Mechanical Properties Of Al_xCoCrFeNi High-Entropy Alloy:A Molecular Dynamics Study

High entropy alloy is a new alloy developed in recent years.Its characteristics of high wear resistance,high strength and hardness make it have a broad application prospect.In the process of exploring high entropy alloys,it is more and more important to analyze the mechanism of excellent properties of high entropy alloys from the microscopic scale.The emergence of numerical simulation is a powerful supplement to the traditional theoretical and experimental methods.Molecular simulation plays an important role in revealing and predicting the properties of materials at atomic scale.In this paper,based on Al_xCo Cr Fe Ni high entropy alloy,molecular dynamics（MD）method was used to simulate the tension process of high entropy alloy at atomic scale,and its microstructure was analyzed.After calculating the stacking fault energy,we successively investigated the mechanical properties of single crystal,single crystal with pre-prepared twin boundaries,and polycrystal model under axial loading.In the single crystal,the effects of conventional tensile,different temperature and different Al content on the mechanical properties of the materials were investigated.Simulation results show that the Alx Co Cr Fe Ni undergoes elastic-yield-plasticity stages in sequence during the stretching process.After yielding,dislocation lines appear in the material,followed by stacking faults and twins.With the continuous generation and disappearance of dislocations,the material produces uneven plastic deformation.The analysis shows that the atomic radius difference between Al element and other elements produces lattice distortion effect,and the binding force with other atoms affects the Yang’s modality and yield stress of high-entropy alloy;the increase in temperature leads to increased thermal vibration between metal atoms,increased atomic dynamic energy,increased distance between atoms,and decreased binding force between atoms,resulting in a decrease in alloy elastic modality and yield stress.The net effect of temperature is similar to lattice distortion.In the single crystal with pre-prepared twin boundaries,the effect of co-crystal twin boundary（TB）spacing on uniaxial tensile deformation behavior of Al_0.1Co Cr Fe Ni high entropy alloy was investigated.Studies have shown that there is a"sensitive distance"between the twin boundaries,and the sensitivity of the two sides to the change of the twin spacing is different,and the influence of the evolution of the deformation mechanism of the different twin spacing is analyzed from the number of defects and the evolution of the dislocation density.In addition,as the distance between twins decreases,the deformation mechanism gradually transformation from dislocation slip accompanied by defects such as stacking faults and secondary twins to a deformation mode of amorphous phase transition.The research aims to provide guidance and reference for the design of high-performance high-entropy alloys.In the polycrystal,the effects of different strain rates on the mechanical properties of the materials were investigated.The simulation results show that the stack fault plays an important role in the tensile deformation process,and the FCC-BCC phase-transition occurs.The strain rate effect exists in the polycrystalline model,and the dislocation entangles with each other under high-speed loading,resulting in high-density dislocation cells and dislocation walls,which hinder the dislocation slip of atoms.In addition,as the thermal activation is weakened due to the high strain rate,the greater the resistance to dislocation slip,the stronger the interaction between dislocation and dislocation,resulting in a significant strengthening effect of the alloy.