Research On Vacuum Diffusion Bonding Of Zircaloy And 304L Stainless Steel With Ta/Ni And Nb/Ni Multiple Interlayer

Zirconium is known as"the first metal in the atomic energy era",which has excellent nuclear properties,corrosion resistance and high temperature mechanical properties.Zirconium and its alloys are commonly used as in-core materials in the nuclear industry.However,zirconium alloys are usually only used in the core components due to their high cost,and stainless steel with low radiation sensitivity,good weldability and machinability and low cost are usually used in non-core components.Therefore,it is necessary to connect the two materials in the application of nuclear power.It is of great significance to study how to achieve the reliable connection and make them give full play to their superior performance.In this paper,vacuum diffusion bonding technology was used to achieve reliable connection between SS 304L and Zr-4 alloy and SS 304L and Zr-2.5Nb alloy using Ni/Ta and Ni/Nb multiple interlayers respectively.SEM,EDS,XRD and other analytical testing methods were used to explore the effect of different bonding process parameters on the formation of joint interface microstructure,element distribution,interface evolution,fracture behavior,shear strength and microhardness.The interface structure of SS 304L/Ni/Ta/Zr-4 joint was composed of SS 304L/(Fe,Ni,Cr)/Ni/Ni₃Ta/Ta(Zr)+Zr(Ta)/Zr-4.The increase of bonding temperature made the grains of Zr-4 alloy became coarser,and transformed into lath-shape structure at 1000?.The thickness of each reaction layer increased with the increase of bonding temperature and holding time.The growth relationship of the Ni-Ta reaction layer conformed to the parabolic law.Its growth coefficient K value was 1.6215×10^-7m/s²,and the diffusion activation energy Q was 112.14kJ/mol.With the increase of bonding temperature and holding time,the shear strength of the joint showed a trend of first raised and then fell,and the highest shear strength was 194 MPa.The highest hardness value in the joint was 356 HV.The shear fracture position of the joint changed as the temperature raised.The the fracture mechanisms of the joint bonded at 900?-1000°C were brittle fracture.When the bonding temperature was 850?,the interface structure of SS 304L/Ni/Nb/Zr-2.5Nb joint was composed of SS 304L/(Fe,Ni,Cr)/Ni/(Ni,Nb)/?-Zr+Nb/Zr(Nb)/Zr-2.5Nb.When the bonding temperature was 900?,it was composed of SS 304L/(Fe,Ni,Cr)/Ni/Ni₃Nb/?-Zr+Nb/Zr(Nb)/Zr-2.5Nb.When the bonding temperature was 950?and 1000?,SS 304L/(Fe,Ni,Cr)/Ni/Ni₃Nb/?-Zr+Nb/Zr(Nb)/?-Zr+Zr(Nb)/Zr-2.5Nb was formed.The hardness test showed that the highest hardness value in the joint was 496 HV.The highest shear strength was 84.04 MPa.When the bonding temperature was 850?,the fracture position of the joint was between SS 304L and Ni layer.When the bonding temperature increased,the fracture position of the joint shifted to the joint area of Ni layer and Nb layer.The shear fracture mechanisms of joints bonded at 950?and 1000?were mainly brittle fracture,which combined brittle fracture with ductile fracture.