CAREER: Understanding thermal phase change processes in metal additive manufacturing

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Laser-based additive manufacturing, including 3D metal printing, has revolutionized manufacturing processes by allowing manufacturers to make parts with complicated shapes that can be highly customized and making it possible to incorporate patterns of composition and micro-structure that may ultimately lead to new classes of materials and applications. Yet widespread implementation of additive manufacturing is limited by both technical issues, such as lack of quality control and part-to-part repeatability, and societal factors, such as the readiness of the engineering workforce. Mechanical properties, such as strength, hardness, and fatigue resistance – important quantities for any load-bearing component - are dictated by the material microstructure. These material properties are, in turn, governed by the details of the process: laser characteristics, the behavior of melted material, solidification, and the temperature of the workpiece over time. The opacity of metal has previously limited the ability to study the behavior of the melted material and the mechanism of solidification. Through an innovative research and educational approach, this project addresses challenges in implementing additive manufacturing, both the technical aspects, including microstructure and defect control, and the workforce development, laying the foundation for the broad implementation of robust and reliable additive processes.The scientific focus of this interdisciplinary project is to provide a comprehensive understanding of the thermal processes governing powder melting, convective mixing, and solidification in laser-based additive manufacturing of compositionally graded metals. Ex-situ experiments using an optically transparent surrogate system enable the characterization of phase change and fluid mixing. Based on preliminary experiments, two scenarios will be highlighted: i) the influence of powder impact location on melting and mixing, and ii) melting, mixing, and solidification of dissimilar materials. Using a unique in-situ high-speed thermal infrared imaging setup, capable of capturing transient events within the melt pool at the millisecond time scale, solidification dynamics in the transition zone of two metals will be quantified. Correlation of ex-situ and in-situ measurements along with post-deposition material characterization has the potential to lead to transformative advancements in additive manufacturing by creating a fundamental framework to couple process parameters with microstructural and defect development. Leveraging the fascination of 3D printing, educational activities aim at broadening and deepening participation of young people in science and engineering. At the core of these activities is the development of a 3D chocolate printer, which integrates hands-on scientific learning experiences with the appeal of high-speed imaging with different learning modules for both K-12 and undergraduate students. A specific focus is on empowering middle-school aged girls to pursue careers in STEM by providing a fun and low-stake introduction to additive manufacturing and thermal-fluid sciences.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.