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

技术概述：形状记忆合金是一种具有显著性能的材料，它源于马氏体相变。形状记忆和伪弹性行为的一个基本方面还没有被很好地理解，那就是基质如何适应与变换相关的大应变。从理论上讲，调节可以通过基质的可塑性或通过诱导其他转换变体来实现。这项为期三年的目标计划将与GM Research合作，对几种镍-钛合金的伪弹性形状记忆行为产生新的、基本的见解，其中包括一种三元镍-铜-钛合金。重点将放在经历不同马氏体相变并表现出不同功能疲劳性能的合金上。其方法是将创新的微米级力学测试和先进的微结构表征与解析和新颖的基于微结构的建模相结合。聚焦离子束加工微晶体的单轴形变将被用来探测作为基质晶体取向的函数的静态和循环响应，以便直接测量单个变体的机械响应(应力、应变、功输出)。使用透射电子显微镜对残留物进行亚结构的尸检表征将与可能的转化的解析建模相结合。这种方法还可以在一定的成分尺寸范围内直接给出马氏体相变与母体塑性的相对条件。一种新的基于微观结构的有限元方法将被开发出来，它显式地跟踪局部的离散相变和速率相关的晶体塑性。这将首次使尺寸效应的处理和与转变相关的局部可塑性的产生成为可能--这是理解和增强伪弹性和形状记忆反应的关键一步。这项拟议的工作将俄亥俄州立大学和转基因研究中心的先进特征与能源部两个实验室的新实验技术结合在一起。橡树岭国家实验室的高温纳米压痕/柱子测试和国家电子显微镜中心的现场柱子测试。非技术摘要：形状记忆合金(SMA)是具有显著性能的材料，包括在施加载荷下能够大范围弯曲和拉伸，然后在载荷移除时弹回原始形状。此外，SMA在受热时可以改变形状，之后它们可以保持新获得的形状，或者在冷却到室温后恢复到原来的形状。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，SMA是非常简单的执行装置。例如，它们可以用作小型固态硬盘。可用于重新配置各种组件的电机，极大地降低了此类系统的复杂性。然而，商业上可用的形状记忆合金材料在经历了许多温度或应力循环(功能疲劳)后，由于其形状变化能力的退化，目前并不能充分发挥其潜力。该项目旨在加深对与该降解过程相关的材料科学方面的基本了解，以及开发用于预测和改善汽车、医疗和其他应用的功能疲劳性能的建模能力。俄亥俄州立大学和GM之间积极的交流计划将刺激知识的有效转移，并将提供充分的机制来体验学术和工业环境。在一项激动人心的外展工作中，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。还确定了确保将这一模块插入当地高中的几个机制。

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.