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The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.
Ram et al. (Fri,) studied this question.