Study On Preparation And Mechanical Properties Of High Entropy Alloy With Harmonic Structure

As a typical high entropy alloy,CrMnFeCoNi has been widely concerned by many scholars because of its excellent properties and simple microstructure,but its low strength at room temperature limits its application.In this basis,CrMnFeCoNi high entropy alloy with harmonic structure were successfully prepared by means of mechanical milling and powder metallurgy in this thesis,mechanical properties were improved through the design of the microstructure,and the effect of the ultrafine grain three-dimensional network space structure on the mechanical properties and deformation failure mechanism of CrMnFeCoNi high entropy alloy was mainly studied,which provides theoretical guidance for the development of high entropy alloy with high strength and ductility.The specific conclusions are as follows:(1).High entropy alloy with different grain sizes and ultrafine grain content can be obtained by adjusting the mechanical milling process.With the increase of mechanical milling time,the grain size of material decreases while the ultrafine grain content increases.(2).Harmonic structure can improve the comprehensive mechanical properties of the material,but with the increase of the ultrafine grain content,due to the effect of grain refinement,the ductility will inevitably decline.In this paper,the grain parameters of the optimized harmonic structure of CrMnFeCoNi high entropy alloy were obtained.(3).During the uniaxial tensile process,high entropy alloy with harmonic structure has heterogeneous strain distribution due to heterogeneous grain distribution.The heterogeneous distribution of strain between the coarse-grained and ultrafine-grained area will result in the storage of geometrically necessary dislocations(GNDs)at the Core/Shell interface,which will lead to the localization of plastic strain and promote the initiation of cracks during plastic deformation in this area.Therefore,cracks are more likely to occur at the Core/Shell interface during uniaxial tensile process.(4).By comparing the mechanical properties of harmonic structure and other heterogeneous structure,it can be found that the three-dimensional network structure can provide additional hetero-deformation induced(HDI)strengthening,thereby improving the strain hardening ability and uniformity of plastic deformation during tensile process,and the localization of plastic strain at the initial stage of deformation is avoided,which further improves the mechanical properties of the material.