Molecular Dynamics Study Of The Atomic Structure And Properties Of Entropy Alloys In NiCoCr

Since the concept of High entropy alloy(HEA)was proposed,the structure and mechanics of High entropy alloy(HEA)have been studied deeply.Structures of the HEA alloy are not complicated due to their multiple elements.On the contrary,they are simple solid solution structure,such as Body-Centered Cubic(BCC),Face-Centered Cubic(FCC),Hexagonal Close-packed(HCP)and mixed structure.High entropy alloy(HEA)has a unique structure,which makes it show very superior physical and chemical properties.Based on the discovery of high entropy alloy(HEA),medium entropy alloy(MEA)began to attract a large number of researchers because of its special structure and properties.Therefore,the study of the structure is of great significance for understanding the relationship between the structure and properties of high and medium entropy alloys.In this paper,the NiCoCr medium entropy alloy was selected as the research object.The atomic structure,kinetic properties and alloy properties of NiCoCr alloy were investigated by classical molecular dynamics method.Firstly,the effects of cooling rate and pressure on the structure of NiCoCr alloy were investigated.The effect of high pressure on the structure of NiCoCr alloy was studied.Finally,the effect of chemical order on mechanical properties of NiCoCr alloy was investigated.The effects of cooling rate and pressure on the structure of NiCoCr alloy were investigated by molecular dynamics simulation software.Firstly,the cooling process of NiCoCr alloy at different cooling rates was investigated.The crystallization temperature increased with the decrease of cooling rate.The liquid structure has enough time to nucleate and grow up,which makes the content of crystal structure increase.The result of pair distribution function for NiCoCr alloy at different cooling rates shows that the bonding force between Ni-Ni atoms is very strong,and the bonding force between atoms increases slightly with the decrease of the cooling rate.The analys of bond pair shows that the number of 1421,1422 and 1431 bond pairs is large in NiCoCr alloy,and the number of these three bond pairs increases with the decrease of cooling rate.The coordination number analysis showed that the coordination number decreased slightly with the decrease of cooling rate.Then,the cooling process of NiCoCr alloy under high pressure was investigated.It was found that the crystallization temperature increased with the increase of pressure.The result of pair distribution function for NiCoCr alloy shows that the bonding force and stucture become stronger and tighter.The coordination number analysis shows that Cr-Cr atoms are tend to separate,and the tendency increased with the increase of pressure.The investigation of NiCoCr alloy with different crystal types showed that the melting points of FCC-NiCoCr and HCP-NiCoCr crystals are 1400K and 1440K,respectively.The stability of NiCoCr alloy was investigated by establishing a NiCoCr model.The result shows that the HCP structure is low-temperature stable phase and FCC structure is high temperature-stable phase.The effect of high pressure on the structure and dynamic properties of NiCoCr melt was investigated.The first peak of the pair distribution function is used to characterize the strength of interatomic.The result shows that the bonding force of NiCoCr melt increases with the increase of pressure.The coordination number analysis shows that the coordination number of the melt increases when the pressure increasing.Bond pair analysis shows that the content of saturated bond pairs,such as 1551,1441 and 1661,increases whith the pressure increasing.The kinetic properties of NiCoCr melt was characterized by the mean squared displacement(MSD),self-intermediate scattering function(SISF),diffusion coefficient,relaxation time and diffusion activation energy.It was found that the diffusion coefficient decreased,the relaxation time increased and the diffusion activation energy increased with the pressure increasing.These results indicate that the atomic movement ability of NiCoCr melt weakens under high pressure.Finally,the influence of chemical order on the properties of NiCoCr alloy was explored.The degree of chemical order for NiCoCr alloy was characterized by the information entropy,and the yield strength of NiCoCr alloy increases with the decrease of information entropy.Further investigation shows that the Cr atom ratio affects the mechanical properties of NiCoCr alloy in the NiCoCr chemical structure.The local structure is difficult to deform when the number of Cr atoms in the coordination atom of the central atom is low.