Numerical simulation and electron beam welding process optimization of Ta2.5 W alloy

Abstract

In this study, finite element analysis software Marc was used for numerical simulation of electron beam welding of Ta2.5 W and then welding tests were carried out. The temperature change and equivalent stress distribution were analyzed and discussed during the welding simulation. When conducting welding experiments, welding beam and welding speed were adjusted based on the morphology of welded joints. Afterwards, in order to investigate the microstructure, phase composition, texture, mechanical properties and the fracture mode of Ta2.5 W weld joints, related testing and characterization methods were carried out. The temperature field simulation results indicate that the peak temperature variation in the middle section of the weld is relatively stable, approximately maintaining at 4000 °C; the stress field simulation results indicate that there is an equivalent Von Mises stress of around 500 MPa in the center of the weld. Microstructural observation shows that increasing the welding beam and decreasing the welding speed properly could obtain a welded joint with good melt width on the front and back sides. According to EBSD, all the regions of welded specimen exhibit a {111} // Z fiber texture and the strength of texture is uneven, manifested as BM > FZ > HAZ. Mechanical performance testing shows that specimen 4 (welding voltage: 150KV, welding beam current: 5 mA, welding speed: 400 mm/min) performs the best in welded specimens, its ultimate tensile strength (UTS) and yield strength (YS) are 381 MPa and 353 MPa respectively, reaching 70 % of the strength of BM. However, the elongation is only 3.75 %. The fracture observation shows welded joint exhibits quasi-dissociative fracture, and nano-sized spherical particles (TaCx or Ta₂O₅) are found in the fracture. We speculate that its fracture occurs in FZ as a result of the combined effect of the presence of large residual stresses at the weld, the coursening of the center of the weld at the high-angle grain boundaries, and the inhomogeneous distribution of second-phase particles.