Interfacial microstructure and mechanical properties in diffusion bonded Inconel 718 to austenitic stainless-steel joints

Diffusion bonding (DB) of Inconel (IN718) with Austenitic Stainless Steel (SS-304L) was conducted by varying the bonding temperatures and times at 5 MPa of pressure under vacuum. The optimized joint interface was evaluated for its mechanical, nanomechanical, microstructural, and compositional analyses using shear and Vickers hardness tests, optical and scanning electron microscopy (OM & SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and nanoindentation. The results showed that the optimized bonding parameters for achieving a stable joint interface were 950 °C for 90 min of holding time. It was observed that the joint interface was comprised of NbC, Cr₂₃C₇, Fe₂Nb, and δ-Ni₃Nb. The maximum nanohardness of 3.5 GPa occurred in the joint interface which was 10% and 35% higher as compared to the base metals (BM) of IN718 and SS-304L, respectively. Lastly, maximum joint strength of 143 MPa was achieved with a joint efficiency of 37%.