Revealing the fatigue crack propagation mechanism of a Ni-based superalloy electron beam welded joint through in-situ SEM observation

[Display omitted] •The fatigue crack growth mechanism of GH4169 EBW joint is revealed by in-situ SEM.•Welded joint shows a good static strength, but worse ductility than base material.•Pre-cracked welded joint has longer fatigue crack growth life than base material.•The FCGR curves of welded joint and base material intersected with each other. In this study, in-situ scanning electron microscope (SEM) fatigue crack propagation experiments for electron beam welded joints of GH4169 Ni-based superalloy are carried out. Based on material characterization and analysis, the corresponding fatigue crack propagation mechanism of the welded joint (WJ) is investigated. Compared to the base material (BM), the WJ has comparable static strength, but worse plasticity. Significantly, the WJ has longer fatigue crack growth life than that of the BM. The fatigue crack growth rate (FCGR) curves of the WJ and the BM intersected with each other. In particular, under low stress intensity factors (ΔK) level, the FCGR of the WJ is lower than that of the BM. Under high ΔK level, the FCGR of the WJ is higher than that of the BM. The steep FCGR curve of the WJ can be attributed to the unique weld texture and a shielding effect caused by the weld strength mismatch.