Effects Of High Pressure Torsion On Microstructure And Properties Of High Entropy Alloys

High entropy alloy as a new alloy system breaks through design concept that the traditional alloy makes an element as the matrix.Because of the high entropy and lattice distortion and the difficulty of atom diffusion of high entropy alloy alloy,it is easy to obtain solid solution phase and nanostructure with high thermal stability,which makes high entropy alloy has high strength,high hardness and high temperature resistance.Meanwhile,the high entropy alloy has been used in the fields of grinding tools,tool preparation and turbine blades.High pressure torsion is the most effective method of severe plastic deformation.It can generate submicron or nanocrystalline under the combined actions of hydrostatic pressure,torsion force and friction force,so as to improve the mechanical properties of materials.In this paper,Fe4Mn4CoCr,Al0.3CrFe1.5MnNi0.5 and AlCrFe2Ni2 alloys are processed by high pressure torsion which is one of the severe plastic deformation processes,and their strengthening mechanisms are studied.The results of the research are as follows:The as-cast Fe4Mn4CoCr alloy is a solid solution to the fcc structure,the micro structure is dentrite and the hardness of as-cast alloy is 122HV.it gradually becomes the HCP(hexagonal close-packed)phase by high pressure torsion,In the process of torsion,the structure gradually changes from FCC to HCP phase,and the grain is refined to obtain nanocrystalline grain,and the grain size is between 10-80nm.The alloy microstructure is more uniform with the increase of strain.The hardness promote with the increase of equal effect,and increases to 526HV,which is 4.3 times as high as that as-cast alloy.The strengthening effect of the alloy is obvious under the mechanisms of phase transition strengthening and fine grain strengthening.The as-cast AlCrFe2Ni2 alloy is a two phase solid solution that the BCC(body centered cubic)and FCC(face centered cubic)hybrid structure coexist.After high pressure torsion,The BCC phase gradually transforms into the FCC phase.The grain gradually refines and the micro structure homogenizes gradually.After high pressure torsion,the hardness of AlCrFe2Ni2 alloy is raised from 366HV to 543 HV.The as-cast Al0.3CrFe1.5MnNi0.5 high entropy alloy is composed of B2(ordered body centered cubic)and BCC(disordered body centered cubic)structure solid solution.The hardness of as-cast Al0.3CrFe1.5MnNi0.5 alloy is 360HV.A part of the BCC structure transformed into sigma phase after high pressure torsion,When turning to the 1/4 circle,the hardness of the sample reaches 517HV,which is increased by 157HV compared with the as-cast state,indicating that high pressure torsion has strengthened the alloy.The strengthening mechanisms of the two alloys in the process of high pressure torsion mainly include phase transition strengthening and fine grain strengthening.The grain refinement,uniformity and mechanical properties of three alloys are improved with the increase of the circle in high torsion pressure.