Influence of Diffusion Bonding Pressure on Microstructural Features and Strength Performance of Dissimilar Ti6Al4V Alloy and AISI 304 Steel Joints using Copper Interlayer

The joining of Ti6Al4V (Ti64) alloy and AISI 304 austenitic stainless steel (ASS 304) carries significant importance in aero-engines for turbine blade applications. However, it is difficult to join using fusion welding. The fusion welding of Ti64 alloy and ASS 304 steel promotes the evolution of various Fe-Cr-Ti and Fe-Ti intermetallics in weld zone owing to limited solid solubility of Fe, Cr, Ti, and Ni with each other. The evolution of these intermetallics deteriorates the strength properties of joints. Hence for joining Ti6Al4 alloy and ASS 304 steel, vacuum diffusion bonding (VBD) method is employed with thin Copper (Cu) foil as an interlayer. DB pressure extends a significant influence on microstructural evolution and strength of joints. So, for the feasibility of joining Ti alloy and ASS, the effect of DB pressure on microstructure and strength of joints is investigated. Results showed that the dissimilar joints of Ti64 alloy and ASS 304 steel developed using the DB pressure of 14 MPa exhibited greater lap shear strength (LSS) and bonding strength (BS) of 180 MPa and 268 MPa respectively. It is mostly related to improved joining interface coalescence and the development of the ideal bonding width with the least amount of embrittlement consequences. An increase in DB pressure increases the width of diffusion region which favors the development of detrimental intermetallics of Ti-Fe and curtails the strength of dissimilar joints.