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The break-up of microparticle surface oxides is needed to generate a clean metal-metal contact for metallurgical bonding during impact events such as seen in cold-spray. However, the mechanism by which this occurs is not clear. Using a laser-induced particle impact tester, we conduct site-specific experiment of single Cu microparticle impacts on a polished Cu substrate and characterize the impact sites. We observe that oxide layers on the particles begin to delaminate at velocities high enough to cause jetting of the substrate around the periphery of the impact site. We show that the energy cost of such delamination is ∼30% of the energy needed to slow and stop particle as it bonds to the substrate, with the remainder being associated with the jetting process and bonding itself. At higher velocities, the oxide barrier is broken up to permit metallurgical bonding. Closer to the particle south-pole where hoop strain is low, oxide layers break up with few gaps and thus no metallurgical bonding is observed. Away from the south-pole where larger strains develop, oxide breakup permits intermittent bonding by the extrusion of bare metal into the gaps between oxide islands. These observations provide new insights towards understanding impact-induced metallurgical bonding during cold-spray process.

Although ceria particles are currently receiving great interest with their unique catalytic and optical properties, the problem of agglomeration is yet to be overcome, which is caused by their high density and surface energy, consequently hampering the practical applications. Herein, a novel method of preparing hierarchical shells of ceria (CeO2) and silica (SiO2) on a polystyrene (PS) core is introduced to control the shape and surface charge of the particle, which give rise to different dispersion conditions. The PS/CeO2/SiO2 hybrid core–shell microspheres provide a wide spectrum of surface charge via adjustment of the thickness of the outermost silica shell from 20 to 40 nm, which sets the isoelectric point (IEP) in the range of 5.1–8.6. Subsequently, the silica shell significantly extends the product’s stability and utilization windows due to the controlled surface charge and affinity between the particle surface and the dispersion medium. The developed multilayered core–shell microspheres and the method of synthesis have great potential for various applications that require sophisticated control of surface properties.

Molecular dynamics (MD) simulations are performed to study the near-surface deformation during nanoscratching on nanocrystalline Al. The influence of Si particle on wear behavior of nanocrystalline Al is also investigated by MD simulation. It is shown that the local deformation in nanocrystalline Al workpiece is associated with one or more mechanisms: (1) grain boundary (GB) migration, (2) GB sliding, (3) grain rotation, and (4) dislocations and deformation twin emitting from the indenter-workpiece interface and GBs. Moreover, the coarsening of Al grains is observed as the scratch proceeds. During grain coarsening, the low angle GB dissociates while the high angle GB migrates without dissociation. Interestingly, the GB motion is more active in nanocrystalline Al workpiece than that in Al/Si workpiece. The presence of Si particle changes the stress state of the adjacent Al grains, and therefore enhances the stability of GBs. Meanwhile, the specific wear rate in Al/Si workpiece is significant less than that in nanocrystalline Al workpiece, indicating that the Si particle enhances the wear resistance. In summary, this study sheds light on the interaction mechanism of second-phase and nanocrystalline matrix under sliding wear, which can provide theoretical support for the design of metal matrix composite with excellent wear resistance.

In this study, we proposed a multiscale analysis method that integrates the direct simulation Monte Carlo (DSMC) method and all-atom molecular dynamics (MD) simulation to comprehend the process of unsteady plasma spray coating of yttria nanoparticles (YNPs) on an alumina substrate. The correlation between the increase in the powder feed rate and growth mechanism of the film microstructure was obtained by solving the collisions of the sprayed YNPs and corresponding spatial trajectories. The results showed that higher powder feed rates form a wider spray cone angle, and a reduction in spray distance increased the probability of powder impinging normal to the substrate. This also explained the changes in the interfacial adhesion and hardness of the films with the powder feed rate and spray distance observed in the experiments. In particular, vertically incident YNPs not only constituted the densest bulk layer, but also contributed to strong adhesion by increasing the probability of generating Y-O-Al binding structures at the interface. The findings were the first to examine the complexity of chemo-mechanical behavior between spatial particle trajectories and facing material, thus throwing light on an important factor in the quality of sprayed ceramic coatings.

In view of the excellent water lubrication performance of Si3N4, the composite coatings of Ni/Si3N4 with different Si3N4 particle contents were fabricated and the ultra-low friction coefficient of the coatings sliding against Si3N4 ball in water was expected. Experimental results manifested that only the Ni/Si3N4 composite coatings with a high particle content can achieve the ultra-low friction coefficient (0.008). The SEM and 3D profiler measurements indicated that the formation of consecutive and smooth contact interface is one of the essential conditions to achieve the ultra-low friction. Besides, the tribo-chemical product, silicon hydroxide, is another requirement. The major wear mechanism changes from the mechanically dominated wear during the running-in process to the tribo-chemical wear at the ultra-low frictional stage. Such result indicates that low friction is not a specific feature of Si3N4 and SiC self-mated pairs. This behavior of ceramic composite coating may develop a new approach for the low energy loss water lubrication systems.

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 μm/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 μs exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 μm, with approximately 1 μm periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800–00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.

Superhydrophobic coatings with a rough structure and low surface energy have been regarded as new high-efficiency anti-dust solutions. However, current research on the anti-dust mechanism of superhydrophobic materials is still insufficient. Main obstacles are the difficulty in determining the contact state between the dust particle and the rough structure and calculating the contact force accurately. Herein, a new methodology that introduces rough surface discretization and extends the Johnson-Kendall-Roberts (JKR) model to solve the adhesive contact forces of a particle-rough surface was proposed. Further, the lattice Boltzmann method coupled with the JKR-based discrete element method was employed to study the particle deposition characteristics on superhydrophobic surfaces with randomly distributed rough structures. Surfaces with different rough structures were reconstructed using the fast Fourier transformation method. The particle-airflow and rough surface-airflow interactions were calculated using the immersed moving boundary method. The coupling models and computation scheme were validated by comparing the simulation results with those recorded by a high-speed camera. The effects of the particle diameter, airflow inlet velocity, surface energy, and surface structures (characterized by skewness, kurtosis and standard deviation) on particle migration, deposition morphology and deposition rate were compared and analyzed. The results indicate that smaller particles with larger velocities are less likely to be deposited on superhydrophobic surface. Increasing the surface energy of the rough surface can significantly enhance the particle deposition rate owing to the strong particle–surface adhesion force. Further, appropriate surface roughness can reduce particle–surface adhesion and particle energy dissipation during collision, thereby leading to a deposition reduction. However, excessive peaks and deep valleys on the rough surface would hinder the rolling and translation of the particles, thereby resulting in particle accumulation on the surface. Finally, using superhydrophobic surfaces with a skewness of 0 and kurtosis of approximately 5.0, and appropriately reducing the standard deviation of the rough-surface structures can significantly enhance the effect of superhydrophobic surfaces on anti-dust performance.

The sintering of nanostructured catalysts poses a grand challenge in understanding the complex mechanism in the experimental phenomena, as well as the structure-activity relationship. Here, we systematically investigate the structure-activity relationship of sintered Fe-based catalysts, including Fe2C, Fe5C2, Fe3C and pure Fe, in the CO activation by reactive molecular dynamics simulations. The results show that the sintering structures can promote the turn-over frequency of Fe3C compared with its un-sintered near-size structures, which might be attributed to the formation of low-coordination-number atoms. The change of surface area shows a similar trend for FexCy and pure Fe, and its increased magnitude varies with the content of carbon in the FexCy bulk. For size effect, the Fe2C displays the largest turn-over frequency for the 4.34 nm particle. The CO2 formation mechanism has also been compared for different FexCy, which may provide critical theoretical insights for industrial reduction of CO2 emission.

The high entropy alloy (HEA) is a potential material for coating because of its high hardness and wear resistance. In order to study the wear performance and protection ability of FeNiCrCoCu HEA coating on Cu substrate, the friction behavior of abrasive particle and material wear and damage were studied by molecular dynamics (MD). The cutting of depth and velocity of abrasive particle were used as variables for simulation. By analyzing the mechanical data of results, it was found that the friction coefficient of abrasive particle decreased gradually with the increase of the cutting of velocity. Dislocation extraction analysis (DXA) and Common neighbor analysis (CNA) were used to analyze the lattice structure and dislocations. By analyzing the above data, the wear and damage of the material was obtained, and the inhibition behavior of Hirth dislocation lock on dislocation nucleation was found. Cu substrate damage results showed that HEA coatings could effectively improve the wear resistance of the material surface. In the case of small cutting of depth, the high stress region in the material was concentrated below the abrasive particle, and the material subsurface damage would be intensified. This research can provide a theoretical basis for the application of HEA coatings.

Using chemically modified supports is a strategy to differentiate metal deposition, catalyst morphology and properties and, ultimately, the electrochemical activity towards the multiparametric and structure-sensitive Oxygen Reduction Reaction (ORR). Functionalized carbon nanotubes with pyridine groups, oxpyMWCNT, is a support that allows fine spatial dispersion of nanoparticles. This work reports the development of Pt supported on oxpyMWCNT with different metal loadings using the polyol method in alkaline reaction media. The effect of the pH value of the reaction solution and the reduction time on the deposition, the morphological and surface characteristics of the formed electrocatalysts was thoroughly investigated. The electrochemical performance of the aforementioned electrocatalysts towards ORR was evaluated. By using the aforementioned support, small particle size and fine and homogeneous dispersion were achieved that allowed the correlation between the properties and the electrocatalytic activity. Thus, there is a discussion about how mass and specific activity towards ORR are simultaneously affected by metal-support interactions, interparticle distance (particle proximity) and nanoparticle size.