Dresden 2009 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 48: Nanostructured Materials IV
MM 48.3: Vortrag
Freitag, 27. März 2009, 10:45–11:00, IFW B
Annealing behaviour of equiatomic nanocrystalline NiTi alloy produced by high-pressure torsion — •Reeti Singh1, Sergiy Divinsky1, Ruslan Z. Valiev2, and Gerhard Wilde1 — 1Institut für Materialphysik, Westfälische Wihelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149, Münster, Germany — 2Institute of Physics of Advance Materials, Ufa State Aviation University,12 K. Marx Street, 450000 Ufa, Russian Federation
A nanocrystalline Ni50Ti50 alloy that had been severely deformed by high-pressure torsion (HPT) was investigated. Both amorphous and nanocrystalline phases were found to co-exist in the as-prepared state. Crystallization and structural changes during annealing were investigated by differential scanning calorimetry (DSC), X-ray diffraction analysis and transmission electron microscopy.
The DSC thermograms and X-ray analyses reveal stress relaxation and partial crystallization below 500 K while grain growth of the nanocrystals occurs predominantly after heating to temperatures above 523 K. The activation energy of grain growth was estimated to be 289 kJ/mole by applying a Kissinger analysis. Along with the amorphous phase crystallization, a continuous growth of pre-existing nanocrystals that are retained after HPT, is observed. The DSC signals observed during continuous heating experiments indicate an unusually large separation between the nucleation and the growth stages. This behavior, that also causes a large variation of the nanocrystal size after annealing at higher temperatures, is discussed with respect to the nanoscale microstructural heterogeneity after initial deformation.