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A multiscale modelling strategy for virtual design of metallic alloys

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A MULTISCALE MODELING STRATEGY FOR VIRTUAL DESIGN OF METALLIC ALLOYS

Javier LLorca

IMDEA Materials Institute, c/ Eric Kandel 2, 28906 – Getafe, Madrid, Spain & Department of Materials Science, Polytechnic University of Madrid, 28040 – Madrid, Spain

A simulation roadmap is presented to carry out virtual design, virtual processing and virtual testing of metallic alloys for engineering applications. The strategy is based on a bottom-up, multiscale modelling approach which runs along two parallel lines: simulation of the microstructural development during processing (virtual processing) and simulation of the mechanical behavior form the microstructure (virtual testing). Modeling efforts begin with ab initio simulations and bridging of the length and time scales is accomplished through different strategies which encompass the whole range of length and time scales required by virtual design, virtual processing and virtual testing. Nevertheless, not everything can or should be computed and critical experiments are an integral part of the strategy for the calibration and validation of the multiscale strategies at different length scales.

Two examples of application of the different parts of the strategy for virtual processing and virtual testing are presented in detail. The first one deals with the prediction of size and morphology of the θ’ precipitates during high temperature aging of Al-4wt.% Cu alloys. The lattice parameters and elastic constants of θ’ precipitates and of the α-Al matrix were calculated using first principles density functional theory, whereas the interfacial energy between θ’ phase and α-Al matrix was determined by means of molecular dynamics. This information was used to analyze the equilibrium shape and the evolution of θ’ precipitates using the phase field method. The second one is focused on the prediction of the mechanical properties of two different polycrystalline alloys (AZ31 Mg alloy and IN718 Ni-based superalloy) by means of computational homogenization of a representative volume element of the microstructure which was built with the grain size, shape and orientation distributions of the material. The mechanical behavior of each grain was simulated by means of a crystal plasticity model which takes into the effect of twinning (in the case of Mg alloys) as well as evolution of the critical resolved shear stress with deformation in each slip system (including viscoplastic effects as well self and latent hardening). The parameters of the crystal plasticity model were determined following different strategies for each alloy. In the case of IN718 Ni-based superalloy, they were obtained from compression tests in micropillars milled from grains of the polycrystal in different orientations suited for single, double (coplanar and non coplanar) and multiple slip. In the case of AZ31 Mg alloy, an inverse optimization strategy was developed to determine the single crystal properties from experimental results of the mechanical behavior of polycrystals.

This talk is part of the Engineering Department Bio- and Micromechanics Seminars series.

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