Microstructure and mechanical properties of dissimilar nickel-based superalloys resistance spot welds

Abstract

This paper addresses the factors affecting the mechanical properties of dissimilar resistance spot welds between Nimonic 263 and Hastelloy X nickel-based superalloys. The fusion zone (FZ) of the dissimilar weld displayed higher hardness values compared to the base metals which can be attributed to (i) the formation of Mo-rich carbide in the interdendritic zone due to positive segregation behavior of Mo and C during non-equilibrium solidification of the weld, (ii) the enhanced solid solution strengthening due to mixing of the base metals, and (iii) the formation of ultra-fine dendritic structure in the FZ due to ultra-fast cooling rate of the resistance spot welding. Formation of interdendritic carbides did not induce any brittleness in the FZ. The variation of weld heat input did not significantly influence the weld metallurgical attributes (e.g., chemical composition, dendrite arm spacing) and the hardness values of the FZ and heat affected zone. It is identified that controlling the weld physical attributes (i.e., fusion zone size and electrode indentation) is the key to achieve a dissimilar Nimonic 263/Hastelloy X resistance spot weld with adequate peak load and energy absorption and desirable failure mode (i.e., pullout mode).