Ultra high vacuum scanning Auger/electron microscopy studies of oxidation and B surface segregation of in situ fractured B-doped Ni3Al alloys

This paper focuses on local probe Auger spectroscopy studies of segregation and oxidation of in situ fractured Ni3Al specimens, both with and without B-doping. Although immediately after in situ fracture small amounts of segregated B at grain boundaries were observed occasionally in the B-doped specimens, the amount of B at the intergranular fracture surface drastically increased with time upon exposure to the ambient vacuum. After subsequent removal of B by depth profiling by in situ Ar+-bombardment (1 keV) at a rate of ∼3.3 nm/min, B again segregated to the surface within several hours, accompanied by surface oxidation, under ultrahigh vacuum conditions at room temperature. Possible mechanisms of B surface segregation are related to the high binding energy between B and O and the fact that B lowers the surface energy of a Ni-enriched surface. Finally, prolonged exposure of the fracture surface to the electron beam is shown to lead to enhanced Ni oxidation and to less B surface segregation.