Deposition mechanism of alumina particles in aerosol deposition based on the kinetic energy of particles

In this study, the aerosol deposition process was used to deposit the α-Al2O3 coating on Mo substrate under various conditions, i.e., particle size, type of carrier gas, gas flow rate and a nozzle–substrate distance. The formation behaviors of the α-Al2O3 coating in terms of deposition rate, microstructure and texture were studied in a correlation with the kinetic energy of the particles forming the coating. The fully dense and crystalline α-Al2O3 coatings were observed with the average grain size of 20 nm, significantly smaller than the particle sizes of 0.14 and 1.0 μm. The coating layers under all conditions were examined with a fiber texture with the (0001) plane tilted about 15° away from the coating plane. The microstructure and texture formation were resulted by fragmentation and plastic deformation of the particles during the deposition. The deposition formation of the particle collisions with the coating was simulated by the finite element analysis with the fragmentation model. The model suggested that the particles fracture at the boundary of the maximum shear strain generated by the particle impact. The deposit is formed by the lower part of the fracture particle. The strain energy in the deposited area of retained particles is considered to be equivalent to the kinetic energy, which includes the effects of the particle characteristics and physical properties. The result indicated that the changes of the deposition rate and texture formation can be well explained as a function of the strain energy. Regardless of the strain energy, the density of the α-Al2O3 coatings was almost the same as that of the bulk α-Al2O3 material. It was found that the high strain energy can lead to both high deposition rate and high indentation hardness.