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.