SusChEM-Collaborative Research: The Role of Surface Energy on Texture Development in Rare-Earth-Free Auxetic and Magnetostrictive Materials

技术总结在该项目中，PI推进了对导致晶界迁移率差异、织构发展和多晶金属中具有优选织构/晶粒取向的晶粒异常生长的机制的理解。他们将利用这种理解来开发低成本但高性能的多晶拉胀和/或磁致伸缩材料，这些材料是单晶状的。他们的研究方法将结合联合收割机多尺度计算模拟，理论模型和协同集成的见解，从定量实验研究中获得的再结晶，晶粒生长和织构发展的铁镓（Galfenol）和铁铝（Alfenol）为基础的二元和三元合金轧制板材。实验将被用来探索退火协议和表面能，晶粒流动性和纹理发展之间的关系。他们的假设是，表面能差异是选择性地形成类似单晶的晶粒结构和纹理的能力的主要驱动力。这一假设将通过建立晶粒生长和织构发展的热力学模型来研究。与此同时，基于第一原理的计算模拟和实验研究的Galfenol和Alfenol将进行，以帮助模型的制定和验证，并确定二元和三元铁合金的性能，应赋予高的拉胀性和/或磁致伸缩的材料，表面能可以用来促进各向异性的发展。这项研究与SusChEM倡议一致，通过开发用于处理磁致伸缩合金的方法，该方法允许使用地球丰富的、廉价的和良性的化学品，例如Al、Co、Ga、Mn和Sn，作为昂贵的关键材料的替代品，稀土元素例如Tb和Dy，其占~ 33 at.%的Terfenol-D。PI将引入一种方法，通过跟踪已知取向的颗粒表面上的液体镓液滴的接触角来确定具有特定晶体取向的金属颗粒的表面能。该方法克服了现有方法的缺点，例如水滴法，其适用于具有低表面能的玻璃和聚合物表面，以及高温破坏性和/或基于蠕变的方法，其适用于无定形固体和各向同性是合理近似的样品（例如高度多颗粒的样品）。这项研究将导致实现低成本多晶合金中昂贵的单晶合金的性能所需的理解。原子结构模型和晶体生长过程的基于能量的模型将用于深入了解如何控制和靶向所需晶体的选择性生长，以牺牲具有不太有利的机械和/或磁致伸缩特性的晶体为代价。铁铝和铁镓合金是该项目的重点之一，因为初步结果表明它们是工业和国防应用中使用的磁致伸缩合金的可持续替代品的良好候选者，这些合金含有稀土元素，如铽和镝。这项研究与可持续材料开发方面的进步需求保持一致，因为它专注于处理磁致伸缩合金的方法，这些方法允许地球丰富，廉价和良性的化学品被用作昂贵的关键材料的替代品，稀土元素在地壳中的成本显着更高，含量显着更少。待研究的铁铝合金和铁镓合金具有高度拉胀性，这种机械性能通常存在于聚合物中，但很少存在于金属中。存在结构拉胀合金的高工业影响的可能性，因为非结构拉胀（即聚合物）的研究表明，拉胀性可用于增强抗断裂和抗压痕性。该研究项目还将支持对博士后，研究生和本科生进行建模和处理各向异性，无稀土，单晶状材料的培训，以及开发测量各向异性固体表面能的新方法。学生将在期刊出版物，会议论文和演讲中传播研究成果。该小组将在该项目下指导代表性不足的（少数民族和妇女）高中、本科和研究生。PI将继续与K-12学生进行持续的外联活动。

TECHNICAL SUMMARYIn this project, the PIs advance understanding of the mechanisms that lead to grain-boundary mobility differences, texture development and abnormal growth of grains with a preferred texture/grain orientation in polycrystalline metals. They will use this understanding to develop low cost yet high-performance polycrystalline auxetic and/or magnetostrictive materials that are single-crystal-like. Their approach for this research will combine multiple-scale computational simulations, theoretical models and synergistically integrated insights gained from quantitative experimental studies of recrystallization, grain growth and texture development in rolled sheets of Fe-Ga (Galfenol) and Fe-Al (Alfenol) based binary and ternary alloys. Experiments will be used to explore relationships between anneal protocols and surface energy, grain mobility and texture development. Their hypothesis is that surface energy differences are the dominant driving force underlying the ability to selectively develop a grain structure and texture that is single-crystal-like. This hypothesis will be investigated by creating thermodynamic models of grain growth and texture development. In parallel, first-principle-based computational simulations and experimental studies of Galfenol and Alfenol will be conducted to aid in model formulation and validation, and to identify binary and ternary iron alloys with properties that should impart high auxeticity and/or magnetostriction in materials for which surface energy can be used to promote anisotropy development. This research is aligned with the SusChEM initiative through developing methods for processing magnetostrictive alloys that allow earth-abundant, inexpensive and benign chemicals, e.g. Al, Co, Ga, Mn and Sn, to be used as a replacement for expensive critical materials, the rare-earth elements such as Tb and Dy that comprise ~33at.% of Terfenol-D. The PIs will introduce a method for determining the surface energy of metal grains with a specific crystallographic orientation by tracking the contact angle of a drop of liquid gallium on grain surfaces of known orientation. This method overcomes shortcomings of existing methods, such as water-drop methods, that work for glass and polymeric surfaces with low surface energy and high-temperature destructive and/or creep-based methods that work for amorphous solids and samples for which isotropy is a reasonable approximation (e.g. highly polygranular samples).NON-TECHNICAL SUMMARY: This research will lead to the understanding needed to achieve the performance capabilities of costly single-crystal alloys in low-cost polycrystalline alloys. Models of atomic structure and energy-based models of crystal growth processes will be used to gain insights into how to control and target the selective growth of desired crystals at the expense of crystals with less favorable mechanical and/or magnetostrictive properties. The iron-aluminum and iron-gallium alloys that are one focus of this project have been targeted because of preliminary results that suggest they are good candidates for a sustainable alternative to magnetostrictive alloys used in industrial and defense applications that contain rare-earth elements like Terbium and Dysprosium. This research aligns well with the need for advances in the development of sustainable materials, as it focuses on methods for processing magnetostrictive alloys that allow earth-abundant, inexpensive and benign chemicals to be used as a replacement for expensive critical materials, the rare-earth elements that are both significantly more costly and significantly less abundant in the Earth's crust. The iron-aluminum and iron-gallium alloys to be studied are highly-auxetic, a mechanical property that is generally found in polymers but rarely in metals. The potential for high industrial impact of a structural auxetic alloy exists, as studies of non-structural auxetics (i.e. polymers) indicate that auxeticity can be used to enhance resistance to fracture and indentation. This research project will also support the training of postdoctoral, graduate and undergraduate students in modeling and processing anisotropic, rare-earth-free, single-crystal-like materials as well as in developing a new method for the measurement of surface energies of anisotropic solids. Students will disseminate research results in journal publications, conference papers and presentations. The team will mentor underrepresented (minority and women) high-school, undergraduate and graduate students under this project. The PIs will both continue to engage in on-going outreach to K-12 students.