Surface microstructure changes in the mechanically strained Fe–Al based intermetallics

Surface microstructural changes in Fe–28Al and Fe–28Al–5Cr–0.5Nb–0.2C (in at%) alloys during compressive creep tests at 873 and 923 K are investigated by optical and scanning electron microscopy. The differences in microstructure between the pure and alloyed Fe–Al intermetallic alloys are discussed using additional data on vacancy and dislocation formation derived from positron annihilation lifetime measurements and the hyperfine magnetic characteristics obtained from Mössbauer phase analysis. It has been found that an addition of Cr and Nb increases the thickness of the oxide Al2O3 surface layer formed at higher temperatures, influences grain size, defect structure, and rupture life of the specimen. Formation of an Al2O3 oxide layer leads to a reduction of Al content in Fe–Al and to a surface magnetic softening.