Adding Ta-based interlayer improve the performance of GH3128-Nb521 dissimilar material laser butt welded joints

Achieving high-performance dissimilar joint between Nb521 alloy and GH3128 alloy can expand the design space for structures operating in high-temperature environments. After direct laser welding, the Ni₃Nb–Ni₆Nb₇ eutectic are formed in the weld zone of the GH3128-Nb521 joint, causing immediate cracking after welding. In this study, a Ta interlayer was added and two-pass laser welding was performed on both the Nb521 side and the GH3128 side. The partially melted Ta interlayer isolated Ni and Nb elements, resulting in crack-free joints. A thin layer of Ni₃Ta intermetallic compound, approximately 8 μm wide, forms near the fusion line on the Ta side of the GH3128-Ta weld zone. This high-hardness layer causes the joint to fail along the fusion line on the Ta side during tensile test. The maximum room temperature tensile strength of the joint is approximately 145 MPa ± 42 MPa. Furthermore, a Cu/Ta composite interlayer is introduced. This approach significantly reduces the mixing of Ni and Ta, enabling effective joining of GH3128 and Nb521. Both the intermetallic compounds at the fusion line and in the fusion zone of GH3128-Cu/Ta are effectively suppressed. The tensile strength of the joint is increased to approximately 328 MPa, reaching about 60 % that of Nb521 base metal.