Effects of laser beam offsets on the microstructures and properties of Ta10W/Nb521 dissimilar joints

The reliable welding of Ta10W and Nb521 can improve the performance and design flexibility of key components of aerospace engine. However, due to the large differences in composition and physical properties, the welding will lead to uneven distribution of microstructure and mismatched joint properties, etc. This study explores the effects of laser beam offset (LBOs) on the microstructures and mechanical properties of Ta10W/Nb521 dissimilar joints. Results show that the fusion zone (FZ) dendrite regions are mainly (Nb)-based solid solutions, surrounded by (Ta)-rich areas, causing non-uniform composition distribution, which intensifies as the laser beam shifts from Nb521 to Ta10W. As LBO increases from −0.2 mm to +0.2 mm, the average FZ width and hardness rise, while the average grain size in the joints first decreases and then increases. The room-temperature tensile strengths of joints with LBOs of −0.2 mm, 0 mm, and +0.2 mm reach 93.9 %, 96.5 %, and 93.8 % of Nb521 base metal strength, respectively. All joints show brittle fracture. Those with LBOs of −0.2 mm and +0.2 mm fracture in the FZ, while the joint with LBO of 0 mm fractures at the Nb521/FZ interface. The LBO = 0 mm joint has the smallest grain size and uniform grain orientation distribution, hinder the dislocation slip and enabling more uniform deformation. Additionally, the H/E and H 3 /E 2 ratios of this joint are superior to those of the LBO = +0.2 mm joint and are similar to those of the LBO = −0.2 mm joint. Combined effects of these factors make the LBO = 0 mm joint show better plasticity.