Microstructure tailoring to enhance mechanical properties in CoCrFeNiMn high-entropy alloy by Ti addition and thermomechanical treatment

Highlights: • Single-phase CoCrFeNiMnTi_0.1 and CoCrFeNiMnTi_0.3 HEAs were processed by thermomechanical treatment. • Adding Ti to CoCrFeNiMn promotes thermal stability of precipitates and postpones recrystallization and grain growth. • Cr-rich bcc, Cr-rich σ and Ni₃Ti- precipitates were detected in the CoCrFeNiMnTi_0.3 HEA after annealing. • Adding Ti combined with thermomechanical treatment provide a good combination of strength and ductility in CoCrFeNiMn. CoCrFeNiMnTi_x (x = 0.1 and 0.3) high-entropy alloys (HEAs) were processed by thermomechanical treatment including heavy cold rolling followed by post-deformation annealing (PDA) at 773 to 1173 K for up to 60 min. Microstructural evolutions by adding titanium and thermomechanical treatment revealed significant enhancement in the mechanical properties with combination of high strength and ductility in CoCrFeNiMn HEA. The initial microstructures consisted of a single fcc phase while the PDA led to formation of complicated microstructure due to precipitation and recrystallization. The results indicated that adding titanium promoted thermal stability of precipitates and postponed coarsening by solute drag and Zener pinning. The CoCrFeNiMnTi_0.3 HEA showed high strength even after PDA at 1173 K due to stability of precipitates at this temperature. However, similar procedure resulted in dissolution of precipitates which facilitated coarsening and reduce the strength significantly in the CoCrFeNiMnTi_0.1 HEA. The latter alloy showed remarkable mechanical properties with an ultimate tensile strength (UTS) and elongation to failure of ~900 MPa and ~ 30%, respectively, after PDA at 973 K.