Unveiling the failure mechanism on creep response of a casting Ni-based superalloy in thin-wall thickness

Abstract

With the improvement of thermal efficiency and the lightweight tendency of engine blades, Ni-based superalloy is widely used owing to its excellent performance in high-temperature atmospheres. This work studied the effects of surface oxidation, internal environmental attack, and matrix damage on the failure mechanism in a thin-walled casting Ni-based superalloy at 980 °C/160 Mpa. At the edge of the fracture, the sample suffered a severe environmental attack, resulting in the oxidation-affected zone forms. However, the loss of effective bear area induced by surface damage could not be the main reason for the sample's failure. At the interior of the matrix, voids were preferably initiated at the interface of MC carbides. As the increase of creep deformation, dynamic recrystallization (DRX) occurred at the tip of the voids, which increased the transverse grain boundaries and promoted crack propagation. Moreover, the DRX provided a short penetration path for the nitrogen, causing internal nitridation with AlN and Ti(Ta)N to precipitate. EBSD analysis confirmed that nitrides induced significant dislocations to accumulate at the boundaries of nitrides/γ, accelerating the failure of the sample.