Scratch induced failure of plasma sprayed alumina based coatings

A set of plasma sprayed coatings were obtained from three alumina based top coat and two bond coat powders. Scratch test was undertaken on these coatings, under constant and linearly varying load. Test results include the lateral force data and scanning electron microscope (SEM) images. Failure occurred by large area spallation of the top coat and in most cases tensile cracks appeared on the exposed bond coat. The lateral force showed an increasing trend with an increase in normal load up to a certain point and beyond this, it assumed a steady average value. The locations of coating spallation and occurrence of maximum lateral force did not coincide. A bond coat did not show a significant role in determining the scratch adhesion strength.

► Scratch induced failure of alumina based coatings including nanostructured is reported.
► Ceramic is deposited on bond coat instead of steel, emulating a realistic situation.
► Lateral force data is supplemented with microscopy to observe coating failure.
► The failure mechanism during scratching has been identified.
► Critical load of failure has been calculated for each bond-top coat combination.