Characterization of radiation-induced lattice vacancies in intermetallic compounds by means of positron-lifetime studies

Journal Article · Mon Jul 01 04:00:00 EDT 1996 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.54.849· OSTI ID:285951

Wuerschum, R; Badura-Gergen, K; Kuemmerle, E A; Grupp, C; Schaefer, H ^[1]

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1. Universitaet Stuttgart, Institut fuer Theoretische und Angewandte Physik, Pfaffenwaldring 57, D-70569 Stuttgart (Germany)

In the present paper a characterization of atomic vacancies in intermetallic compounds is given by means of positron-lifetime measurements after electron irradiation and comparison with the states after preparation, after long-time annealing, or in high-temperature equilibrium. In TiAl, Ti{sub 3}Al, and Ni{sub 3}Al no structural vacancies (detection limit {ital C}{sub {ital V}}=10{sup {minus}6}) are observed at ambient temperature. This confirms that in these compounds slight deviations from stoichiometry are compensated by antisite atoms. In the Al-poor {ital B}2 alloys FeAl and NiAl, on the other hand, remnant vacancies exist due to the high thermal equilibrium vacancy concentrations and their slow diffusivities. The kinetics of vacancy elimination in FeAl and NiAl is discussed. A substantial temperature dependence of the positron lifetime in vacancies is detected in close-packed intermetallics which is attributed to an increased atomic relaxation or partial positron detrapping at high temperatures. In contrast to that, the temperature dependence of the positron lifetime in vacancies is small in the open-structured {ital B}2 aluminides. The lifetimes {tau}{sub {ital f}} of free delocalized positrons in transition-metal aluminides and in NiZr and NiTi can be correlated to those of the pure components, taking into account the densities of valence electrons. For the positron lifetimes {tau}{sub 1} of vacancies in intermetallic compounds, values of {tau}{sub 1}/{tau}{sub {ital f}}=1.5{endash}1.7 are observed similar as in the pure metals. Annealing studies of {ital B}2-FeAl after electron irradiation yield time constants for the disappearance of vacancies identical to those deduced recently for the equilibration of thermal vacancies. In electron-irradiated Ti aluminides annealing processes at 250K and 450K are observed where the latter process is tentatively attributed to long-range migration of vacancies. {copyright} {ital 1996 The American Physical Society.}

• OSTI ID: 285951
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 2 Vol. 54; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM COMPOUNDS
ANNEALING
ELECTRON BEAMS
INTERMETALLIC COMPOUNDS
IRON COMPOUNDS
NICKEL COMPOUNDS
PHYSICAL RADIATION EFFECTS
POSITRON COLLISIONS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 273-400 K
TEMPERATURE RANGE 400-1000 K
TEMPERATURE RANGE 65-273 K
TITANIUM COMPOUNDS
VACANCIES
ZIRCONIUM COMPOUNDS