Origin of properties in high entropy alloys

Abstract \nThe novel class of alloys known as high entropy alloys (HEAs) present two \nfundamental problems; 1) prediction of their properties and reaction to alloying \nadjustments, 2) prediction of compositions capable of forming the random solid \nsolution with simple crystal structure that appears to be key to their behaviour. \nHere DFT is applied to model the electronic structure of HEAs based on the \nCoCrFeNi pseudo base metal. This approach explains a number of properties such as \npreferred crystal structure and allows fundamental properties such as elastic moduli to \nbe calculated accurately. The stability of HEAs is discussed and compared to that of \nbulk metallic glasses and a composition is produced which is capable of forming both \na glassy and high entropy solid solution phase. A simple thermodynamic model is \nproposed to allow likely HEA solid solution forming compositions to be identified. \nThis modelling approach using both DFT and thermodynamics is used to assess two \npotential high entropy alloys based on light metals. \nThe approach shows that the electronic structure of HEAs may be used to predict their \nproperties and therefore their behaviour is due to a free electron structure, it also \nsuggests that the most important consideration in their stability as solid solution alloys \nis a lack of strong covalent interactions, ie a close to zero entropy of mixing.