Dynamic tension and constitutive model in Fe40Mn20Cr20Ni20 high-entropy alloys with a heterogeneous structure

Abstract

Face-centered-cubic (FCC) Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) with a weigh of 50 Kg were fabricated by industrialized vacuum-induction melting. This alloy consists of a tetragonal σ phase and minority M23C6 carbides embedded in the continuous FCC matrix after thermomechanical treatments. A heterogeneous structure composed of a phase distribution and grain size is formed. The yield strength and ultimate tensile strength are increased from 398 MPa to 679 MPa at 10−4 s−1 to 743 MPa and 1412 MPa at 3000 s−1, respectively. Meanwhile, the elongation is slightly improved as the strain rate rises. The strain rate sensitivity under quasi-static tension is 0.0172, in contrast to 0.3978 under dynamic deformation. Upon dynamic tension, the simultaneous enhancements of both strength and ductility are attributed to the joint activation of multiple strengthening mechanisms. Deformation-induced twinning further improves the strain-hardening ability of the alloy. Besides, short range order may seriously hinder the dislocation movement, especially when the thermal activation of dislocations gradually fails at high strain rates, which limit the dislocation slip to a smaller scale and result in deformed sub-grains. In contrast, under quasi-static tension, only dislocation slip dominates, accompanied by dislocation entanglement and massive pile-ups. Moreover, a typical Johnson-Cook model was employed to predict the dynamic-flow behavior. This study sheds lights on the mechanical performance superiority from heterogeneous HEAs under dynamic tension and might open new insights for developing high-performance HEAs to resist dynamic impacts.