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

在这个项目中，PIs促进了对多晶金属中导致晶界迁移率差异、织构发育和具有优选织构/晶粒取向的晶粒异常生长的机制的理解。他们将利用这一认识来开发低成本但高性能的单晶状多晶增减和/或磁致伸缩材料。他们的研究方法将结合多尺度计算模拟、理论模型和从Fe-Ga （Galfenol）和Fe-Al （Alfenol）基二元和三元合金轧制板的再结晶、晶粒生长和织构发展的定量实验研究中获得的协同集成见解。实验将用于探索退火协议与表面能、晶粒迁移率和织构发展之间的关系。他们的假设是，表面能的差异是选择性地形成单晶状晶粒结构和纹理的主要驱动力。这一假设将通过建立晶粒生长和织构发育的热力学模型来研究。同时，将进行基于第一性原理的Galfenol和Alfenol的计算模拟和实验研究，以帮助模型的制定和验证，并确定二元和三元铁合金的特性，这些特性应赋予材料的高互补性和/或磁致伸缩，表面能可用于促进各向异性的发展。这项研究与SusChEM计划一致，通过开发加工磁致伸缩合金的方法，使地球丰富，廉价和良性的化学物质，如Al， Co, Ga， Mn和Sn，可以用来替代昂贵的关键材料，稀土元素，如Tb和Dy，包含~33at。% Terfenol-D。pi将引入一种方法，通过跟踪液滴镓在已知取向的晶粒表面上的接触角，来确定具有特定晶体取向的金属晶粒的表面能。该方法克服了现有方法的缺点，例如适用于低表面能的玻璃和聚合物表面的水滴法，以及适用于各向同性合理近似的无定形固体和样品（例如高多颗粒样品）的高温破坏性和/或蠕变方法。非技术总结：这项研究将有助于理解在低成本多晶合金中实现高成本单晶合金的性能。原子结构模型和晶体生长过程的能量模型将用于深入了解如何控制和瞄准所需晶体的选择性生长，而牺牲不太有利的机械和/或磁致伸缩性能的晶体。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含有稀土元素（如铽和镝）的磁致伸缩合金的可持续替代品。这项研究与可持续材料发展的进步需求是一致的，因为它关注的是处理磁致伸缩合金的方法，这些方法允许地球上丰富的、廉价的、良性的化学物质被用作昂贵的关键材料的替代品，稀土元素在地壳中既昂贵又不丰富。要研究的铁铝合金和铁镓合金是高度auxetic的，这种机械特性通常存在于聚合物中，但很少存在于金属中。由于对非结构助塑剂（即聚合物）的研究表明，结构性助塑剂可以用来增强抗断裂和抗压痕，因此结构性助塑剂具有很高的工业影响潜力。该研究项目还将支持培养博士后、研究生和本科生，研究如何建模和处理各向异性、无稀土、单晶类材料，以及开发一种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。该团队将在该项目下指导代表性不足的高中生、本科生和研究生（少数民族和女性）。这两家pi将继续为K-12学生提供持续的服务。

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.