Microstructural characterization and mechanical properties of Ti3Al-Nb/Ni-based superalloy laser-welded joints with different type of V/Cu composite interlayers

Dissimilar welding of Ti3Al-Nb (Ti-24Al-17Nb) alloy and Ni-based superalloy with different type of V/Cu composite interlayers was performed by laser welding. Detailed microstructural characterization and mechanical properties of the laser-welded joints were investigated. The results indicated that laser welding can be achieved by using the three types of different V/Cu composite interlayers (Type I-0.2 mmV/0.2 mmCu, Type II-0.2 mmV/0.4 mmCu and Type III-0.2 mmV/0.6 mmCu). However, the type of V/Cu composite interlayers has a great influence on the composition distribution, microstructure and mechanical properties of the joints. When Type I was used, the dissimilar weld zone displayed mainly equiaxed and dendrite with fine grain size, and micro-crack was found in the weld. When Type II was used, the weld zone mixed of fine grain region (V-rich phase and Cu-rich phase) and coarse grain region (dendrite V-based solid solution and granular Cu-based solid solution in two-phase separation state). When Type III was used, the weld zone was mainly composed of large Cu solid solution, spherical Ni2V, Ni2V3 and unmelted V layer. The maximum room/high (873 K) temperature tensile strength of the joints was 312 MPa/240 MPa, which was obtained by using Type II. All the joints fractured at the interface on Ti3Al-Nb alloy side, indicating that the interface zone intermetallics were the main factor of affecting the mechanical properties of the joints. Moreover, the interface reaction layer between Ti3Al-Nb and unmetled V layer was also a weak link of Type III joint.