Microstructure Characterization in Dissimilar TIG Welds of Inconel Alloy 718 and High Strength Tensile Steel

Abstract

Nickel based super alloy Inconel 718 is widely used in aerospace and power generation industries. The dissimilar joining of high strength tensile steel to Inconel 718 was joined using TIG welding. The welding current and travel speed parameters were varied to identify the suitable welding conditions for achieving highest joint strength. Microstructural characterization of the weldments were evaluated by using optical, scanning electron microscope and energy dispersive spectroscopy analysis. The fracture surfaces of the tensile tested joints were investigated under scanning electron microscope to reveal the mode of fracture and its influence on the performance of the joints. Microhardness and tensile tests were conducted to evaluate mechanical properties of the joints. The microstructure evolution revealed that the formation of precipitates at the fusion boundary between the weld zone and Inconel 718 alloy. The hardness of the fusion boundary area id higher than the base metal and fusion zone on Inconel 718 side, whereas the highest hardness obtained in heat affected zone on high tensile strength steel. The strength of the joints were failed in the weld zone along the deposition of the filler metal, which strength is similar to the joint strength. The elemental line scan analysis confirmed the formation of Nb and Ti rich precipitates in weld zone and along the fusion boundary of Inconel alloy.