Feasibility study of different filler metals on MIG-TIG double-sided arc brazing of titanium alloy-stainless steel

The feasibility of Cu, Cu-Si and Cu-Ni based filler metals on MIG-TIG double-sided arc brazing (DSAB) of TC4-304ss (Ti-SS) was studied. The microstructures and mechanical properties of the joints were investigated and compared. Defect-free Ti-SS brazing joints with double-sided sound forming were achieved using different filler metals. Thin reaction layers with the thickness of 75 mu m and 50 mu m were respectively formed at the Ti-side interfaces in the Cu filled joint and the Cu-Si filled joint, which mainly consisted of various Ti-Cu phases. The reaction layer with a width of 115 mu m formed in the Cu-Ni filled joint showed complex phases of beta-Ti, Ti2Cu, TiNi, Ti(Cu1-xNix)(2) (x = 0.20-0.82), (Cu1-x Ni-x)(1-y) Ti-y (x = 0-1; y = 0-0.14), TiCu4, Cu (s,s) phases. The Ti-Fe brittle phases formed at the SS side interface and weld zone in Cu-filled joint were replaced by the Ti-Si-containing phases in Cu-Si filled joint and Cu-Ni-containing phases in Cu-Ni filled joint. The tensile strength of the joints was 256 MPa, 273 MPa and 276 MPa, respectively. The Cu filled and Cu-Si filled joints fractured at the SS side interface due to the presence of the flat interface and the formation of brittle intermetallic compounds (IMCs). The Cu-Ni filled joint fractured at the thick Ti side interface, which induced by Ti(Cu1-xNix)(2) phase with high brittleness.