Collaborative Research: Compositionally and Structurally Modulated Ferroelastic Films for Unprecedented Superelastic Properties

合作研究：成分和结构调制的铁弹性薄膜，具有前所未有的超弹性特性

• 批准号: 2333552
• 负责人: Jagannathan Rajagopalan
• 金额: $ 42.54万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-02-01 至 2027-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2333552&HistoricalAwards=false
• 关键词: Collaborative; Research; Compositionally; Structurally; Modulated

NON-TECHNICAL SUMMARYMost metals and metallic alloys become permanently deformed even when they are stretched or compressed by a small amount (typically less than 1%). In contrast, a special category of materials known as Shape Memory Alloys (SMAs) can regain their original shape even after undergoing large deformations (up to 10%) once the loads are removed. This unique property of SMAs has led to a broad array of applications ranging from medical implants and robotics to flexible airplane wings and space exploration vehicle tires. However, the mechanical behavior of SMAs is highly non-linear, i.e., their deformation can increase drastically even for small changes in force, which can make them mechanically unstable. In addition, significant amounts of energy are wasted as heat when the SMAs recover their shape after being deformed. The primary goal of this integrated experimental and computational research project is to eliminate the undesirable mechanical instability and create SMAs that are more energy efficient. This is being accomplished by systematically modulating the chemical composition and structure of the SMAs at the nanoscale. This novel alloy design approach, termed as Nanoscale Compositional and/or Structural Modulation (NCSM), can be used to create not only mechanically stable and energy efficient SMAs but also other types of materials with highly tunable mechanical properties such as titanium-based alloys for bone implants that mimic the strength and stiffness of natural bones. The NSCM alloy design strategy, unique experimental processing and characterization techniques, and state-of-the-art computer simulation methodologies developed in this project are being broadly disseminated via conference talks, online tutorials, and articles in academic journals. The project is also advancing educational outreach and workforce development through hands-on demonstrations to high school students, recruitment of underrepresented minority students for conducting research and workforce training partnerships with regional community colleges and industries. TECHNICAL SUMMARYThe elastic strain limit of most metals and alloys is less than 0.5%, except for whiskers or freestanding nanowires. Ferroelastic materials such as shape memory alloys (SMAs), in contrast, can achieve giant recoverable strains of up to ~10%. However, the inherent nonlinearity of pseudo-elasticity in SMAs results in mechanical instability, characterized by strain avalanche driven stress plateaus and substantial stress-strain hysteresis. This integrated computational and experimental research project is addressing this pivotal issue by introducing an innovative approach, termed as Nanoscale Compositional and/or Structural Modulation (NCSM), to the design and synthesis of the next generation of SMAs. The NCSM concept capitalizes on the strong dependency of the critical stress for stress-induced martensitic transformation (MT) in NiTi SMAs on composition and grain size to eliminate strain avalanches during MT, and thus enable controlled strain release. The central hypothesis is that nanoscale modulations in chemical composition and microstructure will introduce confinements to the MT process, effectively suppress autocatalysis and fundamentally change the MT characteristics, leading to NiTi SMAs that are strong, linear superelastic, hysteresis-free, and have ultralow modulus. This hypothesis is being tested by synthesizing NCSM NiTi films with precisely defined nanoscale compositional and grain size modulations using physical vapor deposition, and characterizing their mechanical behavior using MEMS based tensile testing. The design of these NCSM NiTi films is being guided by computational modeling using molecular dynamics and phase field simulations. It is anticipated that this new class of NCSM SMAs can be designed to exhibit a wide array of highly tunable stress-strain behaviors that are desirable for a variety of advanced biomedical, functional, and structural applications. Although the focus of the project is on NiTi SMA, the NCSM alloy design concept is applicable to a broad class of materials for which structural phase transformations are utilized to tailor the properties.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.

大多数金属和金属合金即使受到少量拉伸或压缩（通常小于1%）也会发生永久性变形。相比之下，一种被称为形状记忆合金（sma）的特殊材料，即使在经历了很大的变形（高达10%）后，一旦载荷被移除，也能恢复其原始形状。sma的这种独特特性导致了广泛的应用，从医疗植入物和机器人到柔性飞机机翼和空间探索车辆轮胎。然而，sma的力学行为是高度非线性的，即即使力的微小变化，它们的变形也会急剧增加，这可能使它们在机械上不稳定。此外，当sma变形后恢复形状时，大量的能量被浪费为热量。这个综合实验和计算研究项目的主要目标是消除不良的机械不稳定性，并创造出更节能的sma。这是通过在纳米尺度上系统地调节sma的化学成分和结构来实现的。这种新颖的合金设计方法，被称为纳米级成分和/或结构调制（NCSM），不仅可以用于制造机械稳定和节能的sma，还可以用于制造具有高度可调机械性能的其他类型的材料，例如用于骨植入物的钛基合金，它可以模仿天然骨骼的强度和刚度。在这个项目中开发的NSCM合金设计策略、独特的实验加工和表征技术以及最先进的计算机模拟方法正在通过会议演讲、在线教程和学术期刊上的文章广泛传播。该项目还通过向高中生进行实际演示、招募代表性不足的少数民族学生进行研究以及与地区社区学院和行业建立劳动力培训伙伴关系等方式，推进教育推广和劳动力发展。技术概述：除晶须或独立纳米线外，大多数金属和合金的弹性应变极限小于0.5%。相比之下，形状记忆合金（sma）等铁弹性材料可以实现高达~10%的巨大可恢复应变。然而，SMAs伪弹性固有的非线性导致其力学不稳定，表现为应变雪崩驱动的应力高原和严重的应力-应变滞后。这个综合计算和实验研究项目通过引入一种创新方法来解决这一关键问题，称为纳米级成分和/或结构调制（NCSM），用于设计和合成下一代sma。NCSM概念利用NiTi sma中应力诱导马氏体相变（MT）的临界应力对成分和晶粒尺寸的强烈依赖性来消除MT过程中的应变雪崩，从而实现可控的应变释放。该研究的核心假设是，纳米级的化学成分和微观结构调制将给MT过程带来限制，有效地抑制自催化作用，并从根本上改变MT特性，从而使NiTi sma具有强、线性超弹性、无迟滞和超低模量。这一假设正在通过物理气相沉积合成具有精确定义的纳米级成分和晶粒尺寸调制的NCSM NiTi薄膜，并使用基于MEMS的拉伸测试来表征其力学行为来验证。这些NCSM NiTi薄膜的设计是由分子动力学和相场模拟的计算模型指导的。预计这种新型NCSM sma可以被设计成具有广泛的高度可调的应力应变行为，这对于各种先进的生物医学、功能和结构应用是理想的。虽然该项目的重点是NiTi SMA，但NCSM合金设计概念适用于广泛的材料类别，这些材料利用结构相变来定制性能。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。