[en] 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.

[en] Highlights: • An AFM-based depth prediction model of nano-grooves for the atomic force microscopy (AFM)-based multi-passes scratching method is given. • The effect of the tip geometry is considered in the theoretical model. • A correction factor is introduced into the two-passes scratching model and the prediction error of the correction model is less than 10%. - Abstract: This paper proposes a nano-groove depth prediction model for the atomic force microscopy (AFM)-based multi-passes scratching method in which the AFM tip is considered as a cone with a spherical apex. The relationship between the normal load applied on the sample and the depth of the machined nano-groove is systematically investigated for the multi-passes scratching process. Nano-grooves are fabricated with several normal loads and two passes scratches on a 2A12 aluminum alloy surface to verify the developed models. Results show that the hardness may become larger near the machined region after one pass scratching test and a correction factor is introduced into the two passes scratching model which is as a function of the first pass machined depths of the nano-grooves. Based on the correction model, several nano-grooves with an expected depth are machined with different normal loads for each pass in the two passes scratching tests and the difference between the experiment results and the expected values is less than 10%. Actually, to machine a nano-groove with a desired depth, this method has the potential to distribute the appropriate normal load applied for each pass to reduce the tip wear and be used for nano-groove depth correction using the multi passes scratching technique

[en] HIGHLIGHTS• Reflectivity of aluminum alloy is improved after being coated by gold film. • The optimal parameters combination of gold film are 45°C, 0.35 A, 140 s. • Adhesive force of gold film would be changed after holding at 60, −20°C. Aluminum alloys are widely applied in optical turrets after coating and super-finishing. Gold films prepared on aluminum alloy substrates via electron beam (e-beam) evaporation are considered to be effective way to realize close to total reflection of incident light. Here, we investigated the optimization of the reflectivity parameters of e-beam evaporated gold films; then, the influence of different deposition parameters on the surface quality, adhesive force and reflectivity (incident light in the 650–1700 nm range) of the film at −20, 25 and 60°C were systematically studied. The results demonstrated that the reflectivity and adhesion of the gold films both increased after high temperature holding and decreased slightly after low temperature holding. However, the surface morphology of the gold film did not change substantially. After holding at 60 and −20°C, the adhesive force decreased, which indicated that the adhesion strength between the reflective membrane and the substrate decreased.

[en] The properties of graphene can be chemically altered by changing its local binding configurations. In the present work, we investigate fundamentals of chemisorption of atomic hydrogen on graphene and its influence on mechanical properties of as-hydrogenated graphene by means of molecular dynamics simulations. Our simulation results indicate that there are diversiform hydrogen-graphene configurations formed in the chemisorption process. Especially, energetically favorable hydrogen pairs result in less even no atomic distortion of graphene than sp³ hybridization. The hydrogenation-induced deterioration of mechanical properties of graphene shows a strong dependence on its chirality. The evolution of bond structures in uniaxial tension along armchair direction is more sensitive to local failure of graphene than zigzag direction, leading to a more pronounced decrease in both fracture stress and fracture strain. It is indicated that the chemisorption of hydrogen on graphene can be strongly affected by operating temperature primarily due to the temperature dependent graphene morphology. These findings advance our understanding of chemical vapor deposition of graphene synthesis and hydrogenation of graphene. (paper)

[en] Highlights: • 3D Model was used to predict the laser ablation of AA 6061 before and after SiO₂ film. • Laser was utilized to redistribute to smooth the material pits and improve its performance. • The protective way of SiO₂ film reflected in the ablation depths and irradiation times. -- Abstract: In this work, the process of laser ablation of aluminum alloy 6061 (AA 6061) before and after silicon dioxide (SiO₂) coating was studied both experimentally and by numerical simulation. Four different laser fluences (0.5 J/cm², 1 J/cm², 1.5 J/cm² and 2 J/cm²) were applied to investigate laser ablation of AA 6061 before and after coated by SiO₂ film. It was founded that the thermal diffusion and ablation depth of AA 6061 had been directly influenced by both laser fluence and SiO₂ coating. At relatively low laser fluence (0.5 J/cm²), ablation deformation and damage of AA 6061 were not observed. While the laser fluence reached to 1 J/cm², vaporization took place in AA 6061. With increased laser fluence, the ablation range and depth expanded. The vaporization of SiO₂ films happened in the first laser fluence, however, the area of the zone affected were much less than AA 6061, that demonstrates the SiO₂ film has a positive effect on AA 6061. A 3-dimensional computational model was used to compute the temperature variation in a solid material over time. The results of the model (depth to width ratio versus laser ablation) exhibited well with the experimental results in some ways.

[en] 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 0.1-10 eV. The epitaxy mode of film growth is observed at incident energy below 1 eV, but film-mixing mode commences when incident energy increase to 10 eV 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.

[en] 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.

[en] This paper presents a novel atomic force microscopy (AFM)-based methodology for measurement of axial and radial error motions of a high precision spindle. Based on a modified commercial AFM system, the AFM tip is employed as a cutting tool by which nano-grooves are scratched on a flat surface with the rotation of the spindle. By extracting the radial motion data of the spindle from the scratched nano-grooves, the radial error motion of the spindle can be calculated after subtracting the tilting errors from the original measurement data. Through recording the variation of the PZT displacement in the Z direction in AFM tapping mode during the spindle rotation, the axial error motion of the spindle can be obtained. Moreover the effects of the nano-scratching parameters on the scratched grooves, the tilting error removal method for both conditions and the method of data extraction from the scratched groove depth are studied in detail. The axial error motion of 124 nm and the radial error motion of 279 nm of a commercial high precision air bearing spindle are achieved by this novel method, which are comparable with the values provided by the manufacturer, verifying this method. This approach does not need an expensive standard part as in most conventional measurement approaches. Moreover, the axial and radial error motions of the spindle can both be obtained, indicating that this is a potential means of measuring the error motions of the high precision moving parts of ultra-precision machine tools in the future. (paper)

[en] An atomic force microscopy (AFM)-based method to reveal the elastic recovery behavior of a polymer material after the nanoscratching process is presented. The machined depth during scratching is obtained by monitoring the position of the piezoceramic tube (PZT) of the AFM system. By comparison with the measured depth of the nanogroove, the elastic recovery of the machined depth can be achieved. Experiments are also undertaken to study the effects of the scratching velocity and the applied normal load on the elastic recovery of the machined depth when scratching on polycarbonate (PC). Results show that the elastic recovery rate has a logarithmically proportional relationship to the scratching velocity, while it has little change with the variation of the applied normal load. In addition, the constitutive model of the polymer material is also used to verify the obtained conclusions, indicating that this is a potential method for measuring the elastic recovery of the material under the mechanical process on the nanoscale. (paper)

[en] In the present work, we perform finite element simulations to investigate the ablated surface morphology of silicon by nanosecond pulsed laser ablation using low laser fluences ranging from 14.92 to 23.21 J cm⁻². The utilized finite element model comprehensively considers the following aspects: (1) combined effects of thermal conduction, convection and radiation on heat conduction; (2) temperature-dependent material properties; (3) instantaneous update of the laser focus due to evaporation-induced surface recession for low laser fluences; and (4) spatial and temporal Gaussian energy distribution of the laser pulse. Experimental work using the same laser machining parameters compared to the conducted finite element simulations are carried out to validate the simulation results. Through the optimization of the laser machining parameters by 2D and 3D finite element simulations and the respective experimental validations for eliminating heat-affected zone and promoting forming accuracy, high accuracy aligned micro-grooves are fabricated on silicon with high anti-reflective properties in a wide range of wavelengths between 400 and 2000 nm. This is fairly comparable with the performance of similar silicon microstructures by femtosecond laser ablation. Consequently, the current work presents a way to fabricate precise surface microstructures with high anti-reflective properties on silicon at low cost by nanosecond pulsed laser ablation. (paper)