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

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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.