Quantitative Prediction of Solute Strengthening in Metal Alloys

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• Professor William Curtin, École polytechnique fédérale de Lausanne EPFL
• Friday 24 October 2014, 14:30-16:00
• Cambridge University Engineering Department, LR4.

If you have a question about this talk, please contact Ms Helen Gardner.

Please note that this is a Mechanics Colloquia

Alloys containing substitutional solutes exhibit strengthening due to favorable solute fluctuations within the alloy that hinder dislocation motion. Here, a quantitative, parameter free model to predict the flow stress as a function of temperature and strain rate of such alloys is presented.1,2 The model is related to early models and concepts but rectifies the many limitations of earlier works. The only inputs to the model are the solute/dislocation interaction energies in and around the dislocation core, which are computed using density functional theory within a flexible-boundary-condition method. The model then predicts the zero temperature flow stress and energy barrier for dislocation motion, and standard thermal activation theory then leads to the prediction of finite temperature/strain-rate flow stresses. The model is used to predict the flow stresses of various Al alloys and excellent results are obtained. The model is then used directly to predict basal strengthening in Mg-Al and Mg-Zn.3 Due to the different dislocation core structure, the model predicts a transition from flow controlled by short-range solutes to flow controlled by long-range solutes with increasing temperature and predictions agree well with experiments. The model is then applied to twinning in Mg, and yet new features emerge along with quantitatively accurate predictions. Finally, we discuss how the model is being extended to predict strengthening in new “high entropy” alloys, which are non-dilute, multi-component systems having fcc structure with random solute distributions (e.g. FeNiCoCrMn). Overall, this parameter-free model using first-principles input thus provides a basis for achieving the long-sought goal of computational design of alloys, within the context of solute-strengthening mechanisms. 1. G. P. Leyson, W. A. Curtin, L. G. Hector Jr., and C. Woodward, “Quantitative prediction of solute strengthening in aluminium alloys”, Nature Materials 9, 750-755 (2010). 2. G. Leyson, L. G. Hector, and W. A. Curtin, “Solute strengthening from first principles and application to aluminum alloys”, Acta Mater. 60, 3873-3884 (2012). 3. G. P. M. Leyson, L. G. Hector, and W. A. Curtin, “First-Principles prediction of yield stress for basal slip in Mg-Al alloys”, Acta Mater. 60, 5197-5203 (2012).

This talk is part of the Engineering - Mechanics and Materials Seminar Series series.

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