Influences of strain rate, Al concentration and grain heterogeneity on mechanical behavior of CoNiFeAl_xCu_1-x high-entropy alloys: a molecular dynamics simulation

High-entropy alloys (HEAs) with a heterogeneous grain structure have been revealed to possess excellent combination of strength and toughness. However, the atomic-level deformation mechanisms of the heterogeneous HEAs were not reported yet. In this work, physical models were constructed based on the experimental observation and atomic simulations are performed to investigate the tensile behavior of face centered cubic (FCC) heterogeneous CoNiFeAl_xCu_1-x HEAs at different strain rates (5 × 10⁷–1 × 10¹⁰ s⁻¹), Al concentration (x = 0.1, 0.2, 0.3 and 0.4) and degrees of grain heterogeneity. Result analysis reveals the multiple deformation mechanisms including dislocation motion, diffusion from grain interior to grain boundary and stacking faults (SFs) as well as their interaction. The strain rates seriously influence the body centered cubic (BCC) transformation from FCC in the large grains. Besides, with the reduction of Al concentration, the value of stable stacking fault energy (SFE) raises, while the tensile yield stress increases. Finally, increasing the large grain size (D_G) of the heterogeneous grain structure improved the plasticity due to the combination of enhanced FCC to BCC phase transformation and high uniform ductility of large grains. This work provides a micromechanical understanding for designing the excellent mechanical property of HEAs by optimizing material structure parameters of heterogeneous grain structure HEAs.