Multi-principal element alloys with High-density nanotwinned 9R phase

Nanostructure design is an effective strategy for strength enhancement for metals and alloys. Nevertheless, stacking faults and nanotwins are not thermodynamically favoured. Here, it is demonstrated that high-density 9R phase with a columnar nanotwinned structure can be obtained through rational compositional design in a novel NiMnAlFeCr multi-principal element alloy. A combined density functional theory (DFT) study and molecular dynamics simulation (MD) was also performed to study the impact of alloy composition on the stability of 9R phase and its consequences on strength. The results showed that the energy barrier of formation of stacking fault can be obviously reduced by introduction of Fe or Cr in NiMn solid solution and its stability can be enhanced by simultaneously addition a certain range of Fe and Cr, which in favoring formation of high-density 9R phase.The experimental and simulation results demonstrate the substantial impact of 9R phase on the mechanical properties of the (Ni50Mn30Al20)100-x(FeCr)x alloys. This study provides a novel insight into nanotwinned structure as well as a promising strategy to design materials with high-strength.