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MM: Fachverband Metall- und Materialphysik

MM 5: Materials Design I

MM 5.2: Vortrag

Montag, 23. März 2009, 10:30–10:45, IFW D

Effect of interstitial carbon on the magnetic structure of fcc iron: Towards an ab-initio understanding of austenitic steels — •Lars Ismer, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH,Max-Planck-Straße 1,40237 Düsseldorf,Germany

It is known that the mechanical properties of austenitic steels strongly depend on their carbon content. However, the impact of carbon on the stability of the complex magnetic structure of the austenitic iron host is still controversially debated in the literature. Therefore, we present a systematic ab initio investigation of the interaction of interstitial C with the magnetic structure of austenitic iron. Our results are obtained within the DFT-GGA approach, making use of the PAW method and the collinear approximation for the magnetic moments. We find a principle preference of the C atoms for a FM environment. However, this yields only for very high carbon concentrations (>10 at.%) to a preference of the FM structure for the entire austenitic crystal. For lower concentrations (< 3 at.%), the anti-ferromagnetic double layer (AFMD) structure, representing the magnetic ground-state of pure fcc-Fe, remains the most stable phase. The transition from AFMD to FM ordering takes place at 8 at %, is surprisingly sharp, and a collective phenomenon of all C atoms in the Fe host matrix.