Effect of Mo and Ni elements on microstructure evolution and mechanical properties of the CoFeNixVMoy high entropy alloys

A series of CoFeNiVMoy (y = 0-1) and CoFeNixVMo (x = 1-2) high entropy alloys were designed in order to study the effect of Mo and Ni elements on their microstructure evolution and mechanical properties. Results show that for the quinary CoFeNiVMo alloy, by either decreasing the Mo content to 0.6 or increasing the Ni content to 1.4, eutectic microstructures can be obtained. For the CoFeNiVMoy alloys, with increasing Mo content, the volume fraction of the CoMo2Ni-type intermetallic phase increases which results in a decrease of the plastic strain and an increase of the yield strength, and the Vickers hardness shows an approximately linear increase from HV 238.1 to HV 624.6. While for the CoFeNixVMo alloys, with increasing Ni content, the increased FCC solid solution phase leads to an increase of the plastic strain and a decrease of the yield strength. Among these alloys, the CoFeNiVMo0.2 alloy shows the best comprehensive compressive properties: high yield strength of 686.9 MPa and ductility above 80%. In addition, the formation condition of eutectic HEAs was also investigated. It is found that the parameters of valence electron concentration (VEC), atomic size difference (delta), enthalpy of mixing (Delta H-mix), entropy of mixing (Delta S-mix) and electronegativity (Delta chi) cannot effectively design the composition of eutectic HEAs. (C) 2015 Elsevier B.V. All rights reserved.