Geometrical Thermodynamic Investigation on Fe-Co-Ni(Mn-Si) x High Entropy Alloys And Correlation with Their Structural and Magnetic Properties

In the present study, different symmetrical and asymmetrical geometrical thermodynamic models such as Muggianu, Lück chou, Kohler, Colinet, Hillert, Toop, General solution model (GSM) were modelled by using the Redlich-Kister formalism for all the possible binary alloy system and then applied to FeCoNi(Mn-Si)_x (x=0.0,0.1,0.25,0.5,0.75,1.0) HEAs at 1273 K (FCC phase). The results revealed that asymmetrical GSM model with a similarity coefficient ξ_(ij)^(k) of ~0.5 shows maximum negative excess Gibbs free energy (G_1-2-^E_3-4-5) and associated activity coefficients (Υ_a) decreases with the elevation of excess energy as well as Mn-Si content. The Miedema semi-empirical model was also evaluated in order to confirm the G_1-2-^E_3-4-5 and associated Υα greatly influenced by a high negative value of enthalpy of mixing (ΔΗ_mix) and melting temperature (T_m). These negative value of ΔΗ_mix and G_1-2-3^E_-4-5 plays a significant role during the formation of the solid solution produced by non-equilibrium process i.e. mechanical alloying (MA). Therefore, an experimental approach has been carried out in the proposed alloy system on the basis of phase evolution, physical parameters such as lattice parameter (LP), crystallite size (D_crystal), microstrain (ε_s) and dislocation density (ρ_dis), microstructure and magnetic properties were performed at 300 K.