Cooperative grain boundary sliding in creep deformation of FeCrAl-ODS steels at high temperature and low strain rate

The high-temperature deformation mechanism of the FeCrAl-ODS ferritic steel was investigated at 1000 degrees C for the creep loading perpendicular to the elongated and aligned grains. The strain rate was varied in the range from the order of 10(-2) to 10(-7) s(-1). With decreasing strain rate from 10(-2) to 10(-5) s(-1), creep mechanism shifts from conventional dislocation creep pinned by oxide particles to grain boundary sliding (GBS) assisted concomitantly by diffusional creep. With further decreasing strain rate to 10(-7) s(-1), deformation mechanism is drastically changed; group of three grains can move cooperatively, and cooperative GBS (CGBS) was originally recognized. The threshold stress for onset of CGBS was designated as sigma(I)(th) (CGBS). Rate limiting process of CGBS is dominated by dislocation movement over the oxide particles so as to relieve the stress accumulation due to CGBS. The sigma(I)(th) (CGBS) for CGBS corresponds to one third of the conventional threshold stress for dislocation creep. (C) 2018 Elsevier B.V. All rights reserved.