Grain refinement during EAP as studied by atomistic simulations. a) Refined grain structure as identified by Orisodata; b) Defect structure in the sample. Only non-fcc atoms are shown; c) Dislocation structure at a low angle grain boundaries in the sample. Partial and full dislocations are colored green and blue, respectively. All other dislocations are stair-rod dislocations.

Background: Severe plastic deformation (SPD) processes are forming techniques that impose large plastic strains to achieve ultra-fine grained and nanocrystalline microstructures. The refined microstructure results in a significant increase in strength and in many cases without a considerable loss in ductility. Despite their long existence, a comprehensive understanding of the deformation and grain refinement mechanisms during SPD is still lacking.

Goals: The overarching goal of the project is to obtain insights into fundamental dislocation processes and grain refinement mechanisms during severe plastic deformation. To this end we use large scale atomistic simulations to model the equal channel angular pressing process. The results of the simulations are analyzed using in-house developed machine learning and data science algorithms. This novel combination of simulation techniques and machine learning based analysis methods is the key to provide a detailed mechanistic understanding of the complex processes in the microstructure.