QUANTITATIVE CHARACTERIZATION OF THE STRUCTURE OF PLASMA-SPRAYED AL2O3 COATING BY USING COPPER ELECTROPLATING

The structure of a plasma-sprayed Al2O3 coating was studied by observing copper deposited in the coating by electroplating. The distribution of copper in the microstructures of the electroplated coating revealed clearly the existence of micropores, a non-bonded area between ceramic lamellae, and microcracks in individual flattened particles in the coating. It becomes possible to determine clearly a lamella in a coating and to examine detailed structures of the coating from a cross-section of a single flattened ceramic particle. The mean thickness of flattened ceramic particles, vertical crack density in the individual particles and mean bonding rate to the coating are introduced to characterize the structure of a ceramic coating. It was recognized that a flattened ceramic particle can be regarded as a disc which has the same thickness. It becomes clear that the average bonding rate between ceramic lamellae is only about 30% for the coating commonly used. Furthermore, it was also recognized that many microcracks perpendicular to the lamellae are distributed uniformly in the coating and almost all the microcracks run across the lamellae.