with temperature. While the deformation behavior of grain boundaries has a strong impact on the mechanical response of polycrystalline materials, investigating the coupled thermal–mechanical properties of grain boundaries in their real formats is crucial for enhancing the ductile machinability of hard brittle polycrystalline ceramic materials. In the present work, we report the thermal softening-suppressed inter-granular fracture, accompanied with enhanced stacking fault formation, increased healing ability of grain boundaries and promoted ductile material removal, in diamond cutting of polycrystalline 3C-SiC at elevated temperatures by multi-scale simulations. Molecular dynamics simulations and experiments of high temperature nanoindentations are performed to derive the temperature-dependent mechanical properties of bulk polycrystalline 3C-SiC. Furthermore, molecular dynamics simulations of Mode I (tension) and Mode II (shearing) loading of a Σ9<1 1 0>{1 2 2} symmetric tilt grain boundary at elevated temperatures are performed to extract the temperature-dependent mechanical properties of grain boundaries in polycrystalline 3C-SiC. A novel finite element model of heat treatment-assisted diamond cutting of polycrystalline 3C-SiC with the comprehensive consideration of thermal properties of both grains and grain boundaries at elevated temperatures is established to reveal the transition of material removal mode, grain boundary failure behavior, cutting force characteristics and chip profile with temperature. [ABSTRACT FROM AUTHOR]

In this work, molecular dynamic (MD) simulation is employed to investigate the formation and evolution of amorphous carbons in the surface layer of diamond crystal as the frictional sliding is performed on diamond (1 0 0) plane. Simulation results reveal that the formation of amorphous carbons at the sliding interface is inevitable due to the friction. In this case, transformation from diamond sp 3 hybridized carbons to sp 2 hybridization structures is dominant. More interestingly, most of the sp hybridized carbons appear on the topmost surface of the amorphous layer. Amorphization rate in sliding along the [1 0 0] direction is greater than that along the [1 1 0] direction due to the smaller resistance forces. In the light of the velocity variation of carbon atoms, the amorphous layer is divided into two layers, i.e. the coherent layer and transition layer. Moreover, a density transition region appears with the formation of amorphous carbons, and the thickness of transition region can be used to characterize the amorphization degree. [ABSTRACT FROM AUTHOR]