Liangbin Chen, Ke Tang, Weijie Tian, Ran Wei, Yaohui Li, Yanpu Chao, Feng Jiang
Heavy carbon doping is an effective strategy to enhance the mechanical properties of face-centered cubic (FCC) medium/high-entropy alloys (M/HEAs), but often induces ductile-brittle transition (DBT) at cryogenic temperatures, restricting their cryogenic applications. Herein, the (Fe 40 Mn 40 Co 10 Cr 10 ) 96.7 C 3.3 MEA was prepared and cold rolled at room temperature to pre-introduce deformation into microstructure to avoid the cryogenic DBT behavior. Furthermore, the effects of cold rolling reduction and temperature on the mechanical response, deformation mechanisms and fracture characteristics were systematically investigated. The results show that the MEA maintains a single FCC phase without phase transformation during cold rolling and subsequent tensile deformation. At 298 K, the alloy exhibits a typical strength-ductility trade-off, i.e., yield strength increases linearly from 476 MPa to 1279 MPa, while fracture elongation decreases from 70.1% to 12.6%, accompanied by a fracture mode transition from shear to normal fracture with increasing cold rolling reduction. In contrast, at 77 K, the alloy manifests a non-monotonic ductility evolution, that is, fracture elongation first decreases to 12.7% at 20% rolling reduction but rises to 26.5% at 30% rolling reduction, achieving superior strength-ductility synergy (yield strength: 1625 MPa), which is attributed to the extensive activation of deformation twins that not only accommodate plastic strain, but also suppress strain localization, effectively transforming the fracture mode from intergranular to transgranular fracture. Quantitative analysis of strengthening mechanisms reveals that dislocation strengthening and twin boundary strengthening are the dominant contributors to yield strength. This work demonstrates that opportune pre-deformation is an effective approach to tailor the deformation mechanisms and inhibit cryogenic brittleness for carbon doped M/HEAs.