Functional bimetallic joints of Ti6Al4V to SS410

Abstract

Bimetallic structures provide a unique solution to achieve site-specific functionalities and enhanced-property capabilities in engineering systems but suffer from bonding compatibility issues. Materials such as titanium alloy (Ti6Al4 V) and stainless steel (SS410) have distinct attractive properties but are impossible to reliably weld together using traditional processes. To this end, a laser-based directed energy deposition (DED) system was used to fabricate bimetallic joint of Ti6Al4 V and SS410 keeping niobium (Nb) as a diffusion barrier layer. Both shear and compression tests were used to characterize the joint’s strength, and compared with the base materials. The bimetallic-joint shear and compressive yield strengths were 419 ± 3 MPa (∼114% of SS410) and 560 ± 4 MPa (∼169% of SS410), respectively. The increase in interfacial shear and compressive yield strengths over the base material indicates strong metallurgical bonding between the base materials and the interlayer, Nb. Proof-of-concept part for direct application of the bimetallic joint was demonstrated by welding base metals, end-to-end, to the joint. The interfacial microstructures, elemental diffusion and phases, including failure modes were examined using secondary and backscatter electron imaging, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The bimetallic-joint interfaces were free from brittle intermetallic compounds such as FeTi and Fe2Ti that are generally responsible for weak bond strength.