Collaborative Research: Mechanisms of hierarchical microstructure formation under rapid solidification of functional Heusler alloys

非技术描述：功能磁性材料具有优异的性能。磁性形状记忆合金在磁场的作用下可以从一种形状转变为另一种形状，并且有可能取代目前需要几个难以组装且容易损坏的运动部件的机械致动器。磁致热材料具有一种特性，即当它们暴露在磁场中时可以冷却或加热，并且可以用作冷却装置，而不需要目前冰箱中需要的液体和压缩机。目前，功能磁性材料的复杂零件的制造是一个难点。先进的激光或电子束制造技术提供了打印非常复杂形状的能力，但会产生具有挑战性的微结构，从而导致非功能部件。该奖项支持的研究将在先进制造参数、成分、微观结构和性能之间建立基本的理解，并使具有目标功能或行为的磁性材料的先进制造成为可能。该方法采用了快速冷却和凝固处理和小规模实验的创新组合，具有广泛的计算建模，验证实验和表征。所获得的知识预计将减少在各种领域和目前遥不可及的应用中进一步采用功能磁性材料的障碍，例如可打印执行器，泵和固体冷却装置。功能材料、计算机建模和先进制造的结合将用于为K-12学生、他们的老师和家长创造基于体验的STEM推广活动。这些示范和实践实验将在当地学校、暑期学校和外展活动中进行，这些活动将特别为经济困难和代表性不足的学生群体提供服务。在这个多学科的研究环境中培养本科生和研究生将增强学生对快速变化，多方面和协作的工作场所的准备。这项研究的结果将在研究期刊和会议上发表，也可以通过博客文章、社交媒体和公开视频发表。技术描述：功能性Heusler合金，如磁性形状记忆合金或磁热材料，在外加磁场下产生高达10%的应变，并且几乎与压电陶瓷一样快，或者使固态冷却效率比传统技术提高30%。目前，具有良好功能性能的复杂形状零件的制造非常有限，影响了这些材料的广泛应用。先进的激光和电子束制造技术可以实现复杂的构建设计，但由于快速加热、熔化和凝固，导致微结构具有挑战性，并导致无功能或低功能部件。该奖项支持一项综合实验和计算研究，旨在提高我们对Ni-Mn-Ga基Heusler合金的成分、微观结构和功能特性的基本理解，这些合金在基于层的先进制造和后处理中经受快速凝固和循环加热。研究工作追求以下目标：(A)确定非平衡快速凝固和循环加热条件下合金成分、显微组织和性能之间的基本关系；(B)开发基于calphad的非平衡相形成、微偏析行为和磁性能的预测模型；(C)通过有针对性的快速凝固加工和后热处理，在功能Heusler合金层状沉积中建立成分和晶粒尺寸控制。这项研究的结果将使基于激光的Heusler合金沉积成为可能，并允许功能、形状复杂、自我限制的致动器组件（磁性形状记忆合金）和高效的固态冷却装置（磁热材料）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Description: Functional magnetic materials can have outstanding properties. Magnetic shape memory alloys change from one shape to another with the application of a magnetic field, and can potentially replace mechanical actuators that currently need several moving parts that are difficult to assemble and might break easily. Magnetocaloric materials have a characteristic that allows them to cool or heat when exposed to a magnetic field, and might be used as cooling devices without the need of liquids and compressors currently required in refrigerators. Presently, it is difficult to fabricate complex parts of functional magnetic materials. Advanced, laser or electron beam manufacturing techniques offer the ability to print very complex shapes, but create challenging microstructures that result in non-functional parts. This award supports research that will establish a fundamental understanding between advanced manufacturing parameters, composition, microstructure and properties, and enable advanced manufacturing of magnetic materials with a targeted set of functions, or behaviors. The approach employs an innovative combination of rapid cooling and solidification processing and small-scale experiments, with extensive computational modeling, and validation experiments and characterization. The gained knowledge is expected to reduce barriers for further adoption of functional magnetic materials beyond prototypes in a large variety of fields and currently out-of-reach applications, e.g. printable actuators, pumps and solid cooling devices. The combination of functional materials, computer modelling, and advanced manufacturing will be used to create experience-based STEM outreach activities for K-12 students, their teachers and parents. These demonstrations and hands-on experiments will take place at local schools, summer schools and outreach events which serve especially economically challenged and underrepresented students populations. The training of undergraduate and graduate students in this multidisciplinary research environment will enhance the students' preparedness for fast-changing, multifaceted and collaborative work place. The results of this research will be presented in research journals and conferences, but also through blog-posts, social media and openly accessible videos.Technical Description:Functional Heusler alloys such as magnetic shape-memory alloys or magnetocaloric materials induce up to 10% strain under an applied magnetic field and actuate nearly as fast as piezoceramics, or enable solid-state cooling with up to 30% better efficiency than traditional technologies. Presently, the fabrication of complex shaped parts with good functional properties is very limited, compromising a broad application of these materials. Advanced, laser and electron beam manufacturing techniques enable complex build design, but create challenging microstructures due to rapid heating, melting and solidification, and result in non-functional or low functionality parts. This award supports an integrated experimental and computational research that aims to improve our fundamental understanding between composition, microstructure and functional properties in Ni-Mn-Ga based Heusler alloys subjected to rapid solidification and cyclic heating in layer-based advanced manufacturing and post-processing. Research efforts pursue the following goals: (A) Identify fundamental relations between alloy composition, microstructure and properties under far-from-equilibrium rapid solidification and cyclic heating conditions, (B) develop CALPHAD-based predictive models for nonequilibrium phase formations, micro-segregation behavior and magnetic properties, and (C) establish composition and grain size control in layered deposits of functional Heusler alloys through targeted rapid solidification processing and post-heat treatment. The outcome of this research will enable laser-based deposition of Heusler alloys and permit functional, complex shaped, self-limiting actuator components (magnetic shape-memory alloys) and highly efficient solid-state cooling devices (magnetocaloric materials).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.