Development of de-alloyed zones during oxidation: effects on microstructure and spallation behaviour

The development of de-alloyed zones during oxidation of; martensitic and au stenitic steels and Ni based superalloys has been reviewed and the influenc e of de-alloying on local creep strength has been assessed. The de-alloyed zones in martensitic steels have similar, possibly higher, strength than th e bulk material, whereas in Ni based superalloys the de-alloyed zone is sig nificantly weaker than the bulk alloy. The effect in austenitic steels vari es according to the strengthening phases present in the alloys: the de-allo yed zone is weaker in alloys strengthened by chromium carbides and/or gamma ' but has similar strength in alloys strengthened by niobium carbide.