Structure, chemistry and bonding at grain boundaries in Ni{sub 3}Al. 1: The role of boron in ductilizing grain boundaries
Journal Article
·
· Acta Materialia
- Cornell Univ., Ithaca, NY (United States)
- IBM Thomas J Watson Research Center, Yorktown Heights, NY (United States)
Boron segregation is known to change the fracture mode from intergranular to transgranular in Ni-rich Ni{sub 3}Al. This paper addresses the question of why boron segregation at grain boundaries improves their resistance to fracture. Grain boundaries in B-free and B-doped Ni-rich Ni{sub 3}Al (76 at.% Ni) were examined using spatially resolved electron energy loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDS) and annular dark field (ADF) imaging in an UHV scanning transmission electron microscope, as well as conventional electron microscopy techniques. Ni-enrichment was seen in a 0.5--1.0 nm wide region at large angle boundaries, both in the absence and presence of B. using EELS, B segregation to the boundary was observed to vary along the interface. EELS of the Ni L{sub 2.3} edge showed that the B-rich regions have a bonding similar to that in bulk Ni{sub 3}Al, while the B-free regions have a bonding similar to the more Ni-like character of undoped boundaries. These results demonstrate that boron segregation increases the cohesive strength of grain boundaries in Ni{sub 3}Al by making the bonding at the boundary similar to that in the bulk and, in this manner, increases their fracture resistance.
- DOE Contract Number:
- FG02-85ER45211; FG02-87ER45322
- OSTI ID:
- 230801
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 4 Vol. 44; ISSN XZ504Y; ISSN 1359-6454
- Country of Publication:
- United States
- Language:
- English
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