The First-principle Studies On Mechanical Properties Of AlFeCrCuX High Entropy Alloys

The high entropy alloy was discovered and named in 1990s,it has broken through the traditional alloy design concept of one or two elements,which has become one of the hotspots in material research in recent years.The high entropy alloys are alloys formed by mixing five alloys at least in equiatomic or nearly equiatomic proportions.The high entropy effect produced by the mixing of multiple principal elements makes the high entropy alloy a simple cubic crystal structure and therefore have many excellent properties,such as high work hardenability,high hardness,high temperature softening resistance,corrosion resistance,high temperature oxidation resistance,high resistivity,and so on,without having to form a complicated phase or an intermetallic compound.Recently it is found that some of the more simple hexagonal structure of the high entropy alloy.However,the most research on high entropy alloy were supported by laboratories and do some work on high entropy alloy about phase composition,performance measurement and design,the research on high entropy alloys is limited.In this paper,the crystal model of AlFeCrCuX(X + =CoNi,TiZn)high entropy alloy is established by virtual crystal approximation.Using CASTEP software based on the first principle of density functional theory,two typical high entropy alloys AlFeTiCrZnCu and AlCoCrCuFeNi are lculated about structure and stability,elasticity and plasticity.It was found that the more atomic species,the lattice parameter was smaller,the mass density was higher,which indicate that the element of high entropy alloy are more and the binding energy were higher,and the stable were more stable.Each atom content of high entropy alloy also had an impact on its structure,the lattice parameter increased but the mass density decreased with Al,Ti,Cr increasing,and the lattice parameter decreased but the mass density increased with Fe,Ni increasing.The ground state total energy and heat of formation for AlFeCrCuX(X=CoNi,TiZn)high entropy alloy were calculated.The ground state total energy reflects the stability of the system,the heat of formation determined the thermodynamic stability of high entropy alloy.As seen from the calculated results,it is found the ground state total energy of AlFeTiCrZnCu hexanary alloy is minimum and the system stability is the best.It can be seen from the calculated results that the heat of formation was all negative except for AlFeTiCrZn quinary alloy,it indicated that the thermodynamic properity of high entropy alloy was stable,and the change of element content and pressure does not change the thernnodynamic stability of the high entropy.High entropy alloys occur structural phase transition under a very high pressure,so they are very stability with higher pressure.The elastic properties of AlFeCrCuX(X=CoNi,TiZn)high entropy alloy are calculated with elastic constant,Young’s modulus,bulk modulus and shear modulus.The mechanical stability and ductility/malleability of the high entropy alloy can be determined by the calculated elastic modulus.Young’s modulus,bulk modulus and shear modulus calculated by VRH approximation can also get the Poisson’s ratio and the ratio of the share modulus to bulk modulus of the high entropy alloy,which can determiine the brittleness and ductility of the high entropy alloy.The plastictiy of face cubic crystal AlxCoCrCuFeNi high entropy alloy is mainly explained by calculated the generalized stacking fault energy and the generalized stacking fault energy curve in the dislocation mechanism.In addition to the calculated the non-stable fault energy and the intrinsic stacking fault energy in the dislocation mechanism,the ratio of these two is also important to explain the dislocation mechanism.In order to describe the dislocation distribution,P-N model is also introduced,the Peierls stress and yield strength of AlxCoCrCuFeNi high entropy alloy are calculated.