Short-range-ordering strengthening and the evolution of dislocation-nucleation modes in an Fe40Mn20Cr20Ni20 high-entropy alloy

Compared with the Fe40Mn20Cr20Ni20 high-entropy alloy in a homogenized state, it has higher incipient plastic strength after high-temperature aging, which is attributed to the generation of short-range orderings (SROs) caused by the local composition fluctuations. Based on nanoindentation results at different loading rates, the evolution trends of homogeneous and heterogeneous dislocation-nucleation modes under the effect of SROs are revealed. Under the action of the high-solution friction stress, which is caused by the high loading rate, and coherency-strain field, which is caused by SROs, the critical shear stress of the dislocation nucleation increases. Furthermore, with the increase of the loading rate, the probability of heterogeneous nucleation in homogenized samples increases, while that in aged samples is the opposite. From the perspective of the distribution of dislocation-nucleation sites, this opposite trend can be well explained by assuming the spreading resistance of an activatable region. In short, the present work reveals the pivotal role of SROs on dislocation-nucleation modes and paves the way for the quantitative study concerning SROs and their strengthening effects.