Effect of manganese on mechanical properties and deformation mechanism of CoCrFeNi high entropy alloys

In this study, the predominant mechanical properties and deformation mechanisms of CoCrFeNiMnx high entropy alloys (HEAs) were explored by using the molecular dynamics (MD) simulation. A uniaxial tensile process with different temperatures (100-700 K) and compositions of manganese (x = 0, 5, 10 and 20) were conducted. Besides, a circular defect was created on the CoCrFeNiMnx HEAs to investigate the damage tolerance of these HEAs. The equiatomic CoCrFeNiMn HEA performed a strongly temperature dependence. The ultimate tensile strength (UTS) was 4.83 GPa at 100 K, and was decreased with the temperature increased. Based on the dislocation distribution and von Mises strain results, the early stage deformation was governed by the 1/2 < 110 >-type dislocation slip. On the contrary, the grain boundaries glide was dominated the later stage deformation. In addition, the manganese content in this work was higher than the limit to form the face-centered cubic (FCC) single phase solid solution. Instead, hexagonal close-packed (HCP) and amorphous phases appeared, and thus decreased the strength of CoCrFeNiMnx HEAs. The Mn0 HEA showed the highest yield stress, UTS and Young's modulus, which were 4.9, 4.8 and 218.4 GPa, respectively. In addition, the damage tolerance of these HEAs was enhanced by the amorphous phase formation, which inhibited the propagation of cracks and improved the ductility. Based on the results, the Mn5 HEA presented the best damage tolerance than others.