Role of Local FCC Structure to the BCC Polycrystalline NbMoTaWV High‐Entropy Refractory Alloy under Plastic Deformation

Abstract

The molecular dynamics (MD) simulation is used to explore the role of local face‐centered cubic (FCC) structure to the body‐centered cubic (BCC) polycrystalline Nb20.6Mo21.7Ta15.6W21.1V21.0 refractory high‐entropy alloy under plastic deformation. With the grain size of 25.3, 27.9, and 31.9 nm, the dislocation propagation within grains at strains larger than the ultimate strain is the dominant deformation mechanism. With the grain size of 20.1 and 15.6 nm, the dislocation propagation within the grain and the local structural transformation from BCC to the undefined type at the grain/grain boundary (GB) interface are two main deformation mechanisms. With the grain size of 10.0 and 5.2 nm, the local BCC structures of grain atoms significantly become the undefined type, which is the main deformation mechanism during the tensile process. The FCC fraction increases from yield strain to ultimate strain, and remains a FCC fraction of the highest value, indicating the role of local FCC structure is more significant for the cases without dislocation deformation mechanism. Once a large amount of BCC atoms is transformed into the undefined type, some BCC atoms need to transform into local FCC atoms for making their neighbor BCC atoms more local space to decrease the energy barrier for the BCC transformation to the undefined type.