Grain boundarues in Ni 3Al—II. The dislocation structure of small angle boundaries

Abstract

The dislocation structure of small angle tilt and twist boundaries in ordered Ni 3Al, with and without boron, was investigated using transmission electron microscopy. Dislocations with Burgers vectors that correspond to anti-phase boundary (APB)-coupled superpartials were found in small angle [001] twist boundaries in both boron-free and boron-doped Ni 3Al, and a small angle [011] tilt boundary in boron-doped Ni 3Al. The boundary structures are in agreement with theoretical models proposed by Marcinkowski and co-workers. The APB energy determined from the dissociation of the grain boundary dislocations was lower than values reported for isolated APBs in Ni 3Al. For small angle twist boundaries the presence of boron reduced the APB energy at the interface until it approached zero. This is consistent with the structure of these boundaries containing small regions of increased compositional disorder in the first atomic plane next to the interface.