400 degrees C aging embrittlement of FeCrAl alloys: Microstructure and fracture behavior

Abstract

Two commercial advanced powder-metallurgical FeCrAl alloys with nominal composition of Fe-22Cr-6Al (APM) and Fe-21Cr-5Al-3Mo (APMT) were aged at 400 degrees C up to 4828 h. In the as-received condition, both alloys had similar amount of Al-rich particles, while there were more Si-rich particles in APMT. In the aged condition, APMT was more susceptible to the aging embrittlement than APM, showing a complete cleavage fracture in tensile tests. During aging, areal fraction and size of Si-rich particles were not affected for both alloys, but the growth of oxygen-free Al-rich particles was observed for APMT. Meanwhile, Fe-Cr phase separation was not observed in both alloys after 4828 h aging at 400 degrees C. Instead, fracture surface observation revealed that the severe aging embrittlement of APMT could be correlated to the growth of large Al-rich particles, which acted as crack initiation sites leading to the cleavage fracture.