Abstract
Alumina (Al2O3)-coatings were fabricated by a metal–organic chemical vapor deposition at a substrate temperature of 950°C using two different precursor evaporation systems. The application of a screw feeding system for precursor delivery leads to the formation of coatings with a nanolamellar microstructure while precursor evaporation directly from a crucible produces coatings without a specific microstructure. X-ray diffraction measurements show that both kinds of coatings consist of transitional Al2O3. Closer investigations of the lamellar structured coating by means of transmission electron microscopy reveal that the lamellae result from periodical fluctuations of nanoporosity and grain size. Annealing experiments show that the laminated microstructure is stable at high temperatures. Even though the coatings transform completely into α-Al2O3 after heat treatment at 1200°C and nanopores coalesce to larger pores, a through-thickness lamellar coating morphology is maintained.
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