Microstructural features of mechanical failure in thermal barrier coating systems under static loadings

Abstract

In order to clarify qualitatively and quantitatively the failure mechanism of plasma-sprayed thermal barrier coating (TBC) systems from the microstructural viewpoint, in situ observation of the mechanical failure behavior was conducted for TBC systems under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. Several kinds of TBC systems were prepared by using different sorts of ceramic coating materials. Mechanical tensile loading or compressive loading was gradually applied to the plate shape of TBC specimen using a four-point bending test methodology. It was found that the tensile failure behavior of TBC systems depends strongly on the top-coat microstructures as well as heat treatment after the plasma spraying. The compressive failures were also found rather incidental and depended on the strength of top-coat at the interfacial region. Among different TBC systems, those with the finely segmented top-coat exhibited a good spalling resistance.