Interfacial characterization of diffusion bonded AISI 304L austenitic stainless steel and Inconel 718 with copper interlayer

Joining of Austenitic Stainless Steel (AISI 304L) and Inconel (IN718) with Copper (Cu) interlayer was carried out using diffusion bonding. The bonding process was performed at bonding temperature of 950 °C for 90 min of holding time under 5 MPa of bonding pressure. The resultant bonding interface was investigated for its microstructural, compositional, and nanomechanical characteristics using optical and scanning electron microscopy (OM and SEM) with energy dispersive spectroscopy (EDS), and nanoindentation. The results reveal that the microstructure of AISI 304L was comprised of an equiaxed austenitic matrix with annealed twins while IN718 was comprised of annealed twins along with the formation of MC and M 23 C 6 carbides. Additionally, the maximum nanohardness occurred at the bonding interface (3.42 GPa) and AISI 304 BM (3.13 GPa) in the Cu/IN718 and Cu/AISI 304L respectively. Moreover, AISI 304 BM has highest elastic modulus (223 GPa) at the Cu/AISI 304 bonding interface while at the Cu interlayer (141 GPa) in the Cu/IN718 bonding interface. Lastly, average values of H/E r and h c /h m reveals the pile-up behaviour around all the nanoindents.