Local electronic structure and cohesion of grain boundaries in Ni{sub 3}Al

Conference · Sat Jul 01 04:00:00 EDT 1995

OSTI ID:72470

Muller, D A; Subramanian, S; Sass, S L; Silcox, J ^[1]; Batson, P E ^[2]

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1. Cornell Univ., Ithaca, NY (United States)
2. IBM Thomas J. Watson Research Center, Yorktown Heights, NY (United States)

One of the fundamental questions concerning Ni{sub 3}Al is why doping with boron improves the room temperature ductility of the polycrystalline material. Boron is thought to prevent environmental embrittlement and increase the cohesive strength of grain boundaries since it changes the fracture mode from intergranular to transgranular. This change in cohesive energy must be reflected in the bonding changes at the grain boundary which can be probed using spatially resolved electron energy loss spectroscopy (EELS). The authors have examined grain boundaries in both undoped and boron doped Ni{sub 0.76}Al{sub 0.24} using EELS, EDX and ADF imaging in a UHV STEM.Ni-enrichment is seen in a 0.5--1 nm wide region at large angle grain boundaries, both in the absence and presence of B. EELS shows that B segregation can vary along the interface. The Ni L{sub 2,3} core edge fine structure which is sensitive to the filling of the Ni d-band, shows only the boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. These results demonstrate that boron segregation increases the cohesive energy and hence improves the fracture resistance of the grain boundary, by making the bonding at boundaries similar to that in the bulk. The measured changes in d band filling may also affect the local solubility of hydrogen.

• DOE Contract Number: FG02-85ER45211; FG02-87ER45322
• OSTI ID: 72470
• Report Number(s): CONF-941144--; ISBN 1-55899-265-0
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
BORON
BORON ADDITIONS
CHEMICAL BONDS
DUCTILITY
ELECTRONIC STRUCTURE
FRACTURE PROPERTIES
GRAIN BOUNDARIES
HEAT RESISTING ALLOYS
HYDROGEN EMBRITTLEMENT
INTERMETALLIC COMPOUNDS
MECHANICAL PROPERTIES
METALLURGICAL EFFECTS
NICKEL BASE ALLOYS