The Properties Of Equi-atomic Medium And High Entropy Alloys By First-principles Calculations

It is generally believed that in high-entropy alloys?HEAs?,mixing entropy plays a leading role in thermodynamic stability.For the five-component face-centered cubic?fcc?CrMnFeCoNi HEA with equal composition,considering the brittleness and antiferromagnetic properties of Mn and Cr elements compared with Fe,Co and Ni,it is crucial to understand the bonding between atoms for the design of HEAs.First principle calculations based on density functional theory are carried out in this work,we study the magnetic properties,the bond between the Mn and Cr atoms and the vibrational,magnetic and electronic free energy in addition to the contributions related to configurational free energy.As described next,?1?Under spin polarization,covalent bondings are formed between the Mn and Cr atoms.Meanwhile,Cr atoms tend to couple neighboring ferromagnetic?FM?Co to themselves,resulting in Co moments being antiferromagnetically aligned,which is the opposite of the initial FM state.?2?Based on the analysis of the partial density of the states?PDOS?,the primary contribution to the total magnetic moment arises from the spin polarization of Fe d and Mn d states.?3?As the temperature is over 600K,the vibrational free energy exceeds the free energy of configuration.The contribution of magnetic free energy is about twice than that of electronic free energy in the finite temperature range,suggesting it plays an important role in the thermodynamic stability of HEAs.In view of observing the electron localization function?ELF?of the CrMnFeCoNi HEA,we further explored relationship among the ELF,the mixing enthalpy(?H_mix),the electronegativity difference??_??and the Zener anisotropy index?A_Z?of three-component AlCrFe,AlCoCr,AlCoFe,CoCrNi and CrFeNi medium-entropy alloys?MEAs?in the AlCoCrFeNi system.The results are as follows,?1?CoCrNi and CrFeNi adopts FCC structures are thermodynamically stable,and AlCrFe is body-centered cubic?BCC?structure,which are consistent with experimental observations.?2?For the MEAs of the FCC/BCC structure studied,we propose that the A_Z is positively correlated with the?_?,that is,the greater the?_?,the more obvious the anisotropy.?3?The charges are relatively local around the atoms with the minimum Pauling electronegativity???and valence electron concentration?VEC?.Furthermore,a higher localized of the charges corresponds to a more pronounced anisotropy.?4?By further analyzing the Bader electron transfer of atoms,we find that for the FCC/BCC structures,the larger the total electron transfer amount,the higher the degree of electron localization,resulting in the uneven distribution of the bondings and the greater anisotropy nature of MEAs.