Microstructure and Damage Evolution of Inconel 740H Welded Joint during Creep Process at 750 °C

In this present study, the microstructural and damage characterizations of Inconel 740H alloy welded joint during creep process at 750 °C and 210 MPa were investigated via scanning electron microscopy, electron back-scattered diffraction, and transmission electron microscopy. For the base metal (BM), no significant change for austenite grains occurs with increasing creep time from 1000 to 2651 h. Creep cavities mainly distributed along the grain boundaries are formed due to the existence of larger M 23 C 6 carbide. After the creep exposure for 2651 h, creep cracks are formed as a consequence of the coalescence of several creep cavities. In comparison to heat affected zone (HAZ), weld metal (WM) shows fewer creep cavities, which implies that WM exhibits superior creep property. No obvious textural features are present for Inconel 740H welded joint after creep at 750 °C for different regions. There is no significant coarsening for γ ′ precipitates in size, which implies that γ ′ precipitates show superior high-temperature stability. In comparison to BM and HAZ, WM shows higher dislocation density due to welding thermal cycling. The interaction behavior of dislocations and γ ′ precipitates was enhanced, which can significantly strengthen the γ matrix.