Dresden 2011 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 34: Nanomaterials I
MM 34.4: Vortrag
Donnerstag, 17. März 2011, 11:45–12:00, IFW B
Grain boundary segregation of carbon and formation of nanocrystalline iron-carbon alloys by ball milling — •Yuzeng Chen, Andreas Herz, and Reiner Kirchheim — Institut für Materialphysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Deutschland
Based on a novel defactants (defect acting agents) concept (R. Kirchheim, IJMR (Z. Metallkde) 100 (2009) 483 and Acta Materialia 55 (2007) 5129 and 5139), a novel method of understanding and synthesizing NC material was proposed by introducing defactants into materials to enhance the formation ability of nanocrystalline (NC) structures. Iron-carbon system was chosen as a model system where carbon acts as the so-called defactant. NC iron-carbon alloys with different carbon concentrations (C0) were prepared by ball milling. Afterwards, the as-milled powder with relatively low carbon concentration was annealed at a certain temperature to achieve saturation of GBs by carbon. Mean grain sizes of the powders (D) were investigated by TEM and XRD. The results indicated that once the saturation of GBs is achieved, D will be strongly dependent on C0 and will follow a mass balance of carbon in a closed system, i.e. D=3Γgb Vm /(C0−Cg) with Cg the carbon concentration in grains, Γgb the grain boundary excess, and Vm the molar volume. Based on the experimental results, the formation of NC iron-carbon alloys was treated within the framework of the defactant concept.