Investigation of grain-boundary structure-segregation relationship in an N18 nickel-based superalloy

Abstract

Atom probe tomography and transmission electron microscopy were associated in order to characterize both structurally and chemically different general grain boundaries in a boron-doped N18 nickel-based superalloy. Boron, molybdenum and chromium segregation to the grain boundaries was demonstrated. The distribution of segregated atoms is shown to be non-uniform, both perpendicular to and in the plane of the grain boundaries. The Gibbsian interfacial excess was measured as a function of the misorientation angle and of the degree of twist-tilt character of the grain boundaries, leading to better knowledge of the structure-segregation rate relationship. For boron interfacial excess higher than a critical value, a thin chemically disordered film forms on each side of the grain boundaries. This film could explain the boron-induced mechanical reinforcement of the grain boundaries.