A novel electron beam offset barrier welding process for crack defect suppression in NiTi shape memory alloy and Ti6Al4V alloy joint

Severe crack defects significantly limit the application of NiTi SMA/Ti6Al4V fusion welded joints in aerospace engineering. Currently, there is a lack of effective electron beam welding techniques to control the formation of such cracks. This study developed an electron beam offset barrier welding technology based on beam offset to eliminate crack defects. Results demonstrated that merely adjusting the electron beam offset distance toward the Ti6Al4V side could not suppress crack formation. The weld zone produced abundant brittle Ti₂Ni intermetallic compounds and extremely high transverse residual tensile stresses, leading to longitudinal cracks. Crack-free joints were achieved by introducing a Mo barrier layer and optimizing its thickness, height, and beam offset distance. The 300 μm thick Mo layer effectively prevented base metals mixing, substantially reducing Ti₂Ni formation. The diffusion layers, primarily formed through Mo-Ti interdiffusion, established robust joining between the Mo layer and both base materials. The joint strength increased from 76 MPa to 308 MPa, with the fracture location shifting from the Ti₂Ni reaction layer to the Mo barrier layer. This study provides a novel strategy for controlling crack defects in dissimilar material welded joints with poor metallurgical compatibility, and promotes the engineering application of NiTi shape memory alloy/Ti6Al4V alloy electron beam welded joints.