Failure in which pieces of coating detach, leaving patches of bare bond coat or substrate. In thermal barriers it is the end-of-life mode, driven by TGO growth, ceramic sintering and thermal cycling stresses. In wear coatings it follows contact fatigue, impact or excessive coating thickness. Spall location and the layer exposed are the first clues in a failure investigation.
TBC spalling on the leading edge down to bond coat, those blades come out at the next outage.
Also heard as
- spallation
- spall
- chipping
Related terms
Thermal barrier coating
A ceramic coating system that insulates hot-section metal parts from combustion gas temperatures.
TGO
Thermally grown oxide: the alumina layer that grows between bond coat and ceramic in hot service.
Delamination
Separation of a coating from its substrate or of one coating layer from another.
Residual stress
Stress locked into a coating and substrate after spraying, from splat shrinkage, cooling and impact.
Same word, different worlds
Flaking of large chunks from a bearing race or gear tooth after fatigue cracks below the surface link up.
Refractories & Furnace LiningsCracking off of pieces or layers from the hot face of a refractory lining.
Gear EngineeringLarge, irregular flakes broken out of a tooth surface, usually where pits have grown and joined.
Concrete & CementChunks or flakes breaking away from a concrete surface or edge, often from corroding rebar beneath.
Sealants & WaterproofingConcrete, brick or stone breaking off in flakes or chunks at the surface.