Surface oxide cracking associated with oxidation-induced grain boundary sliding in the underlying alloy

When thin sections of FeCrAlY alloys having initially flat surfaces are oxidized at high temperature, the surface becomes uneven as some metal grains on the surface displace above and below the macroscopic surface. On subsequent cooling, the oxide formed by high-temperature oxidation cracks and spalls at the edges of the uplifted grains. Microstructural observations indicate that the grain uplift is associated with grain sliding and it proposed that the sliding at the oxidation temperature occurs in response to the evolving compressive growth stress in the oxide. The observed spalling patterns are consistent with a fracture mechanics model in which incipient flaws at the oxide-alloy interface, in the vicinity of the step edges, propagate in the residual stress field in the oxide.