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Molecular Dynamics based Investigation of Aerosol Deposition versus Thermal Spray Deposition
GUANYU SONG, Huan Yang, Christopher J. Hogan, University of Minnesota
Abstract Number: 13
Working Group: Nanoparticles and Materials Synthesis
Abstract
Aerosol deposition (AD) is a coating technique leading to thick ceramic coatings by accelerating particles to supersonic speeds and impacting them with a substrate at reduced pressure and room temperature. AD can be contrasted with thermal spray deposition, wherein particles velocities are lower but thermal energies (temperatures) are higher. To better understand the differences between AD and thermal spray generated coatings, we perform large-scale (>105 atoms) molecular dynamics simulations of both the AD and thermal spray processes, as well as conditions intermediate to the two processes. Specifically, using yttria-stabilized zirconia (YSZ) nanoparticles (3-6 nm) as model materials on YSZ substrates, we examine the effects of deposition on the nanoparticle internal energy distribution, residual stress, and strain during deposition. These parameters are also examined for the substrate. Uniquely, AD and thermal spray deposition are simulated at equal translational plus thermal energies (i.e. the sum of half the impact velocity squared and 1.5 Boltzmann’s constant x temperature are equal in all simulations). The local internal energy distributions for nanoparticles during impaction show that in AD the bottom region of the nanoparticle is heated much more than the upper region when the nanoparticle reaches its maximum penetration into the substrate. Conversely, in thermal spray, particle internal energy distributions are much more uniform, as the degree of translational-to-thermal energy conversion is lessened. AD results in higher degrees of plastic deformation and residual stress than thermal spray at comparable total energy. Substrate temperatures increase to higher values in thermal spray deposition as compared to AD. Simulation results suggest that both processes can lead to strongly adhered, consolidated coatings from particle deposition, but that coating microstructure is affected by translational-to-thermal energy conversion during deposition processes.