Ta-10W with a high melting point of 3035 ℃, exhibits good mechanical properties at high temperatures, good thermal shock resistance, and a small coefficient of linear expansion. GH3128 is a single-phase high-temperature austenitic alloy with W and Mo as solid solution elements developed in China, resistant to corrosion and oxidation, with excellent creep durability and weldability. GH3128 is now being widely used in engine combustion chambers, air intakes, tail nozzles, radiators, and other components with density and cost lower than those of Ta-10W. In aero-engine manufacturing, the high-performance welding of Ta-10W with GH3128 not only significantly reduces the weight of the engine but also improves the engine thrust-to-weight ratio. In addition, engine manufacturing costs are significantly reduced while meeting the thermal service requirements of the engine at different locations. Welding Ta-10W with GH3128 combines the advantages of the two materials, allowing the exploration of useful methods for the manufacturing of key components in aero-engine high-temperature services.

The experimental material consisted of 25 mm×50 mm×3 mm GH3128 and Ta-10W plates. The welding light source was a fiber laser with a rated output power of 6000 W and a wavelength of 1060?1070 nm. A five-axis machine tool was used as the motion control system, and the positioning accuracy was 0.02 mm. The experimental diagram is shown in Fig. 1(a). Using the self-developed Ta-10W welding protection nozzle and high-purity argon (volume fraction of 99.999%) as the protective gas, the back protection device protects the back of the weld. The flow rate of the protection nozzle was 8 L/min, and the flow rate of the back was 8 L/min. Before welding, acetone was used to clean and ensure that the weld specimen had no wrong edges and no gaps in the interface. In the process experiments, initially, welding speed of 2 m/s, laser powers of 2500, 2750, and 3000 W, and defocusing amount of0 mm were used. The laser power was increased to 5000 , 5500 , and 6000 W, and the welding speed was increased to 5 m/min and 5.5 m/min. Finally, welding experiments with offsets of -0.2, 0.2, and 0.4 mm were performed under process parameters of 5500 W and 5 m/min. After welding, the front and back molding of the weld was observed using a super depth-of-field microscope. The sampling method is shown in Fig. 1(b). The welded specimens were cut into 10 mm×10 mm×3 mm block specimens using wire-cutting, and the metallographic specimens were prepared using the epoxy resin inlay method [Fig. 1(b)]. After sequential grinding and polishing with water-abrasive sandpaper, the welds were corroded using HCl and HNO₃ at a volume ratio of 3∶1 for 15?20 s. The cross-sectional morphologies of the welds and their microstructures were photographed using a super depth-of-field microscope. The microstructure of the weld was further observed using a scanning electron microscope and its accompanying energy dispersive spectroscopy (EDS) inspection equipment, to detect the physical phase of the weld. In the mechanical properties section, hardness tests were performed at 150 μm intervals using a Vickers hardness tester with a load of 200 g and a holding time of 15 s. The test area included the base material Ta-10W, GH3128, and the welds. In the tensile strength section, the room temperature mechanical properties of the joints were tested using a tensile testing machine. Considering the requirements of the testing equipment, small-sized tensile specimens were used for room temperature tensile tests [Fig. 1(d)].

Dissimilar materials Ta-10W/GH3128 have uneven weld structures. The Ta-10W side structure of the weld is dominated by short dendrites and equiaxial crystals, and the GH3128 side structure is dominated by needle-like columnar crystals. Under the processing conditions of focus center welding, an island-like structure appears in the weld, consisting of a Ta-10W reaction layer washed out into the molten pool and solidified. (Figs. 3 and 4). Under the process conditions of 5500 W, 5 m/min, and 0.2 mm, the weld tissue was relatively homogeneous; the island-like tissue disappeared; and the centerline of the weld was relatively clear (Fig. 5). A reaction layer was observed on the Ta-10W side in all three joints. For 5500 W, 5 m/min, 0.2 mm process conditions, the weld displayed an asymmetric X-morphology, and there were no cracks in the weld (Fig. 2). The thickness of the reaction layer was 5 μm near the Ta-10W side, whereas the thickness of the unmelted layer was about 2 μm near the GH3128 side. In the middle of the weld, both the reaction and unmelted layers disappeared (Fig. 4). The microhardness of the joint was lowest when welding offset was 343?416 HV (Fig. 9). The highest tensile strength of 428 MPa was observed for approximately 77.8% of the Ta-10W base material tensile strength (Fig. 10). The fracture mode of the joint was a mixed ductile-dominated fracture (Fig. 11).

The 3 mm thick Ta-10W/GH3128 with dissimilar butt joints was obtained in the atmospheric environment with a fiber laser. The weld exhibited an asymmetric X morphology at 5500 W, 5 m/min, and 0.2 mm processing conditions. The welded microstructures were relatively uniform consisting of mainly short dendrites, equiaxial crystals, and long columnar crystals. A reaction layer with a thickness of 5 μm was formed on the Ta-10W side and disappeared in the middle of the weld. The results of tensile experiments show that the sample broke on the Ta-10W side reaction layer. The tensile strength reached 428 MPa, and the joint displayed a mixed ductile-dominated fracture mode.