Materials World Network: Collaborative Research: Modeling Ferroelastic Strain Glasses

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This joint project between Ohio state University (OSU), the University of Pennsylvania (UPenn), and the National Institute for Materials Science (NIMS) in Japan combines critical experiments from the Japanese side with multi-scale modeling and simulation from the U.S. side to understand and predict the nanoscale mechanisms underlying the effects of point defects on the thermodynamics and initiation and propagation kinetics of martensitic transformations (MTs). In collaboration with the partner institution in Japan on processing, testing and characterization of shape memory alloys and strain glasses, the US participants address fundamental questions of long standing interest concerning MTs and the effects of point defects, such as what elementary defect and defect process constitute the smallest unit of MT, what the activation pathway and barrier energy of these elementary defect processes are, and how point defects modify them. In particular, the investigators systematically probe the effects of random point defects on the multi-plane generalized stacking fault (MGSF) energy landscape along the minimum energy pathway (MEP) connecting the parent phase lattice to the martensitic phase lattice and on the vibrational entropies, which together constitute the crystalline free energy that replaces the phenomenological Landau free energy. A new microscopic phase field model of MTs based on the ab initio energetics and a reaction-coordinate theory will be tested. The methodology and approach to be developed are rather general and applicable to a larger set of shear-dominated processes such as the displacive-diffusional transformations found in many advanced alloy systems and the shearing-reordering process during plastic deformation of ordered alloys. Computational tools developed will be disseminated widely through free download from the project website. The educational effort involving the exchange of graduate students, postdoctoral researchers and faculty will inject cutting-edge development in materials science and technology and provide a broad international perspective to the student curricula.