Slow removal of vacancies inB2−Ni52Al48upon long-term low-temperature annealing
| Autor: | R. Henes, Wolfgang Sprengel, K. Blaurock, Hans-Eckhardt Schaefer, K. J. Reichle, X. Y. Zhang |
|---|---|
| Rok vydání: | 2003 |
| Předmět: | |
| Zdroj: | Physical Review B. 68 |
| ISSN: | 1095-3795 0163-1829 |
| Popis: | Due to the high concentration and low diffusivities of thermal vacancies in $B2\ensuremath{-}\mathrm{NiAl},$ these vacancies are thought to be only then fully removed when long-term annealing at low temperatures is employed [H.-E. Schaefer et al., Intermetallics 7, 277 (1999)]. In the present paper the annealing of vacancies in ${\mathrm{Ni}}_{52}{\mathrm{Al}}_{48}$ in the temperature range from 635 K to 685 K on a one-year time scale is specifically studied by positron annihilation spectroscopy. The positron lifetime ${\ensuremath{\tau}}_{V}=(179\ifmmode\pm\else\textpm\fi{}1)\mathrm{ps}$ in as-prepared ${\mathrm{Ni}}_{52}{\mathrm{Al}}_{48}$ demonstrates the presence of remnant single vacancies. The decrease of the concentration of these vacancies with annealing time demonstrates that they can be removed by low-temperature long-term annealing leading to vacancy clusters. From the annealing a vacancy migration enthalpy of ${H}_{V}^{M}=(2.0\ifmmode\pm\else\textpm\fi{}0.1)\mathrm{eV}$ has been determined for ${\mathrm{Ni}}_{52}{\mathrm{Al}}_{48}.$ The remnant single vacancies are detected to be located on the Ni sublattice of ordered NiAl. The present results are expected to be of interest as an exemplary case that removal of vacancies and therefore thermal equilibrium in complex solids may be achieved only after long times. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|