Metallurgical characterization and performance enhancement on Zr/Ti dissimilar laser welding with and without Nb interlayer

Due to the differences in thermophysical properties between Zr alloy and Ti alloy, defects such as cracks and pores appear in the welded joint , resulting in poor joint performance. To address this, laser welded joints of Zr alloy and Ti alloy were prepared using Nb interlayer with different thicknesses. The microstructure and mechanical properties of welded joints with and without interlayers were investigated. The results show that an appropriate interlayer thickness can enhance joint performance. When the thickness of the Nb interlayer is 1 mm, the joint exhibits optimum tensile properties of 311 MPa with a ductile fracture mode, which is different from the brittle fracture observed in the other three groups of samples. The Zr-Nb side has fine grain strengthening, which is the main reason for the improvement of the mechanical properties of the joint. With increasing thickness of the Nb interlayer, the microstructure in the WZ evolves progressively from α-Zr and α-Ti phases to a Nb-dominated structure. Nevertheless, an over-thick Nb interlayer impedes the formation of reliable dissimilar joining at both Zr/Nb and Ti/Nb interfaces.