GOALI: Micromechanics Experiments and Modeling of Shape Memory Response in Ni-Ti Based Alloys

技术概述：形状记忆合金是具有源于马氏体转变的显著特性的材料。形状记忆和伪弹性行为的一个基本方面是没有很好地理解的是，矩阵如何适应与转换相关的大应变。从理论上讲，调节可以通过基质可塑性或诱导其他转化变体来实现。这项为期三年的GOALI提案将与GM Research合作，对几种Ni-Ti基合金（包括三元Ni-Cu-Ti）的伪弹性形状记忆行为进行新的基本见解。重点将放在合金，经历不同的马氏体转变，并表现出不同的功能疲劳性能。该方法将创新的微米级机械测试和先进的微观结构表征与分析和新颖的基于微观结构的建模相结合。聚焦离子束加工的微晶的单轴变形将用于探测作为基质晶体取向的函数的静态和循环响应，并且为了直接测量各个变体的机械响应（应力、应变、功输出）。使用透射电子显微镜对残留子结构进行死后表征，将与可能的转换的分析建模相结合。这种方法也将直接产生马氏体相变与基体塑性的相对条件，在一定范围内的组件尺寸。一种新的基于微观结构的有限元方法将被开发，明确跟踪本地，离散相变耦合率依赖晶体塑性。这将是第一次，这将使治疗的大小效应和产生的局部可塑性与转换？理解和增强伪弹性和形状记忆响应的关键一步。拟议的努力集成了先进的表征在俄亥俄州州立大学和通用汽车研究中心与新的实验技术在两个能源部实验室？在橡树岭国家实验室进行的高温纳米压痕/柱测试和在国家电子显微镜中心进行的原位柱测试。非技术性概述：形状记忆合金（SMA）是具有显著特性的材料，这些特性包括在施加载荷下大范围地弯曲和拉伸的能力，然后当载荷移除时弹回到它们的原始形状。此外，SMA在加热时可以改变形状，之后它们可以保持新获得的形状，或者在冷却回室温后恢复到原始形状。汽车行业已经认识到SMA的巨大潜力，因为与传统的电动执行器相比，它们是非常简单的致动装置。例如，它们可以被用作小，？固态？电动机可用于重新配置各种组件，大大降低了此类系统的复杂性。然而，市售的SMA材料由于在经历许多温度或应力循环后其形状改变能力的退化而目前没有以其全部潜力运行（？功能性疲劳？）。该计划旨在发展与此降解过程相关的材料科学方面的基本理解，以及建模能力的发展，以预测和改善汽车，医疗和其他应用的功能疲劳性能。俄勒冈州立大学和通用汽车公司之间的一个强有力的交流计划将刺激知识的有效转移，并将提供充分的机制，体验学术和工业环境。在一个令人兴奋的推广工作中，我们将开发一个关于形状记忆合金及其应用的高中探究式教学模块。还确定了若干机制，确保将这一模块纳入地方高中。

TECHNICAL SUMMARY:Shape memory alloys are materials with remarkable properties that stem from a martensitic transformation. One of the fundamental aspects of shape memory and pseudoelastic behavior that is not well understood is how the matrix accommodates the large strain associated with the transformation. Theoretically, accommodation may be achieved either by matrix plasticity or by inducing other transformation variants. This three-year GOALI proposal will develop new, fundamental insight into the pseudoelastic shape memory behavior of several Ni-Ti based alloys, including a ternary Ni-Cu-Ti, in collaboration with GM Research. The focus will be on alloys that undergo different martensite transformations and exhibit disparate functional fatigue properties. The approach is to meld innovative micron-scale mechanical tests and advanced microstructural characterization with analytic and novel microstructure-based modeling. Uniaxial deformation of focused-ion-beam-machined microcrystals will be used to probe the static and cyclic response as a function of matrix crystal orientation, and in order to directly measure the mechanical response (stress, strain, work output) for individual variants. Post-mortem characterization using transmission electron microscopy of the remnant substructure will be coupled with analytic modeling of the possible transformations. This approach will also yield directly the relative conditions for martensite transformation versus matrix plasticity over a range of component sizes. A new microstructure-based finite element approach will be developed that explicitly tracks local, discrete phase transformations coupled with rate-dependent crystal plasticity. For the first time, this will enable the treatment of size effects and the generation of local plasticity associated with transformations?a crucial step to understand and enhance pseudoelastic and shape memory response. The proposed effort integrates advanced characterization at The Ohio State University and the GM Research center with new experimental techniques at two DOE labs ? high temperature nanoindentation/pillar testing at Oak Ridge National Laboratory and in situ pillar testing at the National Center for Electron Microscopy.NON-TECHNICAL SUMMARY:Shape memory alloys (SMAs) are materials with remarkable properties that include the ability to bend and stretch to large extent under an applied load, then spring back to their original shape when the load is removed. In addition, SMAs can change shape when heated, after which they may either maintain their newly acquired shape or return to their original shape after cooling back down to room temperature. The automotive industry has recognized the phenomenal potential of SMAs since they are remarkably simple actuation devices compared with conventional motorized actuators. For instance, they could be used as small, ?solid-state? motors that could be used to reconfigure a wide range of components, greatly reducing the complexity of such systems. However, commercially available SMA materials are not presently operated at their full potential due to degradation in their shape-changing capabilities after experiencing many temperature or stress cycles (?functional fatigue?). This program is designed to develop a fundamental understanding of the materials science aspects associated with this degradation process, as well as the development of modeling capabilities to predict and improve the functional fatigue performance for automotive, medical and other applications. A vigorous program of interchange between OSU and GM will stimulate efficient transfer of knowledge and will provide ample mechanisms for experiencing both academic and industrial environments. In an exciting outreach effort, we will develop a high school inquiry-based teaching module about shape memory alloys and their applications. Several mechanisms insuring insertion of this module into local high schools have also been defined.