Ab Initio Approaches to Martensitic Transformations in Metallic Alloys

点击翻译按钮获取中文摘要

TECHNICAL SUMMARYThis award supports theoretical and computational research that is focused on developing and using first principles methods to compute free energies for various competing mechanisms of martensitic transformations. These diffusionless displacive transformations which occur in a wide variety of metals, semiconductors, and ceramics, play a special role in materials science. They constitute the fundamental strengthening mechanism of steels and are directly responsible for the shape memory effect and superelasticity in shape memory alloys. The PI will develop and implement efficient ab initio methods based on density functional theory that will allow for accurate calculations of electronic, vibrational, and magnetic entropy contributions to the free energies of various martensitic transformation paths. Specifically, the main objectives are:(1) Calculation of free energies and entropies of metastable and experimentally unstable phases, which will provide a valuable database for phase diagram calculations of multi-component alloys, (2) Calculation of thermodynamics of high-temperature martensitic transformation paths in iron, which will simultaneously include vibrational and spin disorder entropies, (3) Development of efficient methods for calculating free energy barriers and first-principles derived Landau-type free energy functionals for common martensitic transformation paths in high-temperature shape memory alloys, and (4) Development of new methods for treating composition effects on thermodynamics of martensitic transformations.Successful completion of the proposed research program will lead to better understanding of the thermodynamic driving forces and microstructural mechanisms of martensitic transformations, hence providing fundamental basis for rational design of new high-temperature shape memory alloy systems.This award also supports the education of graduate students and the introduction of undergraduate students to modern computational methods. The PI will partner with the California NanoSystems Institute and the Center X to leverage their ongoing efforts to increase participation of minority students and members of underrepresented groups in engineering, science, and technology. The research will also aid in the improvement of computational science instruction aids via the development of high-throughput molecular dynamics simulations, which is a software platform that aims to streamline the process of performing molecular dynamics simulations. The software to be developed will be disseminated freely through the PI's group website.NON-TECHNICAL SUMMARY This award supports theoretical and computational research that is focused on developing and using parameter-free methods for elucidating the fundamental mechanisms of a special class of transformations, called "martensitic", that occur in some types of solids. In martensitic transformations, atoms arranged in a particular initial order diffuse by relatively small amounts compared to their interatomic distance, in a cooperative and homogeneous movement, resulting in a new atomic arrangement with a different shape or symmetry. These transformations are both scientifically and technologically important, as they constitute the fundamental strengthening mechanism of steels, and they are directly responsible for the shape memory effect, wherein a deformed alloy "remembers" its original, cold-forged shape and returns to it when heated. The PI will develop and implement efficient computational methods that will allow for calculating various contributions that stabilize atomic arrangements along martensitic transformation paths. Successful completion of the proposed research program will lead to better understanding of the thermodynamic driving forces and atomistic mechanisms of martensitic transformations, hence providing fundamental basis for the rational design of new high-temperature shape memory alloy systems.The educational component of this award involves the education of graduate students and the introduction of undergraduate students to modern computational methods. The PI will partner with the California NanoSystems Institute and the Center X to leverage their ongoing efforts to increase participation of minority students and members of underrepresented groups in engineering, science, and technology. The research will also aid in the improvement of computational science instruction aids via the development of high-throughput molecular dynamics simulations, which is a software platform that aims to streamline the process of performing computer simulations of physical movements of atoms or molecules interacting with each other. The software to be developed will be disseminated freely through the PI's group website.