Comparative study on dissimilar welding of Inconel 718 and Udimet 500 precipitation strengthened nickel based superalloys

Abstract

Microstructural, mechanical and weldability aspects in the similar and dissimilar welds of alloy 718 and alloy 500 nickel based superalloys have been investigated. Alloy 500 weld metal showed high tendency of titanium to the segregation. Coalescence of the microvoids led to propagation of hot solidification microfissures. The alloy 718 weld metal displayed the formation of Nb rich low melting eutectic type morphologies, which can reduce the weldability. The microstructure of dissimilar weld metal with dilution of 65 wt-% displayed semideveloped dendritic boundaries. The less segregation and decrease in the low melting eutectics caused less susceptibility of dissimilar weld to solidification cracking. The segregation elimination phenomenon has occurred in the heat affected zone of alloy 500. In the partially melted zone, remelted and resolidified regions have been observed. These locations provided sites for nucleation of liquation cracks. For the alloy 718 heat affected zone, dissolution of γ″-Ni₃Nb needle-like precipitations has taken place. It was the chief reason for sharp decline of the microhardness. The heat affected zone of alloy 500 revealed intense liquation cracking, in which the crack is initiated at the partially melted zone. The hot liquation cracking in the heat affected zone of Alloy 718 was observed as a result of γ″-Ni₃Nb dissolution.

Keywords:

• Dissimilar welding
• Superalloy
• Weldability
• Microhardness
• Segregation
• Dissolution

Acknowledgement

The first author would like to thank the metallurgy team of Politecnico di Milano University, composed of Mrs S. Barella, Mr D. Mombelli and Mr A. Gruttadauria under supervision of Professor C. Mapelli, for their kind collaboration.