Internal Nitridation of Ni-Based Superalloy IN617 During Aging at 950 °C

Abstract Aging experiments were performed on Ni-based superalloy IN617 at 950 °C in air (containing 78.8 wt.% N2) for three different durations (50 h, 500 h, and 3000 h). Internal nitridation was found. The layered distribution structures of oxides, nitrides, and carbides were investigated. The formation of oxides and nitrides and the evolution of carbides during aging were analyzed. Results showed that oxidation only occurred in the nearest-surface vicinity, forming an external Cr2O3 layer and an internal Al2O3 layer as well as a Cr-depleted zone. With increasing aging duration, the oxide layer became continuous, and the thickness of the Cr-depleted zone was increased. Nitridation occurred in the sub-surface vicinity below the oxide zones. As aging duration was increased, there were increases in both the thickness of nitride zone and the nitride type. Specifically, only TiN was formed after aging for 50 h. When the aging duration was increased to 500 h, TiN and AlN both precipitated. TiN, AlN, and Cr3.25Ni1.75N all precipitated for the aging duration of 3000 h. At the zones far away from the external surface, the carbides including Cr-rich M23C6 and Mo-rich M6C were coarsened and transformed to discontinuous large blocks from the continuous thin film of the as-received condition under the effect of high temperature.