Serendipitous Deposition of Composite Coatings by Aerosol Deposition

Aerosol deposition (AD) is an innovative solid-state spray method for producing dense ceramic films at room temperature. Effective pretreatment of feedstock powders is crucial for achieving dense coatings in AD. Ball milling modifies non-optimal powders by reducing particle size and inducing surface cracks, which broadens the deposition window and increases deposition rate in AD.

In this study, we aimed to deposit alumina (Al₂O₃) coatings from powder consisting of dense particles by AD. The powders were ball milled with zirconia (ZrO₂) milling media for 0 to 9 hours to improve the deposition rate. We investigated the impact of high-energy ball milling on the shape, size and crystal structure of the Al₂O₃ powders, as well as the deposition rate. The results show that ZrO₂ debris adheres to the Al₂O₃ powder surfaces; the amount increasing with milling time. Dense, thick coatings were deposited on silicon substrates via AD using the ball-milled powders. The coatings exhibited a composite structure with unique zebra patterns, consisting of approximately 40 % by volume of ZrO₂, minimal cracks, and high hardness.