Effect of texture evolution and defect on the crack initiation of a Ni‐based superalloy electron beam welded joint

Abstract

Electron beam welding (EBW), a high‐quality and precise joining process, is widely used in aerospace manufacturing. In this study, through in situ scanning electron microscope (SEM) fatigue experiments and X‐ray computed tomography (CT) scanning technology, we revealed the fatigue crack initiation and propagation mechanism in GH4169 superalloy EBW joints under different post‐welding heat treatment conditions. The welded pores have a decisive effect on the fatigue properties of direct aging treatment welded joints. Fatigue cracks initiate from pore defects on the surface or in the subsurface. Due to the heterogeneous microstructure in weld seam, fatigue cracks tend to grow along the primary dendrite axis and secondary dendrite arms. Besides, in homogenization and aging treatment specimen, intergranular fatigue cracks tend to nucleate in the slip zone of large grains and twin boundaries. Although homogenization treatment can eliminate segregation, it also results in significant grain growth in both weld seam and base material.