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 investigate d by optical and scanning electron microscopy. The differences in microstru cture between the pure and alloyed Fe-Al intermetallic alloys are discussed using additional data on vacancy and dislocation formation derived from po sitron annihilation lifetime measurements and the hyperfine magnetic charac teristics obtained from Mossbauer phase analysis. It has been found that an addition of Cr and Nb increases the thickness of the oxide Al2O3 surface l ayer 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. (C) 2000 Elsevier Science S.A. All rights reserved.