Molecular Dynamics Study On The Strengthening And Toughening Mechanism Of Dual-phase High Entropy Alloys

High Entropy Alloys(HEAs)have opened up a new field of metal materials.HEAs use multiple main elements as the basic component,breaking the traditional design concept of single element-based alloys.Their structure and properties are different from traditional alloys in many aspects.HEAs have excellent mechanical properties,corrosion resistance,high temperature resistance,and other properties,making them one of the most promising new materials in the future.The crystal structures of HEAs are usually simple face centered cubic(FCC)structures,body centered cubic(BCC)structures,and closely packed hexagonal(HCP)structures.However,single-phase HEAs typically have a strength ductility trade-off effect.For example,single-phase FCC structure HEAs have excellent plastic deformation capabilities,but their relatively low strength will greatly limit the wide application of FCC structure HEAs.In order to obtain high strength and high plasticity HEAs,researchers have made a lot of efforts and achieved corresponding results.Research has found that introducing a second phase structure can break the strength ductility trade-off effect,in which both crystalline/amorphous dual-phase HEAs and FCC/HCP dual-phase HEAs can improve the strength of the material without losing its plasticity.Therefore,this paper systematically studied the effect of introducing amorphous phase into the crystalline phase on the mechanical properties and deformation mechanism of FCC structured HEAs,and clarified the interaction mechanism between dislocations and HCP structures in FCC/HCP dual-phase HEAs.This study provides a theoretical basis for the design and preparation of higher performance biphasic HEAs.The main research contents and conclusions of this article are as follows:(1)The introduction of amorphous phases into crystals can effectively improve the mechanical properties of crystal HEAs.In this paper,molecular dynamics simulations were conducted to investigate the effects of amorphous phase thickness,grain size,and element content on the deformation mechanism and mechanical properties of crystalline/amorphous dual-phase HEAs under uniaxial tension.The results show that due to the synergistic effect of crystalline and amorphous phases,the introduction of amorphous phases into HEAs crystals can improve the mechanical properties of HEAs.The results indicate that the yield stress and average flow stress of dual-phase HEAs are greater than those of single-phase polycrystalline HEAs due to the dependence of the stability of the crystalline/amorphous interface and the formation of shear bands on the size of the amorphous phase.As the thickness of the amorphous phase increases or the grain size decreases,the plastic deformation mechanism of HEAs gradually changes from dislocation slip in the crystalline phase to shear band movement dominated by the amorphous phase.It is found that changing the component content of the crystal phase can not only improve the strength of HEAs,but also improve their plasticity to a certain extent,thereby obtaining HEAs with high strength and good plasticity.(2)In recent years,the FCC/HCP dual-phase structure has been proposed as a new design strategy to achieve the high strength and plasticity of HEAs.In this paper,the effects of HCP phase thickness,strain rate,and temperature on the interaction mechanism between screw dislocations and HCP phase in FCC/HCP dual phase structure CoCrFeMnNiHEAs have been studied by molecular dynamics simulation.The results show that there are two interaction mechanisms between dislocations and HCP structures: one is that dislocations penetrate the HCP structure,which is the penetration mechanism,and the other is that dislocations are absorbed by the HCP phase,which is the absorption mechanism.The generation of these two mechanisms mainly depends on the relative ability of the HCP structure to prevent dislocation slip,which is closely related to the thickness,strain rate,and temperature of the HCP structure.When the relative ability of HCP structures to block dislocations is large,the interaction between dislocations and HCP structures exhibits an absorption mechanism;Otherwise,it presents a penetration mechanism.This research can provide theoretical guidance for the development and design of new high-performance HEAs to achieve high strength and high ductility of materials.