Effect Of Severe Plastic Deformation On Microstructure And Mechanical Properties Of FeCoNiCrMn High-Entropy Alloy

Face-centered cubic high entropy alloys,which have some attractive mechanical properties such as high fracture toughness,excellent ductility and cryogenic temperature damage tolerance,have been regarded as potential candidates for new structural and functional applications especially using as cryogenic tools materials.However,the low room temperature strength of face-centered cubic high-entropy alloys limits their widespread use in engineering structures.Therefore,how to break through the balance of strength and plasticity in the face-center structure high-entropy alloy has become a research hotspot in the field of materials in recent years.Grain refinement is considered to be an effective means of strengthening metals,which not only strengthens the material but also does not significantly deteriorate the plasticity of the material.Refining high-entropy alloy grains by the plastic deformation technique has also been extensively studied,such as by equal channel extrusion,high pressure torsion,and low temperature rolling.However,subject to the size of the sample,the industrial production of the above means is limited.In this study,large-scale high-entropy alloy plates with gradient and ultra-fine grain structure were prepared by asynchronous rolling and cumulative rolling.In the present study,the ASR was employed to process bulk Cantor alloy at room temperature.The microstructure and mechanical properties of the proceed materials were investigated.The traditional symmetrical rolling(SR)was also carried in the same processing environment.The microstructure and mechanical properties of the high-entropy alloy after accumulative rolling at different temperatures were also studied by accumulating the stacking at high temperature,room temperature and liquid nitrogen temperature.The high-entropy alloy was characterized by X-ray diffractometry,scanning electron microscopy and transmission electron microscopy.The mechanical properties of the high-entropy alloy were analyzed by tensile test and microhardness test.The experimental conclusions are as following:(1)Annealing after asynchronous rolling,a microstructure having a gradient structure can be obtained in a FeCoNiCrMn high-entropy alloy.(2)The gradient structure can obtain an excellent combination of high strength and good ductility,effectively improving the mechanical properties of the high-entropy alloy.The main reason compared to ordinary rolling is that the annealed rolled plate has an obvious back stress effect and the increased grain boundary strongly constrains the motion of geometric dislocations and promotes the spatial nucleation of new geometric dislocations.Therefore,asynchronous rolling can effectively improve the mechanical properties of the alloy.(3)By accumulating stack rolling,the limit of the existing equipment can be broken,and a larger deformation amount can be obtained,and an ultra-thin plate material can be obtained in the FeCoNiCrMn high-entropy alloy to obtain an ultra-fine grain structure.(4)Cumulative lamination at liquid nitrogen temperature can obtain a sheet of high strength and good plasticity.The main reason is that the cumulative rolling at liquid nitrogen temperature is more favorable for the formation of twins,the intersecting twins introduce more large-angle grain boundaries and the fineness of the grains is higher,which strongly hinders the slip of dislocations,thus making the material The strength is significantly improved.Therefore,the cumulative rolling at the liquid nitrogen temperature can effectively refine the grains and improve the mechanical properties of the alloy.