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

该学院早期职业发展（Career）项目将阐明通过称为马氏体相变的固-固相变具有可逆可调特性的材料所面临的长期挑战。例如，“可切换”多铁质材料具有独特的弹性、电和/或磁性，可以通过诱导马氏体相变可逆地“打开或关闭”。可切换多铁质材料激发了新的能量转换、能量收集和致动器技术，但滞后（工作能力损失）和功能疲劳或失效仍然是这些技术循环寿命要求的主要障碍。本研究的目的是通过多尺度、多模态的原位实验，促进对这些材料的力学迟滞和功能疲劳的理解。该奖项还将启动一个全面的教育和推广平台，主要有两个重点：(1)用于本科生和研究生课程的交互式扩展现实（XR）学习工具以及研究成果的传播；(2)物理/力学概念的实践演示，以供公众推广。这些演示还将通过底特律的夏令营，在为代表性不足的K-12学生举办的研讨会上使用。马氏体相变是许多不同材料的先进性能背后的使能机制，包括“可切换”的多铁体、钢、弹性体、高熵合金、超导体和许多材料在高应变速率下。由于马氏体相变的复杂性，理解这些行为是一个重大的科学挑战，与可逆马氏体相变相关的滞后和功能疲劳仍然是主要的技术障碍。本工作的目的是通过研究马氏体组织的循环激活和扩展来了解机械滞后和功能疲劳。该方法是在原位、三维和跨越五个数量级的长度尺度上解决潜在微观力学的层次性质，从单个界面的运动到数百个颗粒的聚集行为。这种多尺度方法将使用多模态3D/4D原位表征，包括暗场x射线显微镜、x射线拓扑层析成像和高能衍射显微镜对镁钪形状记忆合金进行表征。预期的结果是一个理解马氏体相变材料力学的新框架，该框架来自对应力激活习惯面变体选择的多尺度理解，结合了缺陷、界面应力场和微观结构可重复性的重要作用，并对势在必行的跨领域微观力学挑战具有广泛的意义。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.