CAREER: Heterogeneous Nucleation in Reversible Martensitic Transformations

非技术总结：一些固体经历可逆相变，这涉及到原子的重排和键的扭曲，导致材料的形状和性质的变化。这种特性可用于开发紧凑高效的执行器、传感器和各种微电子器件。结构转变开始于材料的缺陷或缺陷附近，这有利于原子的重新排列。然而，当考虑小体积材料的转换时，遇到这种罕见缺陷的概率很低，导致不可预测和低效的操作。在极端情况下，这可能会完全阻止转换的发生。这个项目的目的是了解缺陷在启动结构转换中所起的作用，并找到一种将这些缺陷引入材料的方法。这将允许在微米和纳米长度尺度上操作设备。该提案的更广泛目标包括开发可分发的交互式材料科学实验（“盒子里的实验室”），可以远程执行，以吸引远程学生。此外，该提案将通过有针对性的UG研究机会和与拟议研究相关的具有社会影响力的工程设计挑战，吸引本科生（UG）学生，特别是来自社区学院的转校生。技术概述：无扩散固态相变通常由晶格中稀疏的高能原子尺度缺陷成核。材料科学的一个重大挑战是理解如何利用材料的异质性和无序性来影响材料的性能。特别是，虽然马氏体相变（MTs）中异质成核的位错缺陷模型相当发达，但点缺陷团簇的作用知之甚少，尽管最初观察到辐照诱导的缺陷团簇可以作为有效的成核位点。本研究的结果将推动MTs成核科学的发展：1)通过测量天然成核位点的数量密度作为热力学驱动力的函数，并确定晶格相容性在控制尺寸依赖的成核行为中的作用；2)通过实验量化辐照诱导缺陷团簇和He纳米气泡的效力。这些观察结果将用于开发和测试基于缺陷簇的MT成核模型。该提案的教育成果将影响UG工程教育目前正在进行的两个范式转变：1)更广泛地采用主动学习方法，以及2)有效且可扩展的远程教育方法。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。

Non-Technical Summary:Some solids undergo reversible phase transformations, which involve the rearrangement of atoms and the distortion of bonds, resulting in changes to the shape and properties of a material. This behavior can be used to develop compact and efficient actuators, sensors, and a variety of microelectronic devices. Structural transformations start near a defect or imperfection in a material, which facilitates the rearrangement of atoms. However, when considering transformations in small volumes of material, the probability of encountering such a rare defect is low, resulting in unpredictable and inefficient operation. In extreme cases, this can stop the transformation from occurring entirely. This project's aims are to understand the role that defects play in initiating structural transformations, and to find an approach to introduce such defects into a material. This would allow the operation of devices at micrometer and nanometer length-scales. The broader objectives of this proposal include developing distributable interactive materials science experiments ('lab in a box') that can be performed remotely to engage distance students. Additionally, this proposal will engage undergraduate (UG) students, and in particular transfer students from community colleges, through targeted UG research opportunities and through societally impactful engineering design challenges related to the proposed research.Technical Summary:Diffusionless solid-state phase transformations generally nucleate from sparse, high energy atomic-scale defects in the crystal lattice. One of the grand challenges in materials science is understanding how material heterogeneity and disorder can be harnessed to influence the properties of materials. In particular, while dislocation defect models of heterogeneous nucleation in martensitic transformations (MTs) are fairly well-developed, the role of clusters of point defects is very poorly understood, despite initial observations that irradiation induced defect clusters can serve as potent nucleation sites. The outcomes of this study will advance the science of nucleation of MTs 1) by measuring the number density of native nucleation sites as a function of thermodynamic driving force, and determining the role of lattice compatibility in governing size-dependent nucleation behavior, and 2) by experimentally quantifying the potency of irradiation-induced defect clusters and He nanobubbles. These observations will be used to develop and test a defect-cluster based MT nucleation model. The educational outcomes of this proposal will impact two paradigm shifts currently underway in UG engineering education: 1) broader adoption of active learning methods, and 2) effective and scalable approaches to distance education.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.