Grain boundaries in Ni 3Al—I. The local compositional order

Abstract

The local compositional order in the vicinity of grain boundaries in Ni 3Al, with and without boron, was examined using lattice imaging techniques. It was shown that small angle twist, tilt and mixed boundaries and large angle (near Σ = 5) twist boundaries were ordered up to very close to the interface plane. A compositionally disordered region ∼ 1.5 nm thick is present in the vicinity of a large angle general boundary in boron-doped Ni 3Al. Two large angle general boundaries are ordered up to very close to the interface in boron-free Ni 3Al. Image simulations were performed to identify possible imaging artifacts due to inclination of the boundary plane away from being edge-on. It was shown that the experimental observations of a locally disordered region cannot be explained as being an imaging artifact.