Nanoindentation into a dual-phase bicontinuous lamellar high-entropy alloy

The plastic response of a dual-phase high-entropy alloy to nanoindentation is studied using molecular dynamics simulation. The sample has a bicontinuous lamellar structure consisting of an equiatomic FeNiCrCo fcc phase and an Al 50 (FeNiCrCo) 50 bcc/B2 phase. Its large size ( > 28 million atoms) allows comparison of indentations into a fcc lamella, a bcc lamella and on an fcc/bcc interface. In addition, the lamella thickness of 20–30 nm allows for extensive dislocation plasticity both in the fcc and the bcc phase. We find that the hardness of the alloy at the interphase boundary is not a simple average of the hardness of the lamellae. The plasticity is mostly dislocation controlled, and twinning is relevant only in the fcc phase. Phase transformations do not occur and – in contrast to previous studies – even amorphization is negligible. Dislocation pile-ups are observed in the fcc phase next to the interface. Shear strain is not easily transmitted – in the form of dislocations or stacking faults – across phase boundaries.