NSF/DMR-BSF: Twin boundary structure and mobility in shape memory alloys

Non-technical Abstract

This project extends the fundamental understanding of how materials deform and provides valuable information for the development of novel and improved alloys. Active or 'smart' materials such as those in this work find applications in medicine (e.g. stents and tooth braces), vehicles (including automobiles, aircrafts, and spacecraft), and in micro-electro-mechanical systems (MEMS).

This is an international collaboration between a US team at Boise State University, Boise, Idaho, and an Israeli team at the Technion in Haifa, Israel. The project enhances the basic understanding of alloy deformation and develops an educated workforce in this area. This promotes the Idaho economy, with one of the lowest gross domestic product per capita in the US. Also, the US team will promote education, science, and diversity by continuing a tradition of visiting local K-12 school and using institutional channels for recruiting students from underrepresented minorities. Undergraduate students and secondary education teachers will gain research experience through a Boise State Research Experience for Undergraduates (REU) site. The team will disseminate results through peer-reviewed journals, websites, conferences, and seminars.

Part 2: Technical description of the project

This NSF-BSF collaborative research project which includes a US research team at Boise State University, Boise, Idaho, and an Israeli research team at the Technion, Haifa, extends the fundamental understanding of how materials respond to dynamical loading. In particular, research focuses on deformation by twinning, besides dislocation mediated deformation one of the major modes of plastic deformation. While the dynamical properties of dislocations have been well studied, a corresponding knowledge for twin boundaries does not exist though it is highly needed for the advancement of modern materials including high strength structural materials, nanocrystalline materials, nanoscale materials, and functional materials to align with the Materials Genome Initiative. The international team aims to correlate the dynamical properties of twin boundaries (TBs) to their atomistic structure, which includes topological defects such as twinning disconnections (TDs). Researchers will use novel experimental and analytical models to: (1) characterize twin boundary structures, (2) establish twin boundary defect models for type I and type II twins, (3) measure the complete kinetic relation of twin boundary motion, (4) develop analytical models for twin boundary motion, and (5) formulate relations between structural properties of twin boundaries and the dynamics of the twinning process. This research program proposes to advance knowledge in materials science and physics through a comprehensive theoretical and experimental study of the relationships between the atomistic structures of TBs and TDs; barriers and mechanisms for TB and TD motion; and kinetic relations for TB motion. The team will study these topics in three different martensite structures and three different types of twins (compound, type I and type II). Results are expected to facilitate accurate models of the complicated structures of TBs of type I and II twins, and the kinetic relations of the TBs. Results will be significant as they will apply to all materials that deform by twinning including intermetallic compounds, ferroelectric ceramics, shape memory alloys, and metals. Both US and Israeli PIs have complementary research projects on related subjects that will benefit from project results. Specifically, the American PI is conducting twinning and fatigue research including NSF-funded work. The Israeli PI has an ISF project on twinning dynamics in ferroic materials, which has one year of overlap with the proposed program. The experienced international team has the required know how and resources to carry out the proposed work.