Simultaneous strengthening effect of local chemical ordering and twin boundary on the medium entropy alloy CoCrNi

The interactive strengthening effect of twin boundary and local chemical ordering (LCO) structure in CoCrNi medium-entropy alloy (MEA) was investigated using molecular dynamics (MD) simulations of na-noindentation. The correlation between the two strengthening effects and the hardness was characterized. Meanwhile, underlying strengthening mechanisms were revealed. Results demonstrate that both LCO and twin boundary enhance the hardness of CoCrNi MEA. A concurrent strengthening effect appears when LCO and twin boundary are coupled for CoCrNi MEA with a stronger improvement on the hardness (12.40% at 70 K, 23.23% at 300 K, and 31.79% at 700 K). By comparing the plastic zones underneath the indentation, it is discovered that both LCO and twin boundary inhibit dislocation extension. The twin boundary provides a horizontal slipping path for dislocations. Moreover, since dislocations are pinned by Ni LCO structure on the twin plane, LCO can significantly limit the horizontal slip of dislocations on the twin plane.(c) 2022 Elsevier B.V. All rights reserved.