Study On Nanoindentation Response Of High Entropy Alloy Based On Molecular Dynamics Simulation

After a long alloying process,the material is endowed with desirable properties.The traditional alloying process usually involves the addition of other trace elements to the total of the major elements.Recently,however,a new method of alloy design has emerged,in which a variety of main elements are mixed together in relatively high concentrations,typically between 5% and 35% of each element.Materials formed in this way are called high-entropy alloys.This new alloy strategy forms a sharp contrast with the traditional alloy strategy,so it has attracted extensive attention.Good oxidation resistance and excellent mechanical properties give high entropy alloys the ability to be used in future industrial fields.Nanoindentation testing technology is a commonly used method to measure the mechanical properties of small volume samples,which can obtain the mechanical properties of samples.However,the current level of science and technology is not enough to support on-site observation of the microstructure evolution of materials in the process of indentation,so we need to use computer-aided way to explore the movement process of atoms under the action of the indenter.Fe Co Cr Ni Cu,as a typical face-centered cubic high entropy alloy,has good oxidation resistance at high temperature,but the relationship between its mechanical properties and microstructure has not been revealed.In this paper,Fe Co Cr Ni Cu nanoindentation model is constructed based on molecular dynamics simulation method,and the interaction between atoms in the indentation process is simulated by NVT ensemble and velocity scaling method.It is found that the interaction between dislocation and solution brings about a high dislocation density during the indentation process of single crystal Fe Co Cr Ni Cu resulting in work hardening.According to the shear strain,atomic displacement and microstructure evolution,the slip systems in Fe Co Cr Ni Cu are abundant and the dislocation rings are active,which makes the high entropy alloy have good ductility.Through the dislocation density and stress-strain curve evolution analysis,it is found that the dislocation strengthening and lattice distortion strengthening occur during the deformation of the single crystal Fe Co Cr Ni Cu,which reveals the origin of the high entropy alloy with high strength.It is found that under the action of lattice distortion,the dislocation movement is hindered in the indentation process,which improves the strength of high entropy alloy.In order to further explore the influence of material structure on the mechanical properties of high entropy alloy,the effect of twin thickness and twin boundary on the deformation behavior of Fe Co Cr Ni Cu is investigated.The results represent that when the twin thickness is between 19.5 A and 28.9 A,the strength decreases with the decrease of the twin thickness,because the twin partial slip gradually dominates the deformation behaviors of the nanotwinned Fe Co Cr Ni Cu,presenting the inverse HallPetch effect.When the twinned thickness range is around 19.5 A,there is a certain twinned thickness where the strength of nano-twinned Fe Co Cr Ni Cu reaches the minimum critical value.High entropy alloys have great potential in future industrial applications.This paper reveals the quantitative relationship between microstructure and Fe Co Cr Ni Cu,which provides valuable reference for the design of advanced alloys.