Role of boron additions on grain-boundary chemistry and tensile properties of Ni/sub 3/Al containing 24 and 26 at. % Al

Conference · Sun Jan 01 04:00:00 EST 1984

OSTI ID:6510913

Liu, C T; White, C L; Horton, J A

Effects of up to 0.4 wt % B in Ni/sub 3/Al containing 24 to 26 at. % Al were studied. Room-temperature ductility and fracture behavior of B-doped Ni/sub 3/Al depend critically on deviation from alloy stoichiometry. As the Al content of B-doped Ni/sub 3/Al is decreased below 25 at. %, the ductility increases dramatically and the fracture mode changes from intergranular to transgranular. Auger studies indicate that the intensity of boron segregated to grain boundaries increases and the concentration of grain-boundary Al decreases significantly with decreasing bulk Al concentration. These results suggest that alloy stoichiometry strongly influences grain-boundary chemistry, which, in turn, affects the grain-boundary cohesion. Boron exhibits an unusual segregation behavior in Ni/sub 3/Al, i.e., it has a strong tendency to segregate to the grain boundaries but not to cavity (free) surfaces. On the other hand, sulfur, an embrittling impurity, tends to segregate more strongly to free surfaces than to grain boundaries. The beneficial effect of boron is in agreement with existing theories of solute segregation effects on grain-boundary cohesion. The yield stress of B-doped Ni/sub 3/Al decreases with increasing grain size produced by long-term annealing at 1000/sup 0/C. The yield stress obeys the Hall-Petch relation: sigma/sub y/ = sigma/sub o,y/ + k/sub y/ d/sup -1/2/ with sigma/sub o,y/ = 163 MPa and k/sub y/ = 8.2 MPa cm/sup 1/2/. The tensile elongation was initially independent of grain size, and showed only a moderate decrease from about 50 to 40% with grain diameters larger than 110 ..mu..m.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6510913
• Report Number(s): CONF-8409142-1; ON: DE85001264
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102 -- Metals & Alloys-- Structure & Phase Studies
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
BORON ADDITIONS
BORON ALLOYS
CRYSTAL STRUCTURE
DOPED MATERIALS
DUCTILITY
ELONGATION
FRACTURE PROPERTIES
GRAIN BOUNDARIES
INTERMETALLIC COMPOUNDS
MATERIALS
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
NICKEL BASE ALLOYS
SEGREGATION
TENSILE PROPERTIES