Study On Melting Mechanism And Melt Transport Behavior Of CoCrFeMnNi High-Entropy Alloy

Multicomponent alloys exhibit many unique properties that are different from traditional alloys because of the diverse types of atoms they contain.The severe lattice distortion in the crystal structure leads to its slow kinetics and high phase stability.Many excellent properties have been obtained.At present,the research on multi-component alloys involves many aspects.Scholars from various countries have carried out a lot of exploration in all aspects from structure to performance.However,many of its basic properties,such as melting mechanism,interface properties and melt There is no clear theory for the properties,etc.For multicomponent alloys,in order to deeply understand the inherent atomic mechanism of their properties,it is necessary to know what role each component plays in it,because the elements that make up high-entropy alloys are in the element period.The positions in the table are relatively close,the atomic size does not change much,and distinguishing the similarities and differences of neighboring atoms at the subnanometer scale requires equipment with extremely high resolution capabilities,which cannot be achieved at the current level of human experiments.However,under the method of molecular dynamics simulation,we can easily separate various elements,which provides great convenience for our elemental research.The method of basic molecular dynamics studies the melting kinetics of multicomponent alloys,from the atomic mechanism of melting to the Lindemann melting theory of multi-component alloys.Melting is a topological order-todisorder transition where the crystal becomes disordered and turns into a liquid.In pure systems,melting is related to positional disordering only,whereas in multicomponent systems,it is affected by the chemical components.Here,we report a first investigation of this important open issue in homogeneous melting in a five component model system,or high entropy alloy,with a particular focus on the atomic mechanisms.We show that melting proceeds with several stages dictated by the low melting point component:Partial disordering starts at a much lower temperature below the bulk melting point with the low melting point element executing an exceedingly large atomic displacement.Instead causing melting,the displaced element catalyzes the formation of mobile atomic chains and loops that still conform to the crystalline lattice.With increasing temperature,other elements gradually participate in these highly correlated atomic configurations,causing their growth and proliferation,and eventual formation of the liquid phase.The detailed atomic process provides a direct support for the recently proposed melting mechanisms involving the atomic chains and loops,rather than the Lindemann critical vibrational displacements.In the study of the melting kinetics of multi-component alloys,the phenomenon of liquid nucleation in the system was found.The melting starts with the nucleation of liquid nuclei and the formation of critical nuclei,followed by spontaneous growth.As the temperature of the system continues to rise,the system will form a liquid core when it approaches the melting point.The size of the liquid core is distributed in an exponential shape and constantly fluctuates.As the temperature continues to rise,the small liquid core disappears,and the dominant core will continue to increase until the entire system melts.Aiming at the internal mechanism of liquid core formation,and how to understand the theory of liquid core formation,to explain these,we need to know the relevant information of the solid/liquid interface energy of the high-entropy alloy system.Since the solid and liquid phases are both condensed states,only experimental It is difficult to obtain the solid/liquid interfacial energy by means.Therefore,by establishing a physical model and by means of computer simulation,we discussed the interface dynamics of the CoCrFeMnNi high-entropy alloy system,and calculated the solid/liquid interface energy and anisotropy parameters of the CoCrFeMnNi high-entropy alloy system.The anisotropy parameter is much smaller than that of traditional alloys,and it is easier to nucleate,so this explains the nucleation mechanism of multicomponent alloys in the melting process from the perspective of energy.The alloy melt is a kind of "matrix" for the solidified crystal or amorphous of the alloy,so the internal micro structure of the alloy melt has a certain "heredity" to the crystal or amorphous microstructure of the alloy after solidification.,which has a great influence on the properties of solids,so the research on alloy melts has always been a field that researchers are keen on,and a very important aspect of the research on melts is the transport dynamics of melts,while melts The transport of,contains two mutually restricting objects:diffusion and viscosity.The larger the atomic diffusion coefficient in the melt,the faster the melt will diffuse,which proves that the faster the kinetic process,the smaller the viscosity.The smaller the viscosity coefficient,on the contrary,if the kinetic process of the system is slow,the viscosity of the melt will be large,and the corresponding diffusion coefficient of atoms in the melt will be small,so these two aspects are considered by EinsteinStow.Kess relationship is connected.Diffusion is a key kinetic factor determining chemical mixing and phase formation in liquids.In multicomponent systems,the presence of different elements makes it challenging to measure diffusivities and understand their mechanisms.Using a molecular dynamics simulation,we obtain the diffusion constants and the atomic process of a model Cantor alloy liquid made of five equimolar components.We show that the diffusivities conform remarkably well to the Arrhenius law in the wide range of temperature covering both the equilibrium and undercooled liquid region.The activation energies for all the alloy elements with different bonding energies and atomic sizes are close to each other.The results suggest that the diffusivity in the multicomponent liquid tends to be homogenized by the components with marginal differences.This allows us to treat the different elements as a single type of atom,the pseudo atom,for diffusional and maybe structural and physical properties in the multicomponent liquids.