Super Responses of Decomposed Two-Phase Nanodispersions to External Stimuli: Theory and Modeling

该奖项支持材料新功能的理论和计算研究，重点是对外加应力、磁场和电场的巨大低滞后可恢复应变响应。在传统的沉淀硬化合金中，当它们是由嵌入在立方基体中的低对称性相的沉淀组成的两相纳米分散体时，这种效应是预期的。在分解的早期阶段形成的低对称相的沉淀是具有几种对称相关取向变体之一的单畴颗粒。应变响应是由析出相的不同取向变体之间的相干切换引起的。这是一种新的效应。开关产生的宏观应变与本征响应相比是巨大的。如果施加的场是应力，则材料变成超弹性；如果是磁场，则材料成为外在超磁致伸缩器。本项目将研究可能导致沉淀硬化合金在应用领域产生巨大的低迟滞应变响应的条件。该项目的科学目标是为寻找合金系统和加工条件制定蓝图，以提供这些系统的特殊功能特性。该项目的目标是提供一种具有独特机械和功能特性组合的新型功能材料。本项目的具体目标包括：发展理论和计算机模型，明确考虑所有影响可恢复应力和/或磁场诱导单畴取向变异体切换的物理显著能量贡献，从而考虑宏观应变响应。2. 阐明控制具有纳米沉淀物柔性取向变体的相干两相材料体系形成的机制。特别是，对弹性模量、晶格失配和组成相的磁结构耦合的影响的理解的发展，以及热机械/热磁处理效果的优化。3. 在不同方向的外加应力和/或磁场下建立微观结构和动态应变响应之间的相关性。该奖项还提供支持，将使：(1)进一步与实验家合作，以验证我们的发现，并寻找这类先进的功能材料，（ii）下一代材料研究人员的教育和培训。该奖项支持对分解纳米结构材料的功能行为的实际未知领域的探索。纳米分散分解体系是技术上重要的结构材料，几十年来一直是一个深入研究的课题。然而，这些材料有一个非常重要的方面是以前被忽视的：在一定条件下，沉淀硬化的纳米分散体可以获得独特的功能特性。材料对外部刺激具有巨大的可恢复应变响应，可解释为超弹性、超磁致伸缩、形状记忆和铁磁记忆效应。这项理论和计算研究的目标是：(i)研究这些类型的材料在分解过程中的形成和优化其性能的方法，（ii）研究它们的开关诱导应变响应的机制和动力学，以及（iii）为工程设计一类自发形成的廉价功能材料制定蓝图，这些材料具有对施加应力，电场和磁场的期望超级响应。该项目有潜力打开一个实际上尚未开发的超响应功能材料的来源。特别是，它的成功将为开发具有显著增强磁机械性能的材料开辟一条道路，并设计出廉价的磁致伸缩合金，这种合金不含难以获得的关键稀土元素，但仍具有与稀土基化合物相当甚至超过它们的理想性能。该奖项还支持教育和培训博士后研究助理和研究生的教育活动，为21世纪材料研究的挑战做好准备，这将需要跨学科的方法和物理和工程不同分支之间的协同作用。

TECHNICAL SUMMARYThis award supports theoretical and computational investigations of new functionalities in materials with a focus on giant low hysteretic recoverable strain response to applied stress, magnetic and electric fields. This effect is expected in traditional precipitation hardened alloys when they are two-phase nanodispersions consisting of precipitates of a low-symmetry phase embedded in a cubic matrix. The precipitates of a low-symmetry phase formed at the early stages of decomposition are single domain particles that have one of several symmetry-related orientation variants. The strain response is caused by coherent switching between different orientation variants of the precipitates. This is a new effect. The switching- generated macroscopic strain is giant in comparison with the intrinsic responses to the applied fields. If the applied field is stress, the material becomes superelastic; if it is a magnetic field, the material becomes an extrinsic super-magnetostrictor. This project will investigate conditions that could lead to a giant low hysteretic strain response of precipitation hardened alloys to the applied fields. The scientific goal of the project is to develop a blueprint for the search of alloy systems and the processing conditions that would provide exceptional functional properties of these systems. The goal of this project is to provide access to a new class of functional materials with unique combinations of mechanical and functional properties. Specific goals of this project include: 1. Developing theories and computer models that can explicitly take into considerations all physically significant energy contributions affecting the recoverable stress and/or magnetic field-induced switching of single-domain orientation variants and thus macroscopic strain response. 2. Clarifying mechanisms that control the formation of coherent two-phase material systems with flexible orientation variants of nanoprecipitates. In particular, the development of the understanding of the effects of elastic moduli, lattice mismatch, and magneto-structural coupling of the constituent phases, as well as the optimization of the effects of thermo-mechanical/ thermo-magnetic treatments. 3. Establishing correlations between the microstructure and dynamic strain responses to differently directed applied stress and/or magnetic fields. This award also provides support that will enable: (1) further collaboration with experimentalists in order to validate our findings and search for advanced functional materials of this kind, (ii) the education and training of the next generation of materials researchers.NON- TECHNICAL SUMMARYThis award supports an exploration of the practically uncharted territory of the functional behavior of decomposed nanostructured materials. Nanodispersive decomposed systems are technologically important structural materials that have been a subject of intensive research for decades. However, there are very important aspects of these materials that have been previously overlooked: under certain conditions, the precipitation hardened nanodispersions can acquire unique functional properties. The materials can have giant recoverable strain responses to the external stimuli, which can be interpreted as superelasticity, super magnetostriction, shape memory and ferromagnetic memory effects. The goal of this theoretical and computational research is to: (i) investigate the formation of these kinds of materials during decomposition and ways to optimize their properties, (ii) study the mechanisms and dynamics of their switching-induced strain responses, and (iii) develop a blueprint for engineering a new class of spontaneously formed inexpensive functional materials with desired super responses to applied stress, electric, and magnetic fields. The project has the potential to open a practically untapped source of super-responsive functional materials. In particular, its success would open a way to develop materials with dramatically enhanced magneto-mechanical properties, and to engineer inexpensive magnetostrictive alloys that are free from critical rare-earth elements that are difficult to obtain, but still have desired properties comparable or even exceeding those of rare-earth based compounds.This award also supports educational activities to educate and train a postdoctoral research associate and graduate students, preparing them for the challenges of materials research in the 21st century which will require an interdisciplinary approach and synergy between different branches of physics and engineering.