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 segr egated B at grain boundaries were observed occasionally in the B-doped spec imens, the amount of B at the intergranular fracture surface drastically in creased with time upon exposure to the ambient vacuum. After subsequent rem oval of B by depth profiling by in situ Ar+-bombardment (1 keV) at a rate o f similar to3.3 nm/min, B again segregated to the Surface within several ho urs, 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 oxid ation and to less B surface segregation. (C) 2001 Elsevier Science B.V. All rights reserved.