Morphology Evolution of Grain Boundary Carbides Precipitated Near Triple Junctions in Highly Twinned Alloy 690

The evolution of carbides precipitated on grain boundaries near triple junctions in Inconel Alloy 690 following aging treatments at 715 °C for 2, 15 and 50 h were investigated by SEM and EBSD. The results show that, aging time does not influence the morphology of the carbides precipitated at grain boundaries, however, it does influence the morphology of carbides precipitated at triple junctions. Tiny carbides are precipitated at coherent Σ3 grain boundary, bar like carbides are precipitated at both sides of incoherent Σ3 grain boundary, while on only one side of Σ9 grain boundary, and the morphology of carbides precipitated on Σ27 and random grain boundaries are similar. Therefore, the type of nearby grain boundaries can influence the morphology of carbides precipitated at the other grain boundaries.