Microstructure And Properties Of Zr705 Alloy Vacuum Diffusion Bonding Joint

Zirconium(Zr)has a low thermal neutron absorption cross section,high strength and hardness,excellent corrosion resistance and ductility,which is widely used in the fields of nuclear energy industry,aerospace and biomedicine.It is an important strategic material,also known as"the first metal of the atomic age".In order to further increase the stability of the use of Zralloy and reduce the difficulties in processing and manufacturing,it is essential to connect Zralloy.Therefore,it is very important to study the microstructure and properties of Zralloy after joining and forming through welding technology,and diffusion bonding as a commonly used material connection method,suitable for welding Zrand its alloy.In this study,Zr705 alloy was used as the base material,Cu was added as interlayer,and vacuum diffusion bonding was carried out under different welding conditions.The effect of the thickness of Cu interlayer and bonding temperature on the microstructure and mechanical properties of the diffusion bonded joints were mainly studied,and discussed the mechanism of joint formation.In addition,the corrosion resistance of joints in acid solution was tested by immersion corrosion experiment,and the corrosion resistance of bonded joints obtained under different interlayer thickness and bonding temperature was studied.The results showed that:(1)After adding Cu foil as an interlayer,at the Cu foil thickness 30?m-bonding temperature 900,920?and Cu foil thickness 10?m-bonding temperature 880,900,920?,two tyeps of microstructures were formed near the interface and the base material,namely Widmanstatten and duplex structure,which may be caused by the diffusion of Cu atoms.When the temperature exceeds 920?and reached 940 or 960?,the???complete transformation temperature was finished,and the entire base material was Widmanstatten structure.(2)When Cu foil thickness was 30?m-bonding temperature 900,920?and Cu foil thickness was 10?m-bonding temperature 880,900?,a layer of intermetallic compound was formed at the joint,and the compound layer contains Zr₂Cu,Zr₁₄Cu₅₁,ZrCu,ZrCu₅ and Zr₃Cu₈ phase,and there may be Zr₇Cu₁₀ and Zr₈Cu₅ phases.In addition,when Cu with a thickness of 10?m was used as the interlayer at the same temperature(920?),no intermetallic compound formed,indicating that the thickness of the Cu foil had a certain effect on the interface chemical reaction.When the bonding temperature was increased to 940?and 960?,the joints with 30?m or 10?m thickness of Cu as the interlayer had no intermetallic compound layer.The reason may be that at this bonding temperature,the diffusion rate and distance of Cu atoms into the matrix Zrwere accelerated,and Cu atoms were dissolved in the matrix Zr,and finally a wider Zr-Cu solid solution zone was formed.(3)Under the thickness of 30?m Cu foil,the ultimate tensile strength gradually increases as the temperature increasing,the elongation first increases and then decreases,and the turning temperature was 940?;under the thickness of 10?m Cu foil,the ultimate tensile strength and elongation both increased with the temperature.The mechanical properties of the joint with intermetallic compound layer were not good,which should be caused by the brittle and hard phase of the intermetallic compound,while the mechanical properties of the joint without the intermetallic compound were significantly improved.When the temperature was 940?,the ultimate tensile strength and elongation of the joints were the highest under each thickness,and increased from576 MPa and 23%of 30?m to 580 MPa and 32%of 10?m(the original base material is585 MPa,44%).(4)The corrosion rate of Zralloy in acidic corrosive solution was less than 0.5%/h.From the corrosion microscopic morphology,the corrosion resistance was:base material after bonding>bonding interface without intermetallic compound layer>original material>bonding interface with intermetallic compound.From the perspective of corrosion rate and weightlessness percentage,the original material had the highest corrosion rate and weightlessness percentage,with a weightlessness percentage of 44%.As the bonding temperature increased,the smaller the corrosion rate,the lower the weightlessness percentage.