Architecture Design,Microstructure And Mechanical Properties Of Doping Strengthened Non-equiatomic FeCoNiCr Based High-entropy Alloys

High entropy alloys(HEAs)is considered to be one of the important breakthroughs in alloying theory in recent decades.Their unique alloy design concept and significant high mixing entropy effect realize the controllability of properties,and has become the frontier hotspot of global research.How to further coordinate and balance the contradiction between strong and plasticity through component collocation is a scientific problem widely concerned by scholars at home and abroad.In this paper,Fe Co Cr Ni HEAs are taken as the research object,the phase composition and microstructure of the HEAs are adjusting by Mn element or Mn/Al elements in order to realize the purpose of strengthening and toughening.Taking TC4 titanium alloy layer as the strengthening layer,combined with Fe Co Cr Ni HEAs to build multi-layer heterostructure,play the role of mutual reinforcement,and realize the design and development of bionic laminated structure.(Fe Co Ni Cr)_100-xMn_x(x=0,12,20)HEAs were prepared by hot pressing.Fe Co Ni Cr HEAs were composed of FCC phases,(Fe Co Ni Cr)₈₈Mn₁₂ and(Fe Co Ni Cr)₈₀Mn₂₀ HEAs were composed of FCC+BCC dual phases,and second phase was precipitated at grain boundaries or in crystal.After annealing at 650?for 1 h,a large number of annealing twins were formed in(Fe Co Ni Cr)₈₈Mn₁₂ HEAs,and the texture of BCC phase was obvious.The Vickers hardness,bending strength and fracture toughness of HEAs increased first and then decreased with the increase of Mn content.Fe Co Ni Cr HEAs had good plasticity but low strength.(Fe Co Ni Cr)₈₈Mn₁₂ HEAs had the best comprehensive mechanical properties.After annealing at 650?for 1 h,the mechanical properties were further improved.The compressive yield strength was 874 MPa,the ultimate compressive strength was 1814 MPa,the fracture strain was 41%,the bending strength was 1574 MPa and the fracture toughness was 49 MPa·m^1/2.Al_x(Fe Co Ni Cr)_88-xMn₁₂(x=0,4,12,24)HEAs formed FCC+BCC dual phase structure after vacuum hot-pressing sintering at 900?,and the BCC phase increased with the increase of Al content.The content of BCC phase decreased after annealing.Al₄(Fe Co Ni Cr)₈₄Mn₁₂HEAs had the best comprehensive mechanical properties,with compressive yield strength of573 MPa,ultimate compressive strength of 1759 MPa and fracture strain of 40%.Its excellent mechanical properties were attributed to the strengthening effect of the second phase and hall Petch effect,as well as the regulation effect of small and medium angle grain boundaries of BCC phases.After annealing at 650?for 1 h,the texture of Al₄(Fe Co Ni Cr)₈₄Mn₁₂ HEAs was further optimized,the annealing twin structure appeared,and the mechanical properties were improved.The compressive yield strength was 741 MPa,the ultimate compressive strength was1833 MPa,the fracture strain was 39%,the bending strength was 906 MPa,and the fracture toughness was 21 MPa·m^1/2.The laminated configuration Fe Co Ni Cr HEAs was mainly composed of?-Ti,?-Ti and FCC phases after vacuum hot-pressing sintering at 900?,laminated configuration(Fe Co Ni Cr)₈₈Mn₁₂ HEAs was mainly composed of?-Ti,?-Ti,FCC and BCC phases.The laminated configuration Fe Co Ni Cr HEAs had the best comprehensive mechanical properties when the number of TC4 layers was 7,perpendicular to the direction of laminated structure,the yield strength,ultimate compressive strength,bending strength and fracture toughness were 654MPa,1335 MPa,773 MPa and 41 MPa·m^1/2 respectively,and the fracture strain was 11%.Parallel to the direction of laminated structure,the yield strength and ultimate compressive strength were 730 MPa and 917 MPa respectively,and the fracture strain was 3%.Good interface bonding effect and laminated configuration realized effective energy dissipation,which played an important role in improving the mechanical properties.