Abstract
The current investigation focused on micro-plasma welding of superalloy 718 by constant current (CC) and pulse current (PC) mode. Formation of Nb enriched Laves intermetallic in the solidified weld fusion zone has detrimental impact on the weld mechanical properties. The influence of current pulsation on the weld microstructural morphology, formation of Laves phase, and its consequence on mechanical properties are meticulously studied herein. The tensile characteristics of the welded samples are observed to be inferior to the parent material due to formation of secondary Laves phase in the interdendritic region during solidification. PC mode weld have shown enhancement in hardness and tensile characteristics against the CC mode weld. The tensile ductility has shown significant improvement (47%) with the application of pulse current as compared to constant current mode of welding. Application of pulse current changes the mode of solidification in the fusion zone and enhance weld cooling rate, that leads to the refinement of fusion zone microstructure. The fusion zone refinement reduces the segregation of Nb in the interdendritic region and additionally curtails the magnitude of Laves phase formation.
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