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M: Metallphysik
M 23: Intermetallische Phasen I
M 23.2: Fachvortrag
Wednesday, March 28, 2001, 15:30–15:45, S5.3
Migration of vacancies in B2-Ni52Al48 intermetallic compounds studied by positron spectroscopy after long-term annealing. — •X.Y. Zhang1,2, W. Sprengel2, K. Blaurock2, K.J. Reichle2, and H.-E. Schaefer2 — 1Institute of Physics, CAS, Peking, P.R. China — 2Institut für Theoretische und Angewandte Physik, Universität Stuttgart, 70550 Stuttgart, Germany
The study of vacancies in intermetallic compounds is of particular interest because of the growing attention being paid to the relationship between the vacancy concentration and the mechanical strength1,2.
The migration of vacancies in the B2-Ni52Al48 intermetallic
compound annealed at very low temperatures, from 635 to 685 K, for long
times has been studied by the measurements of the positron lifetime and
the coincident Doppler broadening of the positron-electron annihilation
photon line. Three components were determined from the positron lifetime
spectrum of B2-Ni52Al48 annealed at 660 and 685 K for 60 days.
From these data the free lifetime τf was determined for the
first-time for a B2-NiAl compound. A fairly long lifetime component
was attributed to the formation of vacancy clusters
due to the agglomeration of vacancies at low temperatures.
By the time dependence of the vacany agglomeration the migration enthalpy
of the thermal vacancies at low temperatures in B2-Ni52Al48 was
determined. A change of the chemical environment of these vacancy
clusters in the annealed Ni52Al48 was also observed.
The work was supported by AvH (X.Y. Zhang) and DFG (SCHA428/17-3).
1) R.W. Cahn, Nature, 397, 656, (1999).
2) H.-E. Schaefer et al., Phys. Stat. Sol. (a), 160, 531,
(1997).