Defect structures in cold worked and small grain pure and boron-doped Ni/sub 3/Al alloys

Journal Article · Sun Jan 01 04:00:00 EST 1989 · J. Mat. Res.; (United States)

OSTI ID:6154733

Usmar, S G; Lynn, K G

Positron lifetime spectroscopy was used to study the isochronal annealing of cold worked Ni/sub 3/Al samples. In pure Ni/sub 76/Al/sub 24/, Ni/sub 74/Al/sub 26/, and boron-doped Ni/sub 74/Al/sub 26/ three annealing stages were observed. Boron-doped Ni/sub 76/Al/sub 24/ showed only two annealing stages. Vacancy annealing (stage III) was identified in all cases to start at /similar to/250 /sup 0/C, somewhat higher than previously reported. The discrepancy is suggested to be due to carbon-vacancy interactions, because carbon (impurties) was observed to diffuse out of all samples at or above /similar to/350 /sup 0/C. The high-temperature annealing stage in boron-doped Ni/sub 74/Al/sub 24/ (which is ductile) starts at 700--750 /sup 0/C and is complete at 1000 /sup 0/C. This stage was attributed to migration of dislocations to various sinks. In pure Ni/sub 76/Al/sub 24/, Ni/sub 74/Al/sub 26/, and boron-doped Ni/sub 74/Al/sub 26/ (which are brittle) the intermediate and high-temperature annealing stages occur at /similar to/750--800 and 1000 /sup 0/C, respectively. These stages were attributed to the migration of dislocations (750--800 /sup 0/C) and recrystallization (/similar to/1000 /sup 0/C) with incomplete annealing of dislocations at 1000 /sup 0/C. This being the case, it is clear that dislocations interact with grain boundaries fare more strongly in brittle than in ductile Ni/sub 3/Al alloys. Thus, these data strongly suggest that the ductilization of Ni/sub 76/Al/sub 24/ by boron is largley due to a change in grain boundary structure which inhibits the pinning of dislocations at grain boundaries that occurs in pure Ni/sub 76/Al/sub 24/ (i.e., boron increase the susceptibility of grain boundaries to slip). Similar results for small-grain samples support this interpretation.

• Research Organization: Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973
• OSTI ID: 6154733
• Journal Information: J. Mat. Res.; (United States), Journal Name: J. Mat. Res.; (United States) Vol. 4:1; ISSN JMREE
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
656002 -- Condensed Matter Physics-- General Techniques in Condensed Matter-- (1987-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
ALUMINIUM ALLOYS
ANNEALING
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BORON ADDITIONS
BORON ALLOYS
COLD WORKING
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
DUCTILITY
ELEMENTARY PARTICLES
FABRICATION
FERMIONS
GRAIN BOUNDARIES
GRAIN SIZE
HEAT TREATMENTS
HIGH TEMPERATURE
IMPURITIES
LEPTONS
LIFETIME
LINE DEFECTS
MATERIALS WORKING
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
NICKEL BASE ALLOYS
POSITRONS
SIZE
STOICHIOMETRY
TENSILE PROPERTIES