Serrated flow stress and nano-precipitation in (CoCrFeNi)94Ti2Al4 high entropy alloy

(CoCrFeNi)94Ti2Al4 high entropy alloy (HEA) was fabricated through drop-casting and conventional thermo-mechanical processing. After cold rolling and recrystallization heat treatments, the tensile properties were investigated at room temperature (RT), 573 K, and 873 K, respectively. At RT, the stress-strain curve exhibits non-serration. However, with the increasing tensile temperature from 573 K to 873 K, the serration evolves from type A + B to type C, and the maximum stress drop rises from 15.0 MPa to 24.7 MPa. At 873 K, C-type serration first appears at the yield strain, but finally disappears when the plastic strain above 12%. Transmission electron microscopy (TEM) analysis indicates that the simultaneous effects of twinning boundary and high density dislocations promote the dynamic precipitation of nanoscale L21-Heusler phase during tensile deformation. •The dynamic precipitation and its effects on serrated flow stress has been investigated for (CoCrFeNi)94Ti2Al4 alloy.•The gliding dislocation is severely piled up at the twinning boundary during tensile tests.•Twinning boundary is the preferential nucleation site for Heusler phase.•A large amount of stacking faults network is formed during plastic deformation.