Vacuum Diffusion Bonding And Interfacial Elements Diffusion Behavior Between Zirconium And Steel

Vacuum diffusion bonding is widely used in the field of dissimilar materials connection.Zirconium has excellent properties including low neutron absorption cross-section,high temperature corrosion resistance,easy fabricability and so on.Q345 steel belongs to low-alloy high-strength steel which also has good plasticity and welding performance.Zirconium and Q345 steel composite platels commonly used in chemical reaction vessel shell.However,it is difficult to bond zirconium and steel directly due to the great difference between the physical and chemical properties.The vacuum diffusion bonding technology using interlayer can solve this problem.In this paper,pure zirconium and Q345 steel were bonded with thinner Cu-based amorphous foil alloy as the interlayer at 700?based on previous studies.The thickness of the reaction layer was controlled under melting conditions.A series of analytical test methods including optical microscopy,SEM,EDS,XRD,EBSD,microhardness test,shear test and three point bending test were used.The purpose was to study the relationship between the microstructure and the mechanical properties.At the same time,it was also proposed pure aluminum foil as the interlayer material at a lower temperature??620??.The thickness of reaction layer was controlled by non-melting conditions.The purpose was to study the relationship between the microstructure and the mechanical properties,and the thermodynamics and kinetics of the growth of the reaction layer were also studied.A composite plate of pure zirconium and Q345 steel was fabricated by diffusion bonding with Cu-based interlayer at a low temperature of 700?and a low pressure of 3 MPa for 1h.Metallurgical bonding was successfully discovered at the interface,and the interfacial reaction phases were composed of multilayers.The interfacial reaction phases were divided into five regions,followed by Fe₃P,Cu,CuNiPZr,Cu₅₁Zr₁₄ and Cu₃Zr₂,where the Zr element occupies a wider area than the Fe element.The total thickness of the reaction layer in 30?m and 60?m thick interlayer was 27?m and 31?m,respectively.There were many holes and defects in the reaction layer,and the maximum shear strength and bending strength were 30MPa and 803MPa,47MPa and 1017MPa,respectively.When the thickness of the Cu-based interlayer was increased to 90?m,the total thickness of the reaction layer was 63?m and the number of holes reduced greatly.Two kinds of dendritic eutectic structures formed in the Cu.The interfacial bonding quality was greatly improved,and the maximum shear strength and bending strength were 88 MPa and 1079 MPa,respectively.The mechanism of shear fracture was studied.The results showed that as the thickness of Cu-based interlayer increases,the crack initiation in the reaction layer decreases,and the crack propagation path and dendritic eutectic resistance increases.Therefore,the maximum shear strength of joint with 90?m thickness Cu-based interlayer was obtained.The mechanism of front and back bending fracture were studied.The results showed that the pores in the reaction layer were closed under the compressive stress in the front bending test and open under the tensile stress in the back bending test.This was why front bending performance outperforms back bending.A composite plate of pure zirconium and Q345 steel was fabricated by diffusion bonding with Al foil at low temperature form 545?to 575?and a low pressure of 3 MPa form 3h to4 h.The interfacial reaction phases are mainly consisted of Al₅Fe₂ and Al₃Zr,and a layer of micron-level transitional phase Al₃Fe and toothed Al₃Zr₂,respectively.Increasing the diffusion temperature and prolonging the diffusion time could increase the total thickness of the reaction layer.The thickness of Al₅Fe₂ layer was wider than that of Al₃Zr.The morphology of transitional phase Al₃Fe and Al₃Zr₂ were clearer.However,prolonging the diffusion time would cause the transition phase to gradually dissolve into the matrix.The mechanical properties showed that Al₅Fe₂ had the highest microhardness and the shear crack completely expanded in Al₅Fe₂.When keeping the diffusion time at 3 h,the maximum shear strength of composite plate was measured to be 30 MPa at 575?,but the interface between Al₅Fe₂ and Al was broke at590?.When keeping the diffusion temperature at 560?,the maximum shearing strength of composite plate was measured as 37 MPa with 3.5 h.The EHF thermodynamic model caculation indicates that,Al₅Fe₂ and Al₃Zr have the most negative effective enthalpy of formation as the first generation phase.The kinetics equation of diffusion with temperature are x_Al5Fe2=1.01×10⁴exp?-126800/RT?and x_Al3Zr=1.57×10¹¹exp?-249400/RT?,respectively.The kinetic equation of product diffusion with time are x_Al5Fe2=5.37×10^-16t².81.81 and x_Al3Zr=1.93×10^-14t^2.3,respectively.Al₅Fe₂ shows a wave shape with a common[001]direction?c-axis?,while Al₃Zr has no obvious specific orientation.