CAREER: Interface Deformation and Compatibility in Shape Memory Polycrystals

形状记忆合金（SMA）是一种独特的多功能相变材料。 它们可以通过可逆的马氏体相变在热循环或机械循环下在两种形状之间切换，并且在传感、致动、能量转换和收集以及阻尼等方面有应用前景。 这个CAREER项目连接了两个迄今为止独立的研究领域，（i）晶界科学与工程和（ii）SMA中的位移马氏体相变，并试图了解双相SMA多晶中马氏体相变过程中界面之间的机械相互作用。 本研究将利用实验、解析理论和介观尺度计算模拟来探讨两种主要的界面效应：（1）晶界晶体学特征对晶界处应变传递、调节和相容性的影响;（2）非转变的、沿沿着晶界析出的韧性相如何调节来自跨相界的转变应变。 将探索晶界工程以增强晶界处的应变相容性，从而提高SMA多晶的延展性和适用性。 在本研究中获得的界面处的应变传递和相容性的基本理解也将与许多其他多晶金属和化合物中的类似问题相关。 非技术总结：形状记忆合金（SMA）是一种独特的多功能材料。它们可能由于沿内部平面缺陷或称为晶界的界面的沿着脆性断裂而失效，并且该问题显著地限制了它们的适用性。 本项目将通过执行以下操作来定量阐明SMA故障的机制： 实验表征和计算建模。 这项工作还将利用晶界工程策略来改善晶界性能，提高SMA的延展性，这将使SMA在商业和军事领域的先进技术中得到实际应用。 该项目还将涉及大量的教育和外联工作。 教育活动包括改造本科生和研究生核心机械性能课程，促进计算材料课程，培养本科生和研究生研究人员，他们将成为机械性能，金属和计算材料科学的专家和领导者。 外联活动将吸引年轻学生学习科学和工程学，促进公众对工程学的兴趣，并支持女工程学学生的专业发展和提高。

Technical Summary:Shape Memory Alloys (SMAs) are unique multifunctional phase-change materials. They can switch between two shapes under thermal or mechanical cycling by a reversible martensitic phase transformation, and are promising for applications in sensing, actuation, energy conversion and harvesting, and damping. This CAREER project bridges two thus far separate research areas, (i) grain boundary science and engineering and (ii) displacive martensitic transformations in SMAs, and seeks to understand mechanical interactions across interfaces during martensitic transformations in dual-phase SMA polycrystals. This research will use experiments, analytical theory, and mesoscale computational modeling to explore two major interface effects: (1) the effects of grain boundary crystallographic character on strain transfer, accommodation, and compatibility at grain boundaries; (2) how a non-transforming, ductile phase precipitated along grain boundaries accommodates transformation strains from across phase boundaries. Grain boundary engineering will be explored to enhance strain compatibility at grain boundaries, thereby improving the ductility and applicability of SMA polycrystals. The fundamental understanding on strain transfer and compatibility at interfaces gained in this research will also be relevant to similar problems in many other polycrystalline metals and compounds. Non-Technical Summary:Shape Memory Alloys (SMAs)are unique multifunctional materials. They can fail by brittle fracture along internal planar defects or interfaces called grain boundaries and this problem has significantly limited their applicability. This project will quantitatively elucidate the mechanisms for failure in SMAs by performing experimental characterizations and computational modeling. This work will also exploit grain boundary engineering strategies to improve grain boundary properties and enhance the ductility of SMAs, which will enable practical applications of SMAs in advanced technologies in both commercial and military sectors. This project will also involve substantial education and outreach efforts. The education activities include transforming both undergraduate and graduate core mechanical properties courses, contributing to computational materials course, and training undergraduate and graduate researchers who will become experts and leaders in mechanical properties, metals, and computational materials science. The outreach activities will attract young students to science and engineering, promote public interest in engineering, and support professional development and advancement of women engineering students.