CAREER: Understanding the Origins of Mechanical Hysteresis and Functional Fatigue in Martensitic Phase Transforming Materials

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

This Faculty Early Career Development (CAREER) project will elucidate long-lasting challenges facing materials that have reversibly tunable properties by way of a solid-to-solid phase transformation called martensitic phase transformation. For example, "switchable" multiferroics are materials that have distinct elastic, electric, and/or magnetic properties that can be reversibly "switched on or off" by inducing martensitic phase transformations. Switchable multiferroics have inspired novel energy conversion, energy harvesting, and actuator technologies, but hysteresis (loss of work capacity) and functional fatigue or failure remain major barriers for the cycle lifetime demands of these technologies. The goal of this research is to advance the understanding of mechanical hysteresis and functional fatigue in these materials through multiscale, multimodal in-situ experimentation. The award will also launch a comprehensive education and outreach platform with two main thrusts: (1) interactive extended reality (XR) learning tools for undergraduate and graduate courses as well as dissemination of research, and (2) hands-on demos on concepts of physics/mechanics for public outreach. These demos will also be used in workshops for underrepresented K–12 students through a Detroit-based summer camp. Martensitic phase transformations are the enabling mechanism behind the advanced performances of many diverse materials including "switchable" multiferroics, steels, elastomers, high entropy alloys, superconductors, and many materials at high strain rates. Due to the complexities of martensitic phase transformations, understanding these behaviors is a significant scientific challenge, and the hysteresis and functional fatigue associated with reversible martensitic transformations remain major technological barriers. The objective of this work is to understand mechanical hysteresis and functional fatigue by investigating the cyclic activation and propagation of martensitic microstructures. The approach is to resolve the hierarchical nature of the underlying micromechanics in situ, in 3D, and across five orders of magnitude in length scale, from the motion of the individual interfaces to the aggregate behavior of hundreds of grains. This multiscale approach will be achieved using multimodal 3D/4D in-situ characterization with dark-field X-ray microscopy, X-ray topo-tomography, and high-energy diffraction microscopy on magnesium-scandium shape memory alloys. The expected outcome is a new framework for understanding the mechanics of martensitic phase transforming materials that emerges from a multiscale understanding of stress-activated habit plane variant selection, incorporates the important role of defects, interfacial stress fields, and microstructural repeatability, and has broad implications for imperative cross¬cutting micromechanics challenges. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.