Determining the Origin of the Highly Auxetic Behavior of Iron-Based Alloys

技术支持：这个变革性的实验/理论研究项目将调查铁镓（Fe-Ga）和铁铝（Fe-Al）合金的拉胀或负泊松比行为的起源，这些合金分别沿着[110]晶体取向测量到低至-0.78和-0.45的值。系统的实验制造和表征，沿着广泛的密度泛函和分子动力学模拟，将使我们能够预测和优化组合物，原子排列，制造条件和测试程序，合理控制泊松比和这些金属间合金的弹性常数。该研究的智力价值在于应用对弹性常数如何相互作用并产生拉胀性的理解，以及1）用于模拟定制成分的二元Fe-Ga和Fe-Al合金的先进计算和理论工具，和2）由于两种二元合金系统的延展性和相对简单性，这些实验非常适合于模型验证，并且也适合于提供实验结果，指导建模工作。成功的结果将是了解原子位置和原子间力联合收割机如何结合在一起，导致金属的这种不寻常的性质，这将有助于开发定制的合金性能特性。将研究具有不同成分和处理的单晶Fe-Ga和Fe-Al样品。PI将进行拉伸测试并测量其他物理特性（如磁化强度，磁各向异性和光谱），以便在受控温度，磁场，负载和应变率下与理论计算进行比较。密度泛函计算将进行调查的相图和不同的非金属分布模式的相稳定性，并直接确定弹性常数和泊松比。 这两个系统的比较研究允许披露的关键因素，管理的泊松比在金属间化合物合金。非技术性：该研究项目的成功也将在MEMS、形状记忆和能量转换等材料研究领域产生强大的商业影响。这两种合金都可以溅射和电沉积，并且通过负泊松比的成分控制来定制不寻常的结构响应的能力表明了用于工业和国防应用的新型MEMS器件的巨大潜力。教育影响将包括两名研究生的培训，他们将接触到理论和实验研究，虽然位于相对的海岸，但将密切合作，整合跨学科的研究进展。除了适当地参观对方的校园外，PI还计划在夏季学期访问艾姆斯实验室，我们的合作者将向学生展示他们正在研究的合金的生长和表征的基础知识。学生将接触现代理论和实验材料研究的几乎所有方面。此外，研究成果将大大丰富课程“计算方法在物理和化学”由共同首席研究员开发的课程，它非常适合在PI的实验室工作的定义明确的本科生研究经验。将进行几个本科项目，以补充研究生的研究。PI参与区域社区学院和高中的学生推广和招募，并通过NSF REU计划和NSF赞助的科学与工程研究实习（RISE）计划指导本科生研究项目，并通过或妇女在工程办公室。

TECHNICAL: This transformative experimental/theoretical research project will investigate the origin of the auxetic or negative Poisson's ratio behaviors of iron-gallium (Fe-Ga) and iron-aluminum (Fe-Al) alloys, which have been measured at values of as low as -0.78 and -0.45, respectively along a [110] crystallographic orientation. Systematic experimental fabrication and characterization, along with extensive density functional and molecular dynamics simulations will allow us to predict and optimize compositions, atomistic arrangements, fabrication conditions and test procedures for rational control of Poisson's ratio and the elastic constants of these intermetallic alloys. The intellectual merit of the research lies in applying the understanding of how elastic constants interact and produce auxeticity together with 1) advanced computational and theoretical tools for modeling binary Fe-Ga and Fe-Al alloys of tailored compositions, and 2) experiments that because of the ductility and relative simplicity of the two binary alloy systems are well suited for model validation and also for providing experimental results that can guide the modeling efforts. The outcome when successful will be learning how atomic placement and inter-atomic forces combine to result in this unusual property for a metal, an insight that will aid in developing tailored alloy performance characteristics. Single crystal Fe-Ga and Fe-Al samples with varying compositions and treatments will be studied. PIs will conduct tensile tests and measure other physical properties (such as magnetization, magnetic anisotropy, and optical spectra) for comparison with theoretical calculations under controlled temperature, magnetic field, load and strain rates. Density functional calculations will be performed to investigate the phase diagram and phase stability of different metalloid distribution patterns, and to directly determine elastic constants and Poisson's ratios. Comparative studies for these two systems allow disclosure of key factors that govern the Poisson's ratios in intermetallic alloys. NON-TECHNICAL: The success of this research project will also have a strong commercial impact in areas of materials research such as MEMS, shape memory and energy conversion. Both of these alloys can be sputtered and electrodeposited, and the ability to tailor unusual structural responses through compositional control of the negative Poisson's ratio suggests a huge potential for novel MEMs devices for industrial and defense applications. Educational impact will include training of two graduate students, who will be exposed to both theoretical and experimental research and who, although located on opposite coasts, will work closely on integrating research progress across disciplines. In addition to visiting each other's campus as appropriate, PIs have plans for both to visit Ames Lab during the summer term, where our collaborator will show the students the basics of growing and characterizing the alloys they are studying. Students will touch almost all the aspects of modern theoretical and experimental materials research. Additionally, research results will greatly enrich the curriculum of the course "Computational Approaches in Physics and Chemistry" developed by the co-Principal investigator, and it is ideally suited for well defined undergraduate research experiences working in the PI's lab. Several undergraduate projects will be undertaken to supplement the graduate student's research. The PI participates in outreach and recruiting of students at regional community colleges and high schools, and has extensive experience mentoring undergraduate student research projects through the NSF REU program and an NSF-sponsored Research Internship in Science and Engineering (RISE) Program run through or Women in Engineering Office.