Deformation Behavior of Fe-Al Single Crystals Containing Fe2AlTi Precipitates

Abstract

Fe-20Al-5Ti (at.%) single crystals composed of the bcc Fe-Al matrix and the Fe2AlTi precipitates with the L21 structure was examined. In the single crystals furnace-cooled (FC) from 1373 K to room temperature, coarse Fe2AlTi phase about 300 nm in diameter were precipitated in the bcc matrix. A misfit strain and a dissolution temperature of the L21 precipitates are +0.59% and 1151 K, respectively. The single crystals exhibited high yield stress above 600 MPa up to 973 K while further increase in temperature resulted in a decrease in yield stress due to the dissolution of the precipitates. In the FC crystals, 1/2<111> dislocations in the bcc matrix bypassed the coarse L21 precipitates due to their large misfit strain, resulting in high strength. In contrast, the fine L21 precipitates about 30 nm in diameter were observed in the crystals after solutionization and annealing at 873 K. The crystals with the fine L21 precipitates demonstrated high yield stress above 1100 MPa at and below 773 K. Uncoupled or paired 1/2<111> dislocations cut the fine L21 precipitates, leaving an anti-phase boundary (APB) inside the precipitates. The APB inside the precipitates was considered to be responsible for strong precipitation hardening.