High-temperature plastic flow of a precipitation-hardened FeCoNiCr high entropy alloy

In this work, we systematically investigated flow behavior of a high entropy alloy (HEA) strengthened by coherent γ′ precipitates in the temperature range of 1023-1173 K. In contrast to the single-phase FeCoNiCrMn HEA, this precipitate-hardened alloy, i.e., (FeCoNiCr)94Ti2Al4, exhibited large reduction of the steady-state strain rate (by ~2 orders of magnitude) or drastic enhancement in flow stress, indicating significant improvement in high-temperature properties. Our results showed that the deformation could be divided into two regimes. At temperatures below 1123 K, coherent γ′ precipitates effectively blocked the dislocation motion, thus resulted in a threshold stress effect. Above 1123 K, however, γ′ particles dissolved and the deformation was controlled by the ordinary dislocation climb mechanism. In addition, we conducted transmission electron microscopy to characterize dislocation-precipitate interaction to provide microstructural evidences to support our conclusion of the specific deformation mechanisms in the two temperature regimes.