Regensburg 2016 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 60: Microstructure and Phase Transformations III

MM 60.1: Vortrag

Donnerstag, 10. März 2016, 15:45–16:00, H39

Mechanically driven BCC to BCT phase transformation during wire drawing conditions of pearlitic steel: An ab initio guided model — •Gh. A. Nematollahi1, S. Djaziri1, Y. Li1, C. Kirchlechner1, B. Grabowski1, S. Goto1,2, D. Raabe1, G. Dehm1, and J. Neugebauer11Max-Planck Institut für Eisenforschung, D-40237 Düsseldorf, Germany — 2Department of Materials Science and Engineering, Faculty of Engineering and Resource Science, Akita University, Tegata Gakuencho, Akita 010-8502, Japan

Cold-drawn pearlitic steel wires revealing ultra-high tensile strengths of up to 7 GPa are the world*s strongest bulk materials. Experimental observations reveal that cementite gradually decomposes during wire drawing. The C atoms resulting from the cementite decomposition are mechanically alloyed into the ferrite phase and accommodated in trapping sites around defects, such as dislocations. Surprisingly, there is also a high oversaturation of the bulk ferrite phase and experiments indicate a transformation to a tetragonally distorted system.In this work, a new ab initio informed model has been developed to take into account the strain-induced interaction of C with the host matrix as characteristic for wire drawing conditions. Our model captures the effect of the applied strain * exerted by the wire drawing process * within a renormalized C formation energy obtained by density functional theory calculations. Applying the model we demonstrate that the experimentally observed tetragonal distortion is due to a mechanically driven phase transformation from the body-centered-cubic (bcc) to the body-centered tetragonal (bct).

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