Fachbereich 11 - Physik
Institut für Materialphysik
Nanoanalysis of Interreactions

Stabilization of non-equilibrium B2 phase during reaction of Ni/Al

In the early stages of the reaction between Ni and Al, the formation of a metastable, Al-rich B2-phase had been reported as the first reaction product. We investigated the reaction mechanism by atomprobe tomography. A composition of 60 at% Al was proven by direct chemical analysis. Surprisingly, this early phase does only grow to a thickness of about 3 nm, although both reactive components are still present in abundance and no further competitive product appeared in the reaction zone. Based on Monte-Carlo simulations of the phase stability and the atomic transport, we proposed that this strange behaviour is related to the initial deviation from the equilibrium structure. At first an Al rich composition, weakly ordered, is formed to allow a fast transport and thus a fast release of free energy. During growth, the phase approaches its equilibrium, which results in a dramatic slowing down of the reaction rate.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft (SFB 345)

Beteiligte Wissenschaftler:

T. Jeske (Univ. Göttingen), G. Schmitz (Projektleiter)

Veröffentlichungen:

G. Schmitz, F. Hartung, T. Jeske, C. Lang and J. Schleiwies, Interreaction of metals - The dominant influence of microstructure, Advances in Solid State Physics, B. Kramer (ed.) 40, p. 543, 2000

T. Jeske, G. Schmitz, Nanoanalysis of the Early Interreaction Stages in Al/Ni, Scripta Mat. 45, 555, 2001

T. Al-Kassab, H. Wollenberger, G. Schmitz, R. Kirchheim, Tomography by Atom Probe Field Ion Microscopy, in F. Ernst, M. Rühle (eds.) High-Resolution Imaging and Spectrometry of Materials, Springer Verlag, Berlin 2003

T. Jeske, G. Schmitz, Influence of the microstructure on the interreaction of Ni/Al investigated by Tomographical Atom Probe, Mat. Sci. Eng. A327, 101, 2002

T. Jeske, G. Schmitz, Microstructural influence on the early stages of interreaction of Al/Ni- investigated by TAP and HREM, Mat. Sci. Eng. A (2003) in press

T. Jeske, Dissertation, Göttingen 2001