Electrospark deposition Ni onto wedge-shaped Nb521 plates significantly enhances the performance of Nb521/GH3128 dissimilar material joints

Laser welding technology for Nb521/GH3128 dissimilar materials has significant application value in the aerospace field. In this study, a Ni-based surfacing weld layer (SWL) with different slopes was first deposited on a wedge-shaped Nb521 plate, which was then laser-welded to GH3128, resulting in high-quality Nb521/Ni- SWL/GH3128 dissimilar material joints. Test results indicate that the fusion zone (FZ) of the joints primarily consists of a (Ni)-based solid solution. The Ni-based SWL effectively prevents the formation of brittle NbNi phases. For joints with Ni-based SWL slopes of 1:3, 1:6, and 1:9, the average room-temperature tensile strengths were 378 ± 59.73 MPa, 446 ± 30.28 MPa, and 372 ± 38.71 MPa, respectively. All joints fractured at the Ni-based SWL/Nb521 interface, exhibiting brittle fracture characteristics. The Ni-based SWL consists of three layers: Intermetallic compound reaction layer, Nb-rich transition layer, and Ni-deposition layer. Its complex phase distribution and the significant hardness gradient, which induces stress concentration, make this interface the weakest area. In the joint with the Ni-based SWL slope of 1:6, high-temperature testing at 950 °C revealed a tensile strength of 209.6 MPa, with fracture occurring in the fusion zone (FZ). Electrospark deposition of Ni onto wedge-shaped Nb521 plates with an optimal slope of 1:6 significantly enhances the performance of Nb521/GH3128 dissimilar material joints. The room-temperature tensile strength reaches 90 % of the Nb521 base material's strength, and the high-temperature tensile strength at 950 °C reaches 94.8 % of that of the GH3128 base material at the same temperature.