High-entropy alloy near-surface hydrogen-induced nanotwin and spinodal decomposition promoting heterogeneous structure evolution

After hydrogen charging (AHC) of the high-entropy alloy (HEA) AlCoCrFeNi2.1, lots of slip bands and nanotwins appeared in the face-centered cubic (FCC) phase. In body-centered cubic (BCC) phase, dense short-range stacking faults (SFs) appeared around the Cr-rich nanophases, and some SFs intersected to form Lomer-Cottrell (L-C) locks. Besides, hydrogen-assisted spinodal decomposition was also observed in the near-surface region. Along the thickness direction of the specimen, the gradient hydrogen concentration and stress potential gradient drive the generation of microscopic defects such as vacancies, SFs, and dislocations. Hence, further movement of these defects leads to the formation of nanotwins and spinodal decomposition.