PNNL

Abstract

Intergranular oxidation of a Ni-4Al alloy exposed to hydrogenated, high-temperature water was characterized using directly correlated transmission electron microscopy and atom probe tomography. These combined analyses revealed that discrete, well-separated oxides (NiAl2O4) precipitated along grain boundaries in the metal. Aluminum was depleted from the grain boundary between oxides and also from one side of the boundary as a result of grain boundary migration. The discrete oxide morphology, disconnected from the continuous surface oxidation, suggests intergranular solid-state internal oxidation of Al. Keywords: oxidation; grain boundaries; nickel alloys; atom probe tomography; transmission electron microscopy (TEM)