Influence of a Ni-interlayer addition on microstructure, mechanical properties and corrosion resistance of dissimilar joints between Nimonic 75 alloy/Nitronic 50 steel using gas tungsten arc welding

The study investigates the effects of incorporating a nickel interlayer on the dissimilar metal weld (DMW) between Nimonic 75 superalloy (N75) and Nitronic 50 steel (N50) using the gas tungsten arc welding technique. A comparative investigation was made on the DMWs fabricated with and without an interlayer of 0.1 mm thickness. The weld metal (WM) fabricated with a nickel interlayer (named as interlayer weld) revealed the existence of both columnar and equiaxed dendrites compared to coarser columnar dendrites for the weld fabricated without an interlayer (named as autogenous weld). In addition, the interlayer weld facilitated the minimization of the welding thermal effects at the weld interface of the interlayer weld compared to the autogenous weld. The presence of finer equiaxed dendrites associated with a lesser degree of precipitation within the WM caused an increased microhardness, strength, and higher energy absorption for the interlayer weld. However, the fractured surfaces indicated ductile failure for both the DMWs. Additionally, the interlayer weld revealed improved corrosion resistance than the autogenous weld.