Effects of electron-beam offsetting on microstructure and mechanical properties of joints between titanium alloy and stainless steel using Cu/Nb bilayer

Abstract

Cu/Nb bilayer was utilized to join Ti-6Al-4V titanium alloy and AISI 316L stainless steel by electron-beam welding. Effects of electron-beam offsetting on microstructure and mechanical properties were studied. Microstructural characterization was carried out through optical microscopy, scanning electron microscopy with energy dispersive spectroscopy and x-ray diffraction. Results showed that dual-pass welding is better to achieve higher-quality joints than single-pass welding. When adopting dual-pass welding, the closer distance of first pass beam was to Nb layer side, the less contents of Fe and Cr were in the weld zone, and the phases changed from NbFe + NbFe2 + Cr1−xFex + NbCr2 + Cu based solid solution, NbFe + Cu3Ti + Cu based solid solution + Nb based solid solution to NbFe + Cu based solid solution + Nb based solid solution in weld zone. Owing to the formation of Cu-Fe and Nb-Ti solid solutions, the hardness of the weld zone was increased within 400 HV. Maximum average tensile strength of welded joints was 148.8 MPa, and fracture morphology changed from brittle mode to mixed fracture modes by adjusting first pass electron beam closer to the Nb side. Evolution of interfacial microstructure, formation and fracture mechanisms of the joints were summarized.