Microstructural evolution and yield strength of a novel precipitate-strengthened Fe-based superalloy during thermal aging at 700 °C

Abstract

Microstructures and compressive yield strength of a novel γ′-strengthened Fe-based superalloy with about 55 wt% iron are investigated after aging at 700 °C for various durations. We found that the γ′ particle always displays a spherical shape and its size increases only from 9 ± 1.6 to 51 ± 14.0 nm with increasing the aging time up to 10,000 h. Meanwhile, the distribution of carbides at grain boundaries is always discontinuously, and no topologically close-packed phases are visible in the alloy during aging. Compressive deformation tests disclose that the yield strength of the experimental alloy at 700 °C increases firstly and then decreases with particle size. Microstructural observations uncover that the predominant deformation mechanism changes from shearing of γ′ particles by weekly-coupled dislocations to shearing by strongly-coupled dislocations and then to Orowan looping with enlarging particle size at the beginning of plastic deformation. Based on these results, it is deemed that the evolution of microstructure and deformation mechanism with aging time leads to the changes in the yield strength during thermal aging.