Effect of substrate hardness and surface roughness on the film formation of aerosol-deposited ceramic films

Abstract

The aerosol deposition (AD) method is a novel ceramic coating technique that allows manufacturing of dense ceramic films at room temperature directly from ceramic powders without any high temperature sintering steps and without expensive (ultra) high vacuum processes. The deposition mechanism can be separated into two stages: the creation of an anchor layering and the subsequent film formation. Step one involves an initial plastic deformation of the substrate surface by the first impacting particles. Especially in the first stage, substrate properties affect the deposition and determine the dominant bonding mechanism. Ductile substrates can be expected to give strong film anchoring, whereas high hardness substrates might require higher particle velocities to form adhering layers. In this study, the influence of the substrate hardness in combination with the surface roughness on the deposition was investigated. Four ceramic substrates (two types of Al2O3, sapphire, and LTCC) with different hardness and surface roughness were coated with Al2O3 in order to study the formation of an anchoring layer and their effect on the deposition rate. As a result, no anchoring layer was found on the hard ceramic substrates.