Molecular Dynamics Simulation Microcrack Propagation Of Al_0.1CoCrFeNi High Entropy Alloy

The properties of high entropy alloys,such as high hardness,high strength,high tempering resistance,high oxidation resistance and high wear resistance,perfectly meet the requirements of today's society for the properties of metal materials,and have a good application prospect in nuclear,turbine,aerospace industry and other fields.However,defects such as vacancies and cracks will inevitably occur in the preparation and processing of high entropy alloys,which would limit tremendously the industrial application.Based on the molecular dynamic method,the evolution behavior and deformation mechanism of defects in the process of material crack propagation at nanometer scale are revealed in this paper.The cracks of Al0.1CoCrFeNi high entropy alloys are divided into I-type crack and II-type crack for tensile process,and the effects of different strain rates and vacancy equilibrium concentrations on the microstructure and mechanical properties of Al0.1CoCrFeNi high entropy alloys are studied.The main results are as follows:?-type crack in Al0.1CoCrFeNi high entropy alloys mainly focuses on the evolution of microstructure in tensile direction,dislocation emission and the change of alloys shape during tensile fracture.The crack tip emits dislocations along the directions of 45° and 135° degrees with the tensile stress,and dislocations formed by HCP and BCC structures are emitted and then piled up near the boundary.The alloys are obviously depressed at the position where HCP structures accumulate,that is,at the position of 1/3 of the alloys,and finally fracture occurs at the same position.The I-type crack in Al0.1CoCrFeNi high entropy alloys shows ductile fracture during the tensile process.With the increase of strain rate,the crack growth rate slows down,and the Young's modulus and yield strength increase.Compared with single crystal,the plastic deformation ability of Al0.1CoCrFeNi high entropy alloys with I-type crack with grain boundaries increases,the stress required for material yield decreases,and the yield strength also decreases.The tensile simulation results of Al0.1CoCrFeNi high entropy alloys with I-type crack show that the Young's modulus,yield strength and crack propagation of Al0.1CoCrFeNi high entropy alloys are consistent with the existing physical experiment results.?-type crack in Al0.1CoCrFeNi high entropy alloys mainly concentrates on the direction of dislocation slip and the change of stacking fault structure in the direction of crack propagation.During the tensile process,the crack tip of II-type crack in Al0.1CoCrFeNi high entropy alloys is constantly nucleated by dislocation,which is emitted to the boundary and piled up,resulting in stress concentration.However,the dislocation slip destroys the normal stacking order of local atoms in the crystal and forms intrinsic stacking faults.With the increase of strain rate,the yield strength of Al0.1CoCrFeNi high entropy alloys with II-type crack increases,which indicates that the increase of strain rate of the alloys will obviously affect the tensile mechanical properties of the material.Vacancy helps to alleviate the initial crack growth by amplifying the stress field around the crack tip.Compared with the alloys without vacancy,the alloys with vacancy have more severe passivation at the crack tip,which requires more strain to break atomic bonds and expand cracks.With the increase of vacancy content,the critical stress required for dislocation nucleation at the crack tip first increases and then decreases,which means that when there are a few vacancies in the alloys,it will hinder the dislocation movement.However,with the increase of vacancy equilibrium concentration,when the vacancies in the alloys begin to increase,the vacancy equilibrium concentration exceeds the critical value of hindrance.The existence of vacancies leads to the interaction between dislocation vacancies in the material,and the increase of vacancy concentration leads to the increase of the number of interactions,and vacancies will promote the crack growth of the alloys.The results of crack propagation law of Al0.1CoCrFeNi high entropy alloys with II-type crack are consistent with the existing physical experiment results.