Annealing Effect On Microstructure And Mechanical Properties Of Deformed FeCoNi₂Mo_0.2V_0.5 High Entropy Alloy

High entropy alloys have been widely studied in the past twenty years.The high entropy alloy is composed of five or more elements,and the content of each element is between 5%and 35%.Due to its unique characteristics of"high entropy,cocktail,sluggish diffusion and lattice distortion effects,It has high strength,high wear resistance,high strength and great application potential in the fields of national defense and industry.Face centered cubic high entropy alloys have good plasticity but low strength.How to break the balance between strength and plasticity is always a research hotspot in the field of high entropy alloys.In this work,the effects of room temperature rolling and annealing on microstructure and tensile properties of FeCoNi₂Mo_0.2V_0.5 high entropy alloy was studied.At the same time,the annealing hardening phenomenon of 84.5%shape changing high entropy alloy was studied.The results are as follows:1.The original hot forged FeCoNi₂Mo_0.2V_0.5 high entropy alloy has a simple fcc structure and bimodal grain size distribution.A large number of dislocations are introduced during rolling deformation,and no phase transformation and twinning are induced.84.5%rolling deformation makes the hardness and tensile strength increased by 1.69 and 1.97times compared with the original hot forging state,respectively.2.Annealed at 600℃for 1 h for the 84.5%deformed FeCoNi₂Mo_0.2V_0.5 high entropy alloy results in annealing hardening,which results in a large number of orderly stacking faults and high density small angle grain boundaries recovered from dislocations.It is found that 84.5%of the deformed specimens have the characteristics of annealing hardening and slight deformation softening.Recrystallization occurs in 700℃,and ended at 900℃.With the recrystallization,the strength of FeCoNi₂Mo_0.2V_0.5 high entropy alloy decreases and the plasticity increases,which satisfies the Hall-Petch effect.3.By high temperature and short time annealing treatment,the mixed structure of partial recrystallization and deformation was obtained.Among them,850℃-15 min and850℃-20 min annealing processes obtained a good combination of strength and plasticity,The tensile strength and uniform elongation are 1131.4 MPa,12.7%and 1007.8 MPa,32.5%respectively.The excellent strength plasticity combination is mainly attributed to the large number of geometric dislocations and work hardening ability produced by the synergistic effect of soft phase and hard phase.