Cracking in fusion zone and heat affected zone of electron beam welded Inconel-713LC gas turbine blades

Abstract

Electron beam welding (EBW) of shrouds in Inconel-713LC low pressure gas turbine blades was associated with cracking in fusion zone (FZ) and heat affected zone (HAZ) leading to a high scrap rate in manufacturing of gas turbine blades. In this study, in order to develop a detailed map of cracks and understand the root cause of cracking, a comprehensive microstructural and numerical analysis was performed. The elemental mapping in scanning electron microscope (SEM)-energy dispersive spectral analysis revealed segregation of alloying elements in the cracked area of FZ and HAZ. In other words, one of the cracking mechanisms in FZ and HAZ was found to be segregation induced liquation and subsequent cracking due to thermal and mechanical tensile stresses generated during EBW. Cracking in FZ also occurred because of low strength of the solidifying weld metal as well as solidification contraction. As well, γ′ dissolution and reprecipitation in HAZ leading to decreased ductility and generation of contraction stresses was another mechanism for cracking in HAZ. The numerical model was capable to predict the cracking location as well as cracking orientation with respect to the weld line.