Regensburg 2013 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 51: Nanomaterials - Nanocrystalline & Porous Materials I
MM 51.3: Talk
Thursday, March 14, 2013, 10:45–11:00, H25
Stabilization of Nanocrystalline Iron by Segregation of Carbon at the Grain Boundaries — •Marie Christine Trynogga1, Andreas Herz2, Yuzeng Chen3, Christine Borchers1, and Reiner Kirchheim1 — 1Georg-August-Universität Göttingen, Institut für Materialphysik, Friedrich-Hund-Platz 1, 37077 Göttingen — 2TU Ilmenau, FG Werkstoffe und Elektrotechnik, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau — 3State Key Lab of Solidification Processing, Northwestern Polytechinical Univeristy, Xi’an, China
A nanocrystalline iron-carbon alloy was produced by high-energy ball milling to experimentally confirm the defactants (defect acting agents) concept, which was introduced in [1]. For this system the defactants concept predicts that the carbon atoms act as segregating solute atoms, i.e. the carbon is enriched at the grain boundaries and significantly reduces the grain boundary energy. So the formation of grain boundaries is favoured, stabilizing the grain boundaries leading to a nanocrystalline structure.
Iron powder was mixed with graphite reaching carbon concentrations of up to 4.3 wt.%. The samples were produced by high-energy ball milling. The microstructure was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was observed that the α-iron structure persists and the grain size decreases with increasing carbon concentration. This dependence follows from the defactants concept connected with a simple mass balance of carbon in a closed system.
[1] R. Kirchheim, Acta Materialia 55 (2007) 5129 and 5139