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

非技术描述：功能磁性材料可以具有优异的性能。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，并有可能取代目前需要几个移动部件的机械执行器，这些移动部件很难组装，而且很容易断裂。磁热材料具有一种特性，当暴露在磁场中时，它们可以冷却或加热，并且可以用作冷却设备，而不需要目前冰箱中所需的液体和压缩机。目前，制备功能磁性材料的复杂零件是很困难的。先进的激光或电子束制造技术提供了打印非常复杂的形状的能力，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的制造参数、成分、微结构和性能之间建立基本的理解，并使具有特定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与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。预计所获得的知识将减少功能磁性材料进一步采用的障碍，使其超越原型在许多领域和目前尚不能达到的应用领域，例如可打印的致动器、泵和固体冷却设备。结合功能材料、计算机建模和先进制造，将为K-12学生、他们的老师和家长创建基于经验的STEM外展活动。这些示范和动手实验将在当地学校、暑期学校和外联活动中进行，这些活动特别服务于经济困难和代表性不足的学生群体。在这种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的、多方面的和协作的工作环境的准备。这项研究的结果将发表在研究期刊和会议上，也可以通过博客文章、社交媒体和公开视频发表。技术说明：功能Heusler合金，如磁性形状记忆合金或磁热材料，在施加磁场时会产生高达10%的应变，并几乎与压电陶瓷一样快，或者实现固态冷却，效率比传统技术高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，这阻碍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、熔化和凝固而产生具有挑战性的微结构，并导致无功能或低功能部件。该奖项支持一项综合的实验和计算研究，旨在提高我们对在基于层状结构的先进制造和后处理中经历快速凝固和循环加热的Ni-Mn-Ga基Heusler合金的成分、微观结构和功能性能之间的基本了解。研究工作追求以下目标：(A)确定远非平衡快速凝固和循环加热条件下合金成分、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、微观偏析行为和磁性能的预测模型，以及(C)通过有针对性的快速凝固处理和后热处理，在功能Heusler合金的层状沉积中建立成分和晶粒度控制。这项研究的结果将使基于激光的Heusler合金沉积成为可能，并允许功能性、形状复杂的自限制动器组件(磁性形状记忆合金)和高效固态冷却设备(磁热材料)。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.