Dresden 2014 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 34: Poster Session

MM 34.26: Poster

Tuesday, April 1, 2014, 18:00–20:00, P4

Grain Refinement in Ball-Milled Nanocrystalline Iron in Dependence of its Oxygen Content — •Marie Trynogga, Christine Borchers, and Reiner Kirchheim — Institut für Materialphysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen

Nanocrystalline iron-oxygen alloys with different oxygen contents were prepared by ball milling of iron and hematite (Fe₂O₃) powder for 50 hours . The composition was identified using synchrotron diffraction and atom probe tomography (APT). The samples consist mainly of α-iron, segregated oxygen and magnetite (Fe₃O₄). The microstructure was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and APT. We observe that the grain size decreases with increasing oxygen concentration. This is interpreted as a decrease of the grain boundary energy of iron. To examine thermal stability, differential scanning calorimetry (DSC) and synchrotron diffraction measurements were performed in-situ during heating, revealing the formation of magnetite and grain growth. The nanocrystalline structure persists at higher temperatures indicating the formation of a grain boundary phase consisting of magnetite. Above 570^∘C the magnetite partly transforms into wüstite (FeO). We relate our findings to the results of a previous work studying nanocrystalline iron-carbon alloys after 100 hours of ball milling [1].

[1] Y.Z. Chen, A. Herz, Y.J. Li, C. Borchers, P. Choi, D. Raabe, R. Kirchheim, Nanocrystalline Fe-C alloys produced by ball milling of iron and graphite, Acta Materialia 61:3172-3185, 2013.