Regensburg 2013 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 32: Topical Session: TEM-Symposium - Structure-Property / In-Situ I

MM 32.2: Vortrag

Mittwoch, 13. März 2013, 10:45–11:00, H25

Grain size reduction by heating in nanocrystalline FeAl - a mystery solved by TEM — Christoph Gammer, Clemens Mangler, •Hans-Peter Karnthaler, and Christian Rentenberger — Universität Wien, Physik Nanostrukturierter Materialien, Boltzmanngasse 5, 1090 Wien, Austria

Bulk nanocrystalline materials show improved mechanical properties as compared to their coarse grained counterparts. Due to the high density of grain boundaries a thermodynamic driving force for grain growth exists and therefore, the thermal stability of a nanograined structure is usually low. In contrast, we show that in the present case of intermetallic FeAl made nanocrystalline by severe plastic deformation, a reduction of the grain size is occurring by heating connected with an increase in hardness [1]. High pressure torsion deformation of B2 ordered FeAl leads to a nanocrystalline material with strongly reduced long-range order. The samples show nanosized grains (about 70nm) with a high defect density and highly irregular grain boundaries. In-situ and post mortem TEM of thermally treated samples reveal a recurrence of the B2 superstructure [2], the re-arrangement of dislocations and what is rather unexpected, a reduction in grain size by a factor of 2. It is proposed that the decrease of the grain size during heating is linked to the recurrence of the long-range order by the interaction of the dislocations with the growing ordered domains. Therefore, subgrain boundaries turn into grain boundaries at a temperature too low for grain growth. [1] C. Mangler et al. Acta Mater 58 (2010) 5631. [2] C. Gammer et al. Scripta Mater 65 (2011) 57.