High‐Pressure and High‐Temperature Co‐Engineering of Dislocations and Chemical Short‐Range Order Mitigates the Strength–Ductility–Corrosion Trade‐Off in CoCrNi Medium‐Entropy Alloy
Cheng Ma, Lin Guo, Jianhong Yi, Ji Gu, Yilong Dai, Kecheng Long, Jianguo Lin, Min SongABSTRACT
Conventional processing makes it difficult to develop chemical short‐range order (CSRO) while retaining a high dislocation density in CoCrNi medium‐entropy alloy. Annealing promotes local ordering but accelerates dislocation recovery, whereas deformation introduces dislocations without producing a comparable ordered state. Here, high‐pressure and high‐temperature (HPHT) treatment at 5 GPa and 600°C for 2 h yields 1.3 ± 0.3 nm CSRO domains (projected area fraction, 26.9 ± 3.2%) and a dislocation density of (6.8 ± 0.3) × 10 13 m −2 without appreciable grain‐size change. First‐principles calculations show that pressure favors the ordered configuration through a negative ordering volume and raises vacancy formation enthalpy, limiting recovery. This architecture raises yield strength from 326 to 537 MPa and ultimate tensile strength from 800 to 880 MPa while retaining ∼72% elongation. Dislocations dominate the initial strengthening, while nanotwinning, microband formation, and deformation‐induced phase transformation develop within the HPHT‐induced dislocation–CSRO architecture. The same architecture also accelerates Cr‐dominated primary passivation in 0.1