Near atomic scale studies of electronic structure at grain boundaries in Ni3Al

Why does boron doping improve the room temperature ductility of polycrystalline Ni3Al? Besides preventing environmental embrittlement, B changes the fracture mode from intergranular to transgranular, suggesting an increase in the cohesive strength of the grain boundaries. This change in bonding at the grain boundary has been measured using spatially resolved electron energy loss spectroscopy. The Ni L2,3 core edge, which is sensitive to the filling of the Ni d band, shows that only the B-rich regions of the grain boundary have a bonding similar to that of the bulk material. These changes suggest a simple model to describe the cohesion of the boundary. © 1995 The American Physical Society.