Relationship Between Structure/Microstructure and Hardness of CrMnFeCoNiX0.5 High-Entropy Alloys with Refractory Metals X = V and Mo Obtained by Mechanical Alloying

The present study examined the interactions between the structure, microstructure and mechanical properties of CrMnFeCoNi, CrMnFeCoNiV0.5 and CrMnFeCoNiMo0.5 High-Entropy Alloys (HEAs). Starting from elemental powders, the HEAs were obtained by high-energy ball milling, followed by vacuum annealing at 1373 K for 1 h. After milling, a binary FCC-BCC solid solution was formed; the samples showed hardness values ranging from 800 to 973 HV. Evidence shows that annealing HEAs reduced the solubility of V and Mo in the alloys’ FCC structure. Additionally, the Cr content in the FCC phase also decreases. The carbon derived from the decomposition of the process control agent was trapped in the interstices of the HEA structure during mechanical alloying. This amount of carbon is sufficient to form carbides during annealing. The thermodynamic stability of the precursor elements in HEAs is a determining factor in MxCy-type formation. The hardness response of HEAs was associated with the HEAs’ structure, while the elastic modulus was affected by their microstructure.