Microstructure and Mechanical Properties of CrMnFeCoNi High-Entropy Alloys Produced by Warm Multi-Pass Caliber Rolling

Designing novel high-entropy alloys (HEAs) with low stacking fault energy has been drawn significant attention for achieving a unique combination of high strength and ductility via transformation-induced plasticity (TRIP) mechanism. However, extensive work hardening of TRIP HEAs have led to the difficulties in metalworking, which required very high thermomechanical processing temperature even to 1000 oC. In this study, we introduced warm multi-pass caliber rolling to Cr₂₀Mn₂₀Fe₂₀Co₂₀Ni₂₀ (Ni20) HEA and Cr₂₀Mn₂₀Fe₂₀Co₃₅Ni₅ (Ni5) TRIP HEA to validate the feasibility of thermomechanical processing for TRIP HEAs at 400 oC. Grain growth behavior of annealed HEA bars was analyzed after recrystallization and Vickers hardness test was performed to compare the Hall-Petch relationship for Ni5 and Ni20 HEAs. Ni5 TRIP HEA exhibited higher strain hardening but lower tensile elongation than Ni20 HEA, which was responsible for the poor workability of Ni5 TRIP HEA at room temperature. Tensile tests in temperature range from -180 to 225 oC revealed that Ni5 TRIP HEA showed stress-induced martensitic transformation that had preceded slip deformation of the austenitic phase in 10 – 100 °C, which is the temperature range feasible for shape memory applications. These results demonstrate that the warm multi-pass caliber rolling can be an effective process to fabricate TRIP HEA billets for structural and functional applications.