Atomistic simulations of deformation mechanism of fcc/bcc dual-phase high-entropy alloy multilayers

Dual-phase nanoscale lamellar microstructures containing alternating regions of soft phase and hard phase are known to produce alloys with an exceptional combination of strength and plasticity. Here, the effect of layer thickness on the mechanical properties and deformation mechanism of the fcc/bcc dual-phase CoNiFeAlxCu1-x high-entropy alloys multilayers are investigated by the molecular dynamics simulation method. The results show that the deformation behavior of the multilayers is strongly related to the layer thickness. At the yield point, the deformation behavior of the small thickness multilayer is caused by the dislocation slip in the fcc phase, while the plastic deformation of the large thickness multilayer is initiated by the bcc → hcp phase transformation in the bcc phase. During the subsequent plastic deformation, the phase transformation of bcc → fcc also occurred in the bcc phase of the multilayer, which depended on the relative size of the bcc phase in the multilayer. Especially for the multilayer with the layer thickness of 2 nm, the bcc → fcc phase transformation promotes the formation of twins, and the fcc/bcc phase interface transforms into a perfect twin boundary. The twin formation mechanism and phase transformation mechanism are also discussed in detail.