Mechanical properties and microstructural evolution of in-service Inconel 718 superalloy repaired by linear friction welding

The focus of this study was to evaluate the possibility of extending the service life of an InconelA (R) alloy 718 (IN 718) aero-engine turbine using the linear friction welding (LFW) process. In particular, the repair of a blade integrated disk (BLISK) through replacement of blades damaged in-service was emulated by LFW virgin IN 718 to in-service IN 718. The virgin-in-service (V-IS) welds were then characterized to evaluate the evolution in the microstructural features, such as the grain size, delta phase, MC-type carbides and MN-type nitrides, across the weld region. In the as-welded condition, the weld and thermomechanically affected zones exhibited highly integral characteristics (i.e., no oxides, voids, or contamination), as well as no constitutional liquation of secondary phases (e.g., carbides and Laves phases). In the weld zone, grain refinement of the austenite (gamma) matrix was observed, using electron back scattered diffraction (EBSD), and related to the occurrence of dynamic recrystallization during LFW. The microhardness and tensile mechanical properties of the weldments were investigated in the as-welded condition and compared to weldments with a standard post-weld heat treatment (PWHT). The results suggest that the LFW process is a promising technology for refurbishing IN 718 aero-engine components.