Investigation of microstructure and mechanical performance in IN738LC joint by vacuum electron beam welding

A study of microstructure evolution and mechanical performance of vacuum electron beam welded IN738LC joint was performed. The joint obtained a typical bowl-like weld profile. No macro-cracks occurred in the fusion zone (FZ). The results of EPMA showed that obvious elemental segregation formed in the FZ. Microstructure characterization of FZ exhibited the existence of secondary micro-constituents, comprised of the ordered γ′ phase, MC carbide, γ/γ′ and γ/MC eutectic. The solidification processing of the precipitations in the FZ was adequately expounded. In the heat affected zone (HAZ), the γ′ particles were dissolved partially. The distance to fusion line and the size of γ′ particles affect the extent of dissolution of γ′ particles. liquation cracking was also observed, mainly resulting from the constitutional liquation of γ′ precipitates. The micro-hardness of the joint from base metal (BM) to FZ increased gradually, related to the formation of more MC carbides in the FZ and high-density reprecipitated γ′ phase in the FZ and HAZ. All the joints fractured in the BM at room temperature (RM) and 900 °C. Fracture analysis indicated that the joint tested at RM failed with a quasi-cleavage fracture mode, and the tensile fracture at 900 °C showed a dominant ductile rupture.