Developing the ability to inform and tailor aerosol deposition coatings using laser induced particle impact testing

Aerosol deposition (AD) is a room temperature kinetic spray process that has been used to produce metallic, ceramic, polymeric, and blended coatings on a variety of substrates. This technique produces films through the impact consolidation of particles accelerated through a converging-diverging nozzle into a vacuum chamber. As a room temperature technique, the phase and stoichiometry of the feedstock material can be maintained after deposition. Additionally, temperature sensitive substrates, such as polymers can be coated with high melt temperature materials such as ceramics.

While AD is a versatile and effective technology, the process development can be time intensive. Generally, a design of experiment is needed to optimize the powder processing and spray parameters to successfully deposit and tailor the coatings. So, we are exploring the possibility of informing and tailoring AD coatings using laser induced particle impact testing (LIPIT) to push the boundaries of AD to new materials systems and expedite the process development for optimized coatings. LIPIT is a fast, inexpensive single particle impact test where particles or agglomerates of known size are fired at a substrate and the particle velocity is precisely measured. LIPIT enables high-throughput measurement of particles of various diameters over a range of velocities. The particles are observed to bounce, stick, or shatter and are characterized post-mortem using microscopy.

We have used the LIPIT to systematically explore the deposition of Al₂O₃ on Ni and Al₂O₃ on Al₂O₃. We have established qualitative agreement between AD and LIPIT, for both deposition (ball milled powder) and lack of deposition (as-received powder) of Al₂O₃. The LIPIT results indicate that whether the agglomerate bounces, sticks, or shatters is related to the agglomerate velocity but independent of the agglomerate diameter (and therefore momentum). Continued work is needed to establish the limitations of using LIPIT to inform AD for other material systems.