Interfacial phenomena in the plasma spraying Al2O3+13 wt.% TiO2 ceramic coating

The interface between the bond layer and ceramic layer as well as between t he bond layer and the substrate in a duplex coating system consisting of a NiCrAl bond coat layer and an Al2O3 + 13 wt.% TiO2 ceramic coat layer has b een investigated by scanning electron microscopy and transmission electron microscopy. The lamellar bond layer mainly consists of lamellae aligning ap proximately parallel to the substrate surface, in which the individual lame llae consist of a thin outer amorphous and nanocrystalline film, an interme diate layer of fine columnar and equiaxed grains and an inner microcrystall ine region of big columnar grains. The morphology of the interfacial region s of the above two interfaces is shown to be similar and consists of a thic kness of 0.7 mum, or far less, of a mixture of amorphous and nanocrystallin e phases. However, besides a certain percentage of area of perfect contact, a small amount of area of non-contact has also been detected among the lam ellae or at the interfaces. (C) 2001 Elsevier Science B.V. All rights reser ved.