Growth Process of α‐Al 2 O 3 Ceramic Films on Metal Substrates Fabricated at Room Temperature by Aerosol Deposition

The aerosol deposition method (ADM) is a novel coating process that works at room temperature without a high‐temperature plasma and arc discharge, unlike the existing thermal spray coating. The bonding of the sprayed ceramic particles in this process is based on shock loading solidification, resulting from the impact of ceramic particles—it forms a dense, uniform, and hard ceramic layer at room temperature. However, its deposition mechanism has not been fully clarified. To clarify the growth mechanism during ADM, the initial growth stages of Al 2 O 3 films were investigated through observation of their microstructures. A series of observations confirmed that the bonding mechanism of substrate particles is related to plastic deformation, combined with an anchoring layer formed between the Al 2 O 3 layer and the Cu substrate. In addition, particle‐to‐particle bonding was caused by the plastic deformation as well as fractures of the starting ceramic particles. This cracking of particles was supposed by a broadening of the X‐ray diffraction pattern and decrease in crystallite size with an increasing number of scans. The results of atomic force microscopic images and surface profiles showed that these phenomena, such as the plastic deformation and the cracking of particles, result from the hammering effect of a bombardment by the subsequent particles.