MAGIKID

This project focuses on three iron-base alloys that have growing potential for high-temperature, high-strength and strong- magnet applications: Fe-Cr, Fe-Mn and Fe-Co. Because of the key role of magnetism, an innovative materials design based on advanced modeling approaches is necessary to control key properties of these materials. Such a design strategy requires the combination of (i) highly accurate methods to determine atomic features with (ii) efficient coarse-graining techniques to access target physical properties and to perform the screening of materials compositions. For the former, density functional theory (DFT) has for many materials classes already proven to be a highly successful tool. For Fe-based alloys, however, a critical bottleneck is the role that magnetic ordering, excitations and transitions have on thermodynamic, defect and kinetic properties. Therefore, a complete and accurate modeling of magnetism is urgently needed to address the materials-design challenges: the resistance to radiation damage related to the chemical decomposition in Fe-Cr, the grain-boundary embrittlement in ferritic Fe-Mn and the high-strength of austenitic Fe-Mn, and the phase ordering and the relative stability of a and ? phases in Fe-Co cannot be fully understood without properly accounting for the magnetic effects. The novelty of the current approach is twofold: First, on the DFT-side, we will make use of the recent important progress in treating magnetism in pure idealized Fe lattices, in order to go towards an accurate modeling of magnetic multi-component systems with point/extended defects, and beyond the standard collinear approximation. Second, we will develop new methods that allow us to bridge the gap between (i) highly accurate electronic calculations and (ii) large-scale atomistic thermodynamic and kinetic simulations for iron based alloys by – and this is decisive – fully taking into account the impact of magnetism on defect properties, diffusion and microstructural evolution. For the latter, lattice-based effective interaction models (EIMs) and tight-binding (TB) models will be developed based on data from DFT, including magnetic configurations, excitations and transitions. This will allow us to provide a coherent description of the role of magnetism on various properties of Fe-based alloys at different length scales and at finite temperature. It will further give us the ability to perform the optimization of key parameters controlling the relevant properties like phase decomposition in Fe-Cr, phase ordering in Fe-Co or decohesion of grain boundaries in Fe-Mn. Dedicated experiments in bulk alloys and along intergranular / interphase boundaries grown on demand will be performed in the project, which are essential for verifying the robustness of the theoretical predictions. The three chosen alloys exhibit a large variety of magnetic behavior. The methods developed and applied in this proposal are therefore expected to be transferrable to the modeling of other magnetic materials. The results of our simulations will lead to the improvement of thermo¬dynamic and diffusion databases and tools (such as DICTRA) that are nowadays routinely used in industrial R&D but that at present have difficulties in accounting for magnetism. In this way a better and more systematic understanding of the role of magnetism in Fe-based alloys will help to improve significantly the predictive power of the simulations and thus contribute to a more efficient and accurate development of new steel grades. Once fully implemented, the availability of such computational tools is expected to boost the efficiency, change the strategy in designing new steel grades and to form an important contribution for the future competitiveness of steelmakers.