Microstructure and mechanical properties of electron beam welded Ta2.5W and GH3128 joints

Tantalum and nickel alloy components play a critical role in the aerospace sector, and their value can be maximized through efficient joining techniques. This study aims to elucidate the interface formation mechanism and fracture behavior of Ta/Ni weld joints via microstructural analysis. In this work, electron beam welding with different welding speeds was successfully employed to join 1 mm thick Ta2.5W and GH3128 plates. The mechanical properties of the welded joints were systematically investigated, and detailed microstructural characterization was conducted. Results indicate that Ta2.5W/GH3128 welded joints exhibit distinct brittle characteristics, with fractures consistently occurring at the reaction layer. Within the experimental scope, increasing welding speed led to enhanced tensile strength of the joints. Microhardness analysis revealed that the reaction layer in the weld constitutes a hard and brittle microstructure prone to crack initiation under stress. Fracture surfaces of the welded specimens displayed typical brittle fracture features, with uniform distribution of cellular (Ni₃Ta—Ni) eutectic structures. Electron backscatter diffraction was utilized for fine-scale microstructural characterization, identifying that the reaction layer primarily consists of dendritic tetragonal Ni₃Ta intermetallic compounds—hard and brittle phases that significantly degrade joint mechanical properties. Concomitant microstructural changes occurred in adjacent regions: GH3128 side grains underwent orientation reconstruction with Schmid factors approaching 0.5, while Ta2.5W side grains experienced lattice distortion and dislocation accumulation due to Ni₃Ta formation, resulting in increased hardness and embrittlement. This study reveals the brittle nature of tetragonal Ni₃Ta dendrites and eutectic structures within the reaction layer. It was found that increasing welding speed can reduce the thickness of the reaction layer and enhance joint strength, providing critical insights into the microstructure-property relationship for dissimilar welding of Ta/nickel-based alloys.