Microstructures And Mechanical Properties Of Al_xCoCrFeNi(x=0.1?0.8) High-entropy Alloys Subjected To Thermo-mechanical Treatments

Multi-component high-entropy alloys(HEAs)have promising properties,such as high strength,hardness,and excellent oxidation resistance,attributing to the diversity of their chemical composition and microstructure.The single-phase face-centered cubic(FCC)HEAs exhibit ambitious tensile plasticity at room temperature,however,the strength is reltively low.In order to optimize the performance of HEAs,the microstructural defects including the additional atoms,dislocations,twins,grain boundaries,and precipitates are adjusted to improve the mechanical properties of HEAs.In this paper,the available thermo-mechanical treatments are ultilized to optimize the microstructures of Al_xCoCrFeNi(x=0.1?0.8)HEAs and the corresponding mechanical properties are studied as well,the following conclusions are drawn:(1)The addition of Al atom in Al_xCoCrFeNi HEAs can not only enhance the solid solution strengthening,but also introduce the new phase in present HEAs system.It is seen that when 0.1?x?0.45,the primary solidified phase is dentritic FCC structures.The experimental results indicate that the FCC and body-centered cubic(FCC+BCC)multiphase regions are at 0.45<x?0.8,and when 0.6?x,the as-cast alloys show a dual-phase(FCC+BCC)eutectic structure.(2)The cold rolling in Al_0.1CoCrFeNi HEAs with reductions of 50%and70%results in enhanced dislocation density,forming parallel-structured slip lines,shear bands,and deformation twins as well,and improves the strength of the alloys.Also,the transformation of Copper and Goss textures to Brass and Cu T textures is promoted by increasing the rolling reductions from 50%to 70%.The cold-rolled HEAs are subjected to anneal at 700??1000?for balancing the trade-off of strength and plasticity by obtaining partially and completely recrystallized single-phase microstructures.(3)Micro shear bands and high density dislocation cells are introduced in Al_0.25CoCrFeNi HEAs after cold rolling with various reductions from 0%to 90%,thereby increasing the tensile strength of the alloy from 526 MPa to 1479 MPa.Intercritical annealing(700??900?)in the cold-rolled HEAs can precipitate chemically segregated particles in present alloys,and the HEAs have good combination of strength and ductility at room and liquid temperatures.Single FCC phase HEAs are formed after annealing at 1100?,which exhibit significant size effect depending on the thickness of specimens.(4)Ultrafine and fine-grained dual-phase structures(FCC+B2)can be successfully obtained in the super-saturated Al_0.45CoCrFeN HEAs by adjusting the recrystallization and phase precipitation processes during annealing.Minor precipitates are further formed after aging in the inner of grains,which improves the mechanical properties.The dual-phase alloys dialpay much great microstructural stability during high temperature and long time annealing.(5)The eutectic Al_0.6CoCrFeNi and Al_0.8CoCrFeNi HEAs are subjected to cold rolling with reductions of 40%and 30%,respectively,to improve the hardness and strength.Subsequently,annealing the cold-rolled HEAs can optimize the mechanical properties.