Evolution of microstructure, mechanical properties and phase stability of CoCrFeMnNi high entropy alloys

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability.