Collaborative Research: Size Effects on Magneto-Mechanics of Ni-Mn-Ga Fibers

合作研究：Ni-Mn-Ga 纤维磁力学的尺寸效应

• 批准号: 1207282
• 负责人: David Dunand
• 金额: $ 34.71万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1207282&HistoricalAwards=false
• 关键词: Collaborative; Research; Size; Effects; Magneto

TECHNICAL SUMMARY:This project lays the foundation for a new class of active materials - magnetic shape-memory fibers with tailored geometry, microstructure and magneto-mechanical properties - to be used as transducers for micro-devices and as building blocks for composites or cellular structures. Magnetic-field-induced twinning is responsible for the high magnetoplastic strains achievable in monocrystalline Ni-Mn-Ga. By contrast, polycrystalline Ni-Mn-Ga shows no magnetoplasticity because twinning is inhibited by internal incompatibility stresses developed between adjacent, misoriented grains. The PIs recently discovered that porosity, because it reduces internal stresses, allows twinning to occur in polycrystalline Ni-Mn-Ga foams, resulting in magnetoplastic strains in the foam struts. Applying this concept to individual fibers, our hypothesis is that tailored grain size (with respect to fiber size) and grain orientations will allow tuning the magnetoplastic strain from polycrystalline (0%) to monocrystalline (~10%) behavior.In this basic study, we will develop a fundamental understanding of how fiber geometry and grain microstructure enable magnetic-field-induced strains in polycrystalline Ni-Mn-Ga fibers, leading to experimentally-validated models that can quantitatively predict the magnitude of magnetoplastic strain for a given fiber structure. Fundamental experimental and theoretical studies probing the mechanisms responsible for magnetoplasticity in the fibers will be carried out. First, the fiber geometry will be varied, in terms of cross-sectional shape and diameter, by using two versatile manufacturing methods (Taylor wire drawing and melt extraction). Then, the fiber grain size and texture will be tailored: the ratio of grain to fiber diameter will be varied from 1 (polycrystalline fiber) to ~1 (bamboo structure) and compared to single-crystal fibers; grain orientation will be varied from random to fiber texture. Third, the magneto-mechanical properties of the fibers will be characterized and numerically modeled on two length scales: (i) at a shorter length scale, models based on the mutual interaction of twinning dislocations and dislocation-interface interactions will predict the effect of free surfaces on the constitutive behavior of Ni-Mn-Ga in small volumes; (ii) at larger length scale, finite-element models will predict, based on the constitutive behavior, the magneto-mechanical behavior of an assembly of bamboo grains within a fiber. Collaborators will embed fibers in polymer matrix to create composites to study their magneto-mechanical properties, or create fiber bundles to study their magneto-caloric properties.NON-TECHNICAL SUMMARY:The present project is a coupled experimental-theoretical study of the magneto-mechanics of magnetic shape-memory fibers, a novel class of materials. It focuses on identifying, quantifying and predicting the effects of fiber geometry and grain microstructure upon reduction of internal stresses and the resulting enhancement in magnetoplastic strain, a phenomenon recently demonstrated in struts of foams by the PIs. The results obtained will be general in nature and thus applicable not only to Ni-Mn-Ga but also to the whole class of magnetic shape-memory alloys.Ni-Mn-Ga fibers with tailored grain structures are expected to show large magnetoplastic strain (i.e. they deform when exposed to a variable magnetic field) which are much higher than magnetostrictive material containing strategic rare-earth elements. These Ni-Mn-Ga fibers may be implemented without further processing in smart actuators and may thus grow rapidly in industrial importance, resulting in a transformative effect on various sensor and actuator technologies including bio-medical pumps, ink-jet printer valves, power-generation transducers, and haptics devices. Beyond sensor and actuator applications, fibers and fiber constructs may enable new applications such as efficient magnetic cooling devices with high heat-transfer rates due to their large specific areas. This project will educate two graduate students and several undergraduate students, whose recruitment will emphasize women and minorities. Beside research, the students will participate in various outreach activities using the shape-memory materials to introduce materials science and technology to young women, minorities, and grade school (K-12) students. This project will leverage collaboration with four international partners (in Europe and Asia) thereby generating high visibility and impact. The recent results of the PIs resonated strongly with the scientific community and were highlighted in national media. These contacts will be leveraged for disseminating results of the proposed project. The PIs have submitted two patents and pursue a spin-off project for transitioning the field to the US high-technology industry.

技术摘要：该项目为新型活性材料（具有定制几何形状、微观结构和磁机械特性的磁性形状记忆纤维）奠定了基础，可用作微型设备的传感器以及复合材料或蜂窝结构的构建块。磁场诱导孪晶是单晶 Ni-Mn-Ga 中可实现高磁塑性应变的原因。相比之下，多晶 Ni-Mn-Ga 不表现出磁塑性，因为孪生受到相邻、取向错误的晶粒之间产生的内部不相容应力的抑制。 PI 最近发现，由于孔隙率降低了内应力，因此多晶 Ni-Mn-Ga 泡沫中会出现孪晶，从而导致泡沫支柱中产生磁塑性应变。将这一概念应用于单根纤维，我们的假设是定制晶粒尺寸（相对于纤维尺寸）和晶粒取向将允许将磁塑性应变从多晶（0％）调整到单晶（〜10％）行为。在这项基础研究中，我们将对纤维几何形状和晶粒微观结构如何在多晶 Ni-Mn-Ga 纤维中产生磁场感应应变有一个基本的了解，从而建立经过实验验证的模型，可以定量预测给定纤维结构的磁塑性应变大小。 将进行基础实验和理论研究，探讨纤维磁塑性的机制。 首先，通过使用两种通用的制造方法（泰勒拉丝和熔体提取），纤维的几何形状将在横截面形状和直径方面发生变化。 然后，纤维晶粒尺寸和纹理将被定制：与单晶纤维相比，晶粒与纤维直径的比率将从1（多晶纤维）到~1（竹结构）变化；晶粒方向会从随机纹理到纤维纹理有所不同。第三，纤维的磁机械特性将在两个长度尺度上进行表征和数值模拟：（i）在较短的长度尺度上，基于孪生位错和位错界面相互作用的相互作用的模型将预测自由的影响表面对小体积 Ni-Mn-Ga 本构行为的影响； (ii) 在更大的长度尺度上，有限元模型将根据本构行为预测纤维内竹粒组件的磁机械行为。 合作者将纤维嵌入聚合物基体中以创建复合材料以研究其磁机械性能，或创建纤维束以研究其磁热性能。非技术摘要：本项目是磁机械的耦合实验理论研究磁性形状记忆纤维是一类新型材料。 它的重点是识别、量化和预测纤维几何形状和晶粒微观结构对减少内应力以及由此产生的磁塑性应变增强的影响，这是PI最近在泡沫支柱中证明的一种现象。所获得的结果在本质上是通用的，因此不仅适用于 Ni-Mn-Ga，而且适用于整个类别的磁性形状记忆合金。具有定制晶粒结构的 Ni-Mn-Ga 纤维预计会表现出大的磁塑性应变（即它们在暴露于可变磁场时会变形），该磁场比含有战略稀土元素的磁致伸缩材料高得多。 这些 Ni-Mn-Ga 纤维无需在智能执行器中进行进一步处理即可实现，因此在工业重要性方面可能会迅速增长，从而对各种传感器和执行器技术产生变革性影响，包括生物医学泵、喷墨打印机阀、电源一代传感器和触觉设备。除了传感器和执行器应用之外，纤维和纤维结构还可以实现新的应用，例如由于其较大的特定面积而具有高传热率的高效磁冷却装置。 该项目将培养两名研究生和几名本科生，其招生重点是女性和少数族裔。除了研究之外，学生们还将参加各种利用形状记忆材料的外展活动，向年轻女性、少数民族和小学（K-12）学生介绍材料科学和技术。该项目将利用与四个国际合作伙伴（欧洲和亚洲）的合作，从而产生较高的知名度和影响力。 PI 的最新结果引起了科学界的强烈反响，并在国家媒体上得到了重点报道。这些联系将用于传播拟议项目的结果。 PI 已提交两项专利，并正在开展一个衍生项目，将该领域转移到美国高科技产业。