Twinning and 9R Phase Transition Mediated Extraordinary Cold‐drawn Deformability in NiCoCrFeMo High‐Entropy Alloy

Abstract

The production and application of materials are evolving towards the low‐dimensional micro‐nano scale. Nevertheless, the fabrication of micron‐scale alloy fibers remains a challenge. Herein, a novel Ni‐Co‐Cr‐Fe‐Mo high‐entropy alloy (HEA) fiber with a cold‐drawn reduction rate of 99.9995% and a strain (ɛ) of 12.19 is presented without requiring intermediate annealing. The exceptional deformation strain of 11.62 within the fiber leads to extraordinary tensile strengths of 2.8 GPa at room temperature and 3.6 GPa at 123 K. The in‐depth investigation of the microstructure of fibers has revealed the cold drawing deformation mechanisms mediated by the synergistic effects of plane defects. Specifically, various geometrically necessary dislocation interfaces, such as dislocation walls and microbands, along with deformation twins and long‐period 9R structures, form in response to external stress when ɛ≤2.7. As the strain increases, the saturated layered structure emerges and progressively evolves into a 3D equiaxed crystal. Moreover, the formation and evolution of the 9R structure (i.e., the migration of incoherent twin boundaries), coupled with the interaction of partial dislocations and the role of deformation twins, are crucial factors determining the fiber's plastic response. This work provides a novel approach to discovering new high‐strength metallic fibers with excellent deformability through plane defects engineering.