Elucidating the Impact of Nanoscale Strain and Concentration Fields on Martensitic Transformations in NiTiHf-based Shape Memory Alloys

阐明纳米级应变和浓度场对 NiTiHf 基形状记忆合金马氏体相变的影响

• 批准号: 2226478
• 负责人: Honggyu Kim
• 金额: $ 48.08万
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-11-01 至 2025-10-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2226478&HistoricalAwards=false
• 关键词: Elucidating; Impact; Nanoscale; Strain; Concentration

AbstractNON-TECHNICAL SUMMARYShape memory alloys (SMAs) are a unique class of alloys that can recover their original shape. This feature makes SMAs a leading contender for many future commercial and industrial technologies such as medical devices, sensors, actuators, and components for aerospace vehicles. Shape recovery in these metals relies on a reversible change in atomic arrangements. Designing and engineering their atomic structures can radically change their shape memory performance. Producing nano-sized particles, called precipitates, in SMAs offers a direct route to modifying their local atomic structure and chemistry, thereby achieving targeted shape memory properties. However, accurately pairing the characteristics and properties of nano-sized precipitates to shape memory performance remains a challenge due to a lack of high-precision, real-time measurements, which creates a roadblock to establishing a reliable alloy design for various applications. The PIs address this challenge by developing atomic-resolution, in situ electron microscopy techniques to quantitatively measure the impacts of precipitates on shape memory behavior in SMAs. The gained knowledge can generate powerful alloy design rules for precipitation-engineered SMAs for applications requiring high-temperature operations and improved mechanical properties. Moreover, the collaborative research activities between the PIs will be intertwined with educational programs and outreach activities through summer internships for underrepresented minority high-school students from local public schools, curriculum development targeting both on-campus students and distance-learning students (e.g., industry and military), and research training of graduate and undergraduate students with a strong emphasis on alloy design and materials characterization. These education plans promote student awareness about critical materials needs for new technologies and encourages diverse students to pursue careers in STEM. TECHNICAL SUMMARYMechanical and chemical effects of precipitates play a crucial role in controlling martensitic transformation (MT) dynamics in shape memory alloys (SMAs). However, there is a distinct lack of systematic and quantitative experimental evidence that can support, or test, theoretical models of the physical mechanisms of a MT modified by non-transforming coherent precipitates within the microstructure. This experimental program aims to quantify and elucidate the effects of nanoscale strain and concentration fields induced by coherent precipitates on the phase transformation and mechanical properties of NiTiHf-based SMAs. Specifically, the PIs seek to uncover and isolate the role of Heusler and Han phase precipitates (when they coexist), which have a distinctly different crystal structure and chemistry in NiTiHf-based SMAs. To achieve the goal, the PIs utilize a unique set of expertise in atomic-scale materials characterization based on aberration-corrected electron microscopy, electron diffraction, and in situ heating applications, as well as alloy design/synthesis and thermo-mechanical properties characterization. This program focuses on: (i) the development of alloy synthesis routes that allow for co-precipitation of Heusler and Han phases with controlled microstructure and chemistry; (ii) the quantification of strain and concentration fields around precipitates using atomic-resolution electron microscopy, spectroscopy, and scanning electron diffraction to uncover their effects on the microstructure morphology of the matrix; (iii) the characterization of the MT mechanisms in precipitation-strengthened SMAs and the phase transformation pathways using in situ temperature-controlled experiments for determining the dependence of a MT on the designed properties of precipitates (i.e., strain and concentration fields). This work provides a strong foundation for future SMA designs as well as in computational modeling by offering a quantitative, holistic understanding of the structure-composition-property relationships of SMAs and their dynamic response to realistic in-service environments.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.

摘要非技术摘要形状记忆合金 (SMA) 是一类独特的合金，可以恢复其原始形状。 这一特性使 SMA 成为许多未来商业和工业技术的领先竞争者，例如医疗设备、传感器、执行器和航空航天器组件。 这些金属的形状恢复依赖于原子排列的可逆变化。 设计和改造它们的原子结构可以从根本上改变它们的形状记忆性能。 在 SMA 中生产纳米级颗粒（称为沉淀物）提供了修改其局部原子结构和化学性质的直接途径，从而实现目标形状记忆特性。 然而，由于缺乏高精度、实时测量，将纳米级析出物的特性和性能与形状记忆性能精确配对仍然是一个挑战，这为为各种应用建立可靠的合金设计设置了障碍。 PI 通过开发原子分辨率的原位电子显微镜技术来定量测量沉淀物对 SMA 形状记忆行为的影响，从而应对这一挑战。 所获得的知识可以为沉淀工程 SMA 生成强大的合金设计规则，适用于需要高温操作和改进机械性能的应用。 此外，PI 之间的合作研究活动将与教育计划和外展活动交织在一起，通过为当地公立学校代表性不足的少数族裔高中生提供暑期实习、针对在校学生和远程学习学生（例如行业学生）的课程开发和军事），以及研究生和本科生的研究培训，重点是合金设计和材料表征。 这些教育计划提高学生对新技术关键材料需求的认识，并鼓励多元化的学生从事 STEM 职业。技术摘要沉淀物的机械和化学效应在控制形状记忆合金 (SMA) 的马氏体相变 (MT) 动力学方面发挥着至关重要的作用。 然而，明显缺乏系统和定量的实验证据来支持或测试由微观结构内的非相变相干析出物修饰的 MT 物理机制的理论模型。 该实验计划旨在量化和阐明相干沉淀物引起的纳米级应变和浓度场对 NiTiHf 基 SMA 相变和机械性能的影响。 具体来说，PI 试图揭示和分离 Heusler 和 Han 相沉淀物（当它们共存时）的作用，它们在 NiTiHf 基 SMA 中具有明显不同的晶体结构和化学性质。 为了实现这一目标，PI 在基于像差校正电子显微镜、电子衍射和原位加热应用的原子级材料表征以及合金设计/合成和热机械性能表征方面利用了一套独特的专业知识。 该计划的重点是：（i）开发合金合成路线，允许在受控的微观结构和化学条件下共沉淀 Heusler 和 Han 相； (ii) 使用原子分辨率电子显微镜、光谱学和扫描电子衍射对沉淀物周围的应变和浓度场进行量化，以揭示它们对基体微观结构形态的影响； (iii) 沉淀强化 SMA 中 MT 机制的表征以及使用原位温度控制实验的相变路径，以确定 MT 对沉淀物设计特性（即应变和浓度场）的依赖性。 这项工作通过提供对 SMA 的结构-成分-性能关系及其对实际使用环境的动态响应的定量、全面的理解，为未来 SMA 设计以及计算建模奠定了坚实的基础。该奖项反映了 NSF 的法定使命通过使用基金会的智力价值和更广泛的影响审查标准进行评估，并被认为值得支持。