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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]

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]

Structural phase transition is often expected when crystalline substrates with high mechanical strength are processed by diamond abrasion at nanoscale. The structural evolution and formation of 3 C-SiC substrates abraded by diamond were explored using molecular dynamics simulation. The evoluted structures were derived by analyzing bond length, bond angle and coordination changes of SiC and diamond abrasives before and after nano-abrasion. Our simulation results explicitly elucidate the stable, graphene-like two-dimensional (2D) structural evolution and formation from SiC and diamond crystalline. This generolized finding of 2D structural formation from three-dimensional (3D) materials in nano-abrasion may shed light on developing new preparation options to make graphene-like 2D-SiC, which is predicted to be a chemically and mechanically stable semicondcuting material with oustanding opto-electro properties. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were performed to investigate the geometric effect of nanostructured substrates on adsorptive behavior of potassium stearate monolayers. A typical protective coating, diamond-like carbon (DLC), was employed as adsorptive substrates. For the substrates with square grooves, complete penetration of molecules can only occur under large width and small depth. The occurrence of partial penetration would make monolayer atoms away from substrate surfaces and therefore induce weak substrate-molecules interactions. Compared with the square groove bottoms, monolayers are much more strongly adsorbed to the groove concave corners. For substrates with triangle and semi-circle grooves, complete penetrations are achieved in both cases and thus monolayer atoms can interact with the whole groove surface. The effect of substrate morphology on monolayer adsorption would be sufficiently weakened by the decrease of geometric size, and the surface adsorptivity of semi-circle grooves with large radius is similar to that of the smooth surface. The results indicate that the substrates with triangle grooves have better adsorptivity than other morphologies. • Size effect of nanostructured diamond-like carbon substrates on adsorption of potassium stearate monolayers was studied using MD simulation. • Geometric size of surface morphologies and amorphous atomic arrangement will significantly influence the molecular adsorption. • The monolayer-to-substrate adhesion at concave corners is much stronger than other positions within grooves. • Complete penetration of monolayers is achieved in all the morphology sizes for triangle grooves and semi-circle grooves. [ABSTRACT FROM AUTHOR]

Abstract: We introduce a new approach to calculate directly the electric current in Born–Oppenheimer molecular dynamics. In this approach the electric current is computed from the adiabatic variations of the Kohn–Sham eigenstates between consecutive time steps. This conceptually straightforward method is fairly efficient and can be easily implemented into existing electronic structure programs. We test the method in two representative systems: liquid D2O and crystalline MgO. The polarization change and the electric current density computed from the present approach are in excellent agreement with those from the Berry phase method and explicit density functional perturbation theory calculations of Born-effective charges. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations were performed to elucidate the mechanisms of deformation in bi-crystal Al thin films with twin boundaries subjected to the nanoimprint process. The effects of stamp spacing on deformation behavior and the mechanical response of the imprinted material were examined. Simulation results indicated that dislocation activity and dislocation–TB interaction are two plastic deformation modes in bi-crystal Al thin films. The results demonstrated that the stamp spacing has significant influence on the dislocation–TB interaction during the nanoimprint process. [Copyright &y& Elsevier]

Abstract: Pre-existing defects can alter mechanical behavior of materials significantly under applied load. In current study molecular dynamics (MD) simulations are performed to reveal pre-existing void effect on nanoimprint of single crystal Al thin films, such as deformation mechanism and spring back phenomenon. Current simulation results show void acts as strong barrier to dislocation motion, although plastic deformation is dominantly controlled by dislocation activities. It indicates the void volume fraction has strong influence on nanoimprint: the larger the void volume fraction, the smaller the maximum force required for initial dislocation nucleation, and the stronger the interaction between extended dislocation and void. It also demonstrates that there is a critical void volume fraction for minimum spring back, which is resulted from competition between two roles affecting dislocation annihilation. [Copyright &y& Elsevier]

Abstract: Three-dimensional molecular dynamics simulations are performed to investigate the AFM-based nanometric scratching process of monocrystalline copper. The effects of scratching velocities (1, 10, and 100m/s) on the chip pattern, scratching resistance, dislocation movement, and workpiece deformation are studied. The results show that the scratching resistance increases with the increase in scratching velocity. The higher scratching velocity results in larger chip volume and closer chip shape with more amorphous structure. The dislocations move well-regulated for lower velocities (1 and 10m/s) than that for larger one (100m/s). The area of workpiece material deformation region beneath the tool edge decreases with the increase in scratching velocity. [Copyright &y& Elsevier]

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]

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]

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]

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]

Molecular dynamics (MD) simulations were used to provide insights into the influence of nano-scale surface morphology on adsorptive behavior of Potassium stearate molecules on diamond-like carbon (DLC) substrates. Particular focus was given to explain that how the distinctive geometric properties of different surface morphologies affect the equilibrium structures and substrate-molecules interactions of monolayers, which was achieved through adsorptive analysis methods including adsorptive process, density profile, density distribution and surface potential energy. Analysis on surface potential energy demonstrated that the adsorptivity of amorphous smooth substrate is uniformly distributed over the surface, while DLC substrates with different surface morphologies appear to be more potentially corrugated, which improves the adsorptivity significantly. Because of the large distance of molecules from carbon atoms located at the square groove bottom, substrate-molecules interactions vanish significantly, and thus potassium stearate molecules cannot penetrate completely into the square groove. It can be observed that the equilibrium substrate-molecules interactions of triangle groove and semi-circle groove are much more powerful than that of square groove due to geometrically advantageous properties. These findings provided key information of optimally design of solid substrates with controllable adsorptivity. [ABSTRACT FROM AUTHOR]

Revealing the ductile deformation mechanisms of ultra-hard brittle cubic silicon carbide (3C-SiC), as well as their correlations with microstructure evolution, are crucial for facilitating the ductile machinability of the ceramic material. In the present work, we report the formation of highly oriented high density stacking faults accompanied with suppressed amorphization and cracking in polycrystalline 3C-SiC in ultrasonic elliptical vibration-assisted diamond cutting, which contributes to significantly enhanced ductile material removal of the ceramic material compared to ordinary cutting. Specifically, characterizations of Raman spectroscopy on machined surface and cross-sectional transmission electron microscopy on subsurface, as well as molecular dynamics simulations of the two kinds of cutting processes, are jointly performed to elucidate the mechanisms of phase transformation and microstructure evolution that govern the ductile material removal of polycrystalline 3C-SiC under the vibration assistance. In particular, the formation mechanisms of highly oriented high density stacking faults emitted from grain boundaries are revealed. Current findings provide insights into the ductile deformation behavior of hard brittle ceramics enhanced by field-assisted deformation process. [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]

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]

Abstract: In this paper we report molecular dynamics based atomistic simulations of deposition process of Al atoms onto Cu substrate and following nanoindentation process on that nanostructured material. Effects of incident energy on the morphology of deposited thin film and mechanical property of this nanostructured material are emphasized. The results reveal that the morphology of growing film is layer-by-layer-like at incident energy of 0.1–10eV. The epitaxy mode of film growth is observed at incident energy below 1eV, but film-mixing mode commences when incident energy increase to 10eV accompanying with increased disorder of film structure, which improves quality of deposited thin film. Following indentation studies indicate deposited thin films pose lower stiffness than single crystal Al due to considerable amount of defects existed in them, but Cu substrate is strengthened by the interface generated from lattice mismatch between deposited Al thin film and Cu substrate. [Copyright &y& Elsevier]

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]

TLK (Terrace-Ledge-Kink) structure such as surface steps is often found on the surface of SiC materials. Removal behavior of SiC substrates with TLK structure has not been studied in a fixed abrasive polishing under nano-abrasion conditions. In this paper, the effect of TLK structure on the abrasion temperature, stress, and structural transition of SiC substrates during the nano-abrading process is pursued by molecular dynamics (MD) simulation. The results show that the average stress and temperature decrease with the increase of ledge numbers in the TLK structure. It is found that crystalline-to-amorphous (C–A) phase transition occurs. The high-density amorphorization of SiC is induced by a high shear stress, which transforms to low-density amorphous SiC with the release of shear stress. Furthermore, unlike previous reports, the pressure-induced 6-fold coordinated structure in 3C–SiC in this study, however, does not possess a high-pressured phase transition (HPPT) to rocksalt structure; instead, a disordered structure is found. The ductile domain removal goes through two stages: first through the dislocation nucleation and propagation at the initial abrading stage and is then followed by the plastic flow of the amorphous atoms after sliding over the ledge. The presence of TLK structures benefits the plastic deformation of the SiC substrate. [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]

Molecular dynamics (MD) simulations were performed to investigate the adsorption of potassium stearate molecules on diamond-like carbon (DLC) substrate. The effects of non-bonded interactions and confinement conditions on the adsorption were investigated. The confinement conditions performed herein were achieved by imposing a Z-direction constraint on the movement of molecules in the initial stage of adsorption, and then releasing the molecules from the constraint gradually. Our simulation results show that the polar end groups of molecules tended to accumulate during the adsorption, and the final distribution of adsorptive film without confinement was irregular. Under confinement conditions, the adsorptive film was evenly distributed on the substrate after reaching its equilibrium configuration, and the final inter-subsystem potential of the substrate on adsorptive film was obviously decreased as compared with the results without confinement. These findings provided an effective approach for promoting the adsorption of molecules. [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 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 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]

In the present work, we propose a novel thermo-chemical post-processing method for refining the mechanically polished surface of natural diamond crystal. The deformation mechanisms of diamond crystal during mechanical polishing are elucidated by Raman Spectroscopy corroborated by molecular dynamics simulations. Moreover, the surface mechanical properties of diamond crystal are qualitatively characterized by nanoindentation tests. Our results reveal that under mechanical polishing there are phase transformations from diamond carbons to layered graphite, amorphous sp 3 and sp 2 hybrided structures occurred in the topmost surface layer, which consequently deteriorates the intrinsic surface strength of diamond crystal. In the following thermo-chemical refinement, the polishing-induced amorphous carbons, layered graphite and internal stress are largely removed through the weak oxidation reaction. It is found that the formation of considerable graphene structures in the topmost surface layer results in an ultra-hard diamond crystal surface with dramatically enhanced hardness and Young's modulus. Our findings shed light on the preparation of natural diamond crystal surface with superior mechanical properties. [ABSTRACT FROM AUTHOR]

Experiment and molecular dynamics simulation results of ultraviolet nanosecond laser micromachining of monocrystalline diamond demonstrate the formation of fruitful highly ordered graphite layer between top amorphous layer and bottom diamond, with visible boundaries among them. [Display omitted] • UV ns laser ablation mechanisms of monocrystalline diamond is explored. • Crack-free precise microgroove is fabricated on monocrystalline diamond. • Formation of highly oriented graphite layer in ablated diamond is discovered. • Laser fluence has a strong influence on diamond-to-graphite transformation. Inducing highly oriented graphite layer as buried conductive media in diamond by laser ablation is crucial for promoting the electronic functionalities of structured monocrystalline diamond. In the present work, we fabricate surface microgrooves with high precision and limited heat affected zone on monocrystalline diamond by low cost ultraviolet nanosecond pulsed laser micromachining. In particular, fruitful highly oriented graphite layer is formed between top transformed amorphous layer and bottom pristine diamond, with visible regular boundaries among them. Raman spectroscopy and high-resolution transmission electron microscopy characterization are jointly utilized to identify the phase transformation-induced microstructure evolution in subsurface of ablated diamond. Furthermore, molecular dynamics simulations are performed to elucidate the underlying ablation mechanisms, as well as predict the dynamic ablation process of nanosecond pulsed laser micromachining of diamond. Finally, the effect of laser fluence on the machined surface morphology and the phase transformation characteristics of the ablated diamond is addressed. [ABSTRACT FROM AUTHOR]

• Molar ratio design of PPSC mix ratio. • The composition of PPSC was optimized by simulation method. • The effect of chemical composition on the mechanical properties of PPSC was simulated. In this paper, the mechanical properties of excess-sulfate phosphogypsum slag cement (PPSC) were studied by experimental data, microscopic tests and molecular dynamics (MD) simulations. Specifically, the properties of PPSC in terms of setting time, compressive and flexural strengths were investigated by experiment. The hydration products of PPSC were tested and observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furtherly, at the atomic scale, the relationship between nanoscale and macroscopic mechanical properties of PPSC was established. The mechanism of the effect of chemical composition on the mechanical properties of PPSC was studied at multiple scales, and the compound synergistic effect between chemical compositions was further studied. The results show that the mechanical properties of PPSC increase with the increase of CaO/SO 3 , and decrease with the increase of SiO 2 /Al 2 O 3. CaO and Al 2 O 3 can improve the mechanical properties of PPSC. The high mobility and structural instability lead to CaO/SO 3 has greater effect on the mechanical properties of PPSC than that of SiO 2 /Al 2 O 3. When CaO/SO 3 is 1.8 ∼ 2.0 and SiO 2 /Al 2 O 3 is 3.5 ∼ 3.7, the mechanical properties of PPSC are better. Moreover, when CaO/SO 3 is 2.0 and SiO 2 /Al 2 O 3 is 3.5, the mechanical properties of PPSC are the best. At this time, the compound synergistic effect of alkaline activator and sulphate activation is the best. This paper provides an important reference for the composition design and application of PPSC. [ABSTRACT FROM AUTHOR]

Detwinning is a unique deformation mechanism of nanotwinned metals with twin lamellae thickness down to a few nanometers. In this work we investigate the impact of detwinning mechanism on the tensile ductility of twinned Cu nanowires containing high density of parallel twin boundaries by means of molecular dynamics simulations. Simulation results show that the fracture strain of twinned Cu nanowires has a strong dependence on twin boundary spacing, resulting from the competition between individual deformation modes. Particularly for the twinned Cu nanowires containing the thinnest twin lamellaes, the dominant detwinning mechanism leads to a significant reduction in the tensile ductility. It is found that detwinning originates from twin boundary migration, which is a result of the glide of lattice partial dislocations on the twin planes. This work advances our fundamental understanding of the twin boundary-related mechanical properties of twinned metallic nanowires. [ABSTRACT FROM AUTHOR]

Interfaces play key roles in determining mechanical properties of materials. In current work we perform molecular dynamics simulations of diffusion bonding to evaluate the effect of temperature on the morphology of the Ni/Al interface and the strength of the diffusion bonded Ni/Al nanowires. The centro-symmetry parameter is adopted to identify defect atoms generated. Simulation results show that the thickness of the Ni/Al interface has strong dependence on the temperature of diffusion bonding. Following uniaxial tension tests indicate that the yield strength of Ni/Al nanowires is smaller than both the single crystalline Ni and Al nanowires, because of the Ni/Al interface acting as dislocation source and the mobilization of pre-existing dislocations at high temperature. It is shown that the mechanical properties of diffusion bonded Ni/Al nanowires strongly depend on the temperature. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical and tribological properties of multilayers with nanometer thickness are strongly affected by interfaces formed due to mismatch of lattice parameters. In this study, molecular dynamics (MD) simulations of nanoindentation and following nanoscratching processes are performed to investigate the mechanical and tribological properties of Ni/Al multilayers with semi-coherent interface. The results show that the indentation hardness of Ni/Al multilayers is larger than pure Ni thin film, and the significant strength of Ni/Al multilayers is caused by the semi-coherent interface which acts as a barrier to glide of dislocations during nanoindentation process. The confinement of plastic deformation by the interface during nanoscratching on Ni/Al multilayers leads to smaller friction coefficient than pure Ni thin film. Dislocation evolution, interaction between gliding dislocations and interface, variations of indentation hardness and friction coefficient are studied. [Copyright &y& Elsevier]