Influence of Cu interlayer on the interfacial strengthening of the diffusion-bonded SS-304L/IN718

Diffusion bonding (DB) of AISI 304L austenitic stainless steel (SS-304L) and Inconel 718 with and without Cu interlayer was performed at 950 degrees C for 90 min under vacuum of 8x10(-2) MPa. The resulting mechanical, microstructural, and compositional analyses of the bonded interfaces were analyzed using lap shear and microhardness tests, optical and scanning electron microscopes (OM and SEM) equipped with energy-dispersive spectroscope (EDS) and X-ray diffraction (XRD). It was observed that the bonding interface without Cu interlayer was comprised of TiC, NbC, Mn23C7, Cr23C6, Cr3C2, mu-phase (Fe2Nb), NiTi2, and FeTi. However, these carbides and intermetallic compounds (IMCs) were eliminated with the insertion of the Cu interlayer. This enhanced the joint strength from 143 to 334 MPa and reduced the interfacial hardness by 17 %.