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MM: Fachverband Metall- und Materialphysik

MM 28: Topical Session Theory meets Experiment I - Intermetallics and Steels

MM 28.2: Talk

Wednesday, March 28, 2012, 10:45–11:00, TC 006

Decomposition of cementite under strain in pearlitic steels: An ab intio study — •Gholamali Nematollahi, Johann von Pezold, Jörg Neugebauer, and Dierk Raabe — Max-Planck Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany

Severely plastically deformed pearlitic wires are amongst the strongest materials known to mankind. Despite extensive research the fundamental mechanisms underlying the extraordinary strength of this α-Fe/Fe3C composite are still unclear. Experimental evidence suggests that the applied strain induces a substantial migration of C atoms from cementite lamellae into adjacent ferrite particles, resulting in a dramatically increased C concentration in the ferrite matrix after the plastic deformation (by ~ 9 orders of magnitude). We therefore consider here the stability of C interstitials in ferrite and of C vacancies in cementite as a function of the relevant strain state, using density functional theory. Our analysis reveals a substantial strain-induced stabilization of the C interstitial in ferrite and a minor destabilization of the C vacancy in cementite. Using this insight we are able to explain the experimentally observed partial dissolution of cementite in severely plastically deformed pearlitic wires by the strain-induced stabilization of C interstitials in ferrite.

Keywords: Density functional theory, Ferrite, Cementite, Carbon interstitial, vacancy formation energy