Collaborative Research: Enabling Magnetoplasticity in Polycrystalline Ni-Mn-Ga by Reducing Internal Constraints Through Porosity

合作研究：通过孔隙率减少内部约束，实现多晶 Ni-Mn-Ga 的磁塑性

• 批准号: 0805064
• 负责人: David Dunand
• 金额: $ 33万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-05-01 至 2013-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0805064&HistoricalAwards=false
• 关键词: Collaborative; Research; Enabling; Magnetoplasticity; Polycrystalline

TECHNICAL: 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 grains. The PIs recently discovered that porosity, because it reduces internal stresses, allows limited twinning to occur in polycrystalline Ni-Mn-Ga foams, resulting in magnetoplastic strains. Then, designing the foam architecture and grain microstructure will allow tuning continuously the magnetoplastic strain of these foams between those of a polycrystal (~0%) and a single crystal (~10%). In this basic study, PIs will develop a fundamental understanding of how foam architecture and grain microstructure enable magnetic-field-induced strains in polycrystalline magnetic shape-memory alloys, leading to experimentally-validated models that can quantitatively predict the magnitude of magnetoplastic strain for a given foam structure. To achieve this goal, fundamental experimental and theoretical studies of the mechanisms responsible for magnetoplasticity in the individual struts of foams will be carried out. The foam architecture will be varied, in terms of node and strut volume fraction as well as strut size and aspect ratio, by using two foam manufacturing methods (casting and powder metallurgy). The foam grain size and texture will be tailored: the ratio of grain to strut diameter will be varied from much smaller than unity (polycrystalline microstructure) to comparable to unity (bamboo microstructure), and the texture will be varied from random to strong fiber texture. Finally, the magneto-mechanical properties of the resulting foams will be characterized and numerically modeled on two length scales: at a shorter length scale, models based on dislocation-dislocation and dislocation-interface interactions will be developed to predict the effect of free surfaces on the constitutive behavior of Ni-Mn-Ga in small volumes; at larger length scale, finite-element models (FEM) will be created to predict, based on the constitutive behavior, the overall foam magneto-mechanical behavior. NON-TECHNICAL: The novel magnetic shape-memory foams, produced by the PIs in preliminary research, exhibit strains and response times comparable to Terfenol D, the best commercial magnetostrictive material, and are expected to show further improvements based on these fundamental study. As compared to Terfenol D, Ni-Mn-Ga foams have lower density and contain less expensive metals, and may thus grow rapidly in industrial importance, thus having a transformative effect on various sensor and actuator technologies. Also, while the present research will focus on Ni-Mn-Ga, the mechanisms studied are general in nature, and will thus apply to all other magnetic shape-memory alloys. Beyond sensor and actuator applications, the open foam porosity may enable new applications such as (i) micropumps without moving parts where fluids are displaced by magnetically deforming pores, or (ii) efficient magnetic cooling devices with high heat-transfer rates due to the large specific areas of foams. Finally, 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. The PIs have submitted a provisional patent and intend to pursue industrial applications which is key for transitioning the field to the US high-technology industry.

技术：磁场引起的双胞胎负责单晶Ni-Mn-GA中可以实现的高磁塑料菌株。相比之下，多晶Ni-Mn-GA没有磁性塑性性，因为双胞胎受到相邻晶粒之间产生的内部不兼容应力的抑制。 PIS最近发现，孔隙率降低了内部应力，因此在多晶Ni-Mn-GA泡沫中允许有限的双胞胎发生，从而导致磁性塑料菌株。然后，设计泡沫结构和谷物微观结构将允许在多晶（〜0％）和单个晶体（〜10％）之间连续调整这些泡沫的磁性塑料应变。在这项基础研究中，PIS将对泡沫结构和谷物微结构如何在多晶型磁性形状 - 内存合金中启用磁场诱导的菌株有基本的理解，从而导致实验验证的模型，从而可以定量地预测给定泡沫结构的磁性应变的幅度。为了实现这一目标，将对泡沫单个支撑磁性的机制进行基本实验和理论研究。通过使用两种泡沫制造方法（铸造和粉末冶金），就节点和支撑量分数以及支撑尺寸和纵横比而言，泡沫结构将变化。泡沫晶粒尺寸和纹理将被量身定制：晶粒与支撑直径的比率将从小于统一（多晶微观结构）到与统一（竹制微结构）相当的小得多，并且纹理将从随机的纤维质地变化。最后，将在两个长度尺度上对所得泡沫的磁力机械特性进行表征和数值模型：在较短的长度尺度上，基于脱位 - 脱位和脱位 - 接口相互作用的模型，以预测自由表面对小体积中Ni-Mn-GA组成型行为的影响；在较大长度的规模下，将创建有限元模型（FEM），以根据本构行为（总体泡沫磁力机械行为）预测。非技术：新型的磁性内存泡沫，由PI在初步研究中产生的新型磁性泡沫表现出与Terfenol D相当的菌株和响应时间，Terfenol D是最佳的商业磁性材料，并有望根据这些基本研究显示进一步的改进。与萜酚D相比，Ni-MN-GA泡沫的密度较低，含有较低的金属，因此可能在工业重要性上迅速增长，从而对各种传感器和执行器技术产生变革效应。同样，尽管本研究将集中在Ni-MN-GA上，但所研究的机制本质上是普遍的，因此将适用于所有其他磁性磁性合金。除了传感器和执行器应用之外，开放的泡沫孔隙率还可以实现新的应用，例如（i）微型泵，而没有运动部件，而动态孔被磁性变形孔置换，或者（ii）由于大型泡沫的大面积，具有高热量转移速率的有效磁性冷却设备。最后，该项目将教育两名研究生和几名本科生，他们的招聘将强调妇女和少数民族。除研究外，学生还将使用形状记忆材料参加各种外展活动，向年轻妇女，少数民族和小学（K-12）学生介绍材料科学和技术。 PI已提交临时专利，并打算从事工业应用，这是将该领域转移到美国高科技行业的关键。