With the high interest in aerosol deposition in order to form high-quality coatings by solid-state impact, there is an increasing demand for developing general guidelines to estimate needed particle velocities and thus process parameter sets for successful deposition of ceramic materials. By using modeling approaches, rather different material properties in first instance can be expressed in terms of binding energies. Needed velocities for possible bonding can then derived by impact simulations and compared to experimental results from the literature. In order to study the role of binding energy on the impact behavior of ceramic particles in aerosol deposition, a molecular dynamics study is presented. Single-particle impacts are simulated for a range of binding energies, particle sizes and impact velocities. The results show that increasing the binding energy from 0.22 to 0.96 eV results in up to three times higher characteristic velocities corresponding to the threshold of bonding or grain size-dependent fragmentation of the particles. However, regardless of the binding energy, exceeding the characteristic velocities results in a similar deformation and fragmentation pattern. This allows for a general representation of the impact behavior as a function of normalized impact velocity for different ceramic materials. Apart from dealing with prerequisites for bonding of different materials by aerosol deposition, this study could also be generally relevant to the high-velocity deformation behavior of ceramics with different grain sizes.

Aerosol deposition (AD) enables the formation of dense ceramic coatings by high velocity impact of submicron‐sized particles. However, up to now, it is still not clear how the material properties of the ceramic powder particles influence their impact behavior and possible success in layer build‐up in AD. Therefore, in order to provide a broader understanding, this study utilizes molecular dynamic (MD) simulations to investigate the impacts of single‐crystalline particles while manipulating binding energies, particle sizes, and impact velocities, addressing a rather wide range of different materials and process conditions. The findings reveal that increasing binding energies from 0.22 to 0.96 eV necessitates up to three times higher velocities to reach thresholds for bonding and fragmentation, which are linked to potential layer formation. For conditions above the velocity thresholds given by individual binding energies, similarities in the deformation and fragmentation patterns are derived. Consequently, rough estimations regarding the required particle impact velocities for AD of different materials can be inferred.

A good understanding of influencing parameters is required to predict corrosivity in marine and coastal environments. This study investigated the influences of real-time data of (i) air temperature, (ii) sensor surface temperature, (iii) relative humidity, (iv) precipitation, and (v) wind on steel corrosion via data analysis. The results revealed that the time when the sensor surface temperature is below the dewpoint temperature reveals the best correlation with corrosion. Wind speed above 5 m s −1 also correlated with corrosion. At the test site, most of the corrosion occurred during autumn and winter, due to more water condensation and more wind. During spring and summer, there was little corrosion, due to little condensation and dry surfaces.

Accelerated testing is widely used in development and pre-qualification of protective organic coatings. In this work 26 coating systems have been investigated in a 2-year C5 atmospheric exposure field test, ISO 9227 salt spray test, ISO 12944-9 cyclic ageing and ISO 16773 electrochemical impedance spectroscopy measurement of coating resistance. Of the 26 coating systems, 16 have epoxy mastic primers and 10 have zinc rich epoxy primers. In the field test, the zinc rich primer improved corrosion creep resistance from scribe by a factor of about 10. However, this is not reflected in any of the accelerated lab tests. The lab tests all show rather poor correlation to the field test with respect to corrosion creep. All the coatings had little corrosion creep from scribe in the field test, even the coating systems with epoxy mastic primers. The large focus on this parameter in coating pre-qualification testing, e.g. in ISO 12944-6 and 12944-9, may therefore not be justified.

The deformation and bonding of particles in Aerosol Deposition (AD) is a topic of growing technological interest for solid-state coating and additive manufacturing with ceramic materials. The core feature of the AD process is the unexpected plasticity of ceramics at high strain rates and small length scales, which is also a topic of general interest for understanding the response of intrinsically brittle materials to dynamic deformation. We explore this feature through computational analysis of the impact of ceramic particles - modelled based on a Lennard-Jones description of submicron TiO2-anatase particles in a two-dimensional molecular-dynamics system - onto a substrate at a range of impact velocities (100-800 m/s). The deformation behaviour of the particle for each impact velocity was analysed with respect to the evolution of the stress, strain, and temperature fields. The results reveal indications of dislocation-based plasticity within a certain velocity regime. This velocity regime, which becomes narrower with increasing the particle size, coincides incidentally with bonding of particles to the substrate in AD. The results also show that outside this regime, the impact is associated predominantly with either rebounding (at lower velocities) or particle fracture (at higher velocities). The simulation results are interpreted in view of a phenomenological model of fragmentation, considering the interplay between the ma-terial properties, such as the fracture energy, and the kinetic energy of particles upon impact. Based on the simulations and the analytical model, a window of deposition is proposed for AD.

Up to now, the role of particle sizes on deformation features of ceramic particles in aerosol deposition (AD), is not fully understood. For distinguishing general features, two-dimensional molecular dynamics (MD) simulations are applied to study associated phenomena. The nanoparticles are assumed to have original sizes of 10-300 nm and to impact the substrate at velocities of 100-800 m/s. The applied Lennard-Jones potential for the modelled nanoparticles were adjusted to mimic the mechanical properties of TiO2-anatase. For small particles, the simulations reveal three different impact behaviors of (i) rebounding, (ii) bonding and (iii) fragmentation based on initial size and impact velocity, whereas, the larger ones do not show the bonding behavior. The upper limit of the bonding regime shrinks with increasing particle sizes, the field then diminishing for the largest ones. The different impact phenomena were analyzed by evolution of the stress, strain and temperature fields. Stress and strain field results showed that “localized inelastic deformation” occurred at particle sites spreading from the interface to the substrate to the particle core. Calculated temperature fields show a local rise of around 1200 Kelvin due to the inelastic deformation, which is probably sufficient for thermal activation of further deformation features.

Up to now, the role of particle sizes on the impact behavior of ceramic particles in aerosol deposition not yet fully understood. Hence, with the aim to supply a more general understanding, modeling series of low strain rate compression and high-speed impact were performed by molecular dynamics on single-crystalline particles in sizes of 10-300 nm that are tuned to match mechanical properties of TiO 2 -anatase. The modeling results reveal that particles with original diameter of 25-75 nm exhibit three different impact behaviors that could be distinguished as (i) rebounding, (ii) bonding and (iii) fragmentation, depending on their initial impact velocity. In contrast, particles larger than 75 nm do not exhibit the bonding behavior. Detailed stress and strain field distributions reveal that combination of “localized inelastic deformation” along the slip systems and “shear localization” cause bonding of the small and large particles to the substrate. The analyses of associated temperature rise by the inelastic deformation revealed that heat diffusion at these small scales depend on size. Whereas small particles could reach a rather homogeneous temperature distribution, the evolved heat in the larger ones keeps rather localized to areas of highest deformation and may support deformation and the formation of dense layers in aerosol deposition.

Impact behavior of intrinsically brittle materials at the nanoscale is a topic of growing interest, for instance, in aerosol deposition and cold spraying of ceramic materials. In this work, we examine the behavior of single-crystalline brittle nanoparticles upon impact on a rigid substrate, within the framework of a molecular dynamics model. The model is based on Lennard-Jones formulation, where brittleness is brought about by using a relatively small cut-off interaction distance. Simulations have been carried out for different values of particle size and velocity. The results show that despite the induced brittleness, particles start to deform without breaking into fragments, as the particle size falls below a critical value. They also indicate that the deformation of particles can be accompanied by poly-crystallization and bonding to the substrate. The necessary conditions for deformation and bonding are also predicted in view of an analytical model of impact and fracture, considering the effects of particle size and surface energy. The results are summarized into a parameter selection map, providing an overview of the conditions for successful deposition of intrinsically brittle materials, in terms of particle size and velocity. The predictions are interpreted with respect to the results of the relevant kinetic spraying studies.