Effect of TIG Welding on Microstructure and Mechanical Properties of Inconel 718

The effect of welding on microstructure and mechanical properties of Inconel 718 was investigated. In this study, the specimens welded by TIG (Tungsten Inert Gas) welding were subjected to two kinds of post-weld heat treatment (PWHT): 954℃ solution treatment+aging and 1045℃ solution treatment+aging. In both the solution treatments, two kinds of intermetallic compounds were observed in the interdendritic region of the weld metal, where δ-phase (Ni3Nb) and Laves-phase ((Ni,Cr,Fe)2(Nb,Ti,Al)) were precipitated. The relationship between mechanical properties and microstructures was examined. The tensile strength, elongation and creep rupture time of the weld specimen treated at 954℃ were decreased by TIG welding due to the coalescence of voids formed around Laves particles in the weld metal. Compared with the base metal, the hardness was decreased in the weld metal while it increased in HAZ (Heat Affected Zone). The solution treatment at 1045℃ resulted in dissolution of much more detrimental phases than the solution treatment at 954℃. As a result, the ductility and creep strength of weld specimen treated at 1045℃ were better than those of specimen treated at 954℃.