CAREER: Unraveling Fundamental Mechanisms Governing Grain Refinement in Complex Concentrated Alloys Made by Additive Manufacturing Towards Strong and Ductile Structures

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The ability to produce strong yet tough structural alloys has been a quest to fully exploit the integrated innovation of materials and manufacturing. One longstanding challenge is the well-known strength-ductility trade-off; the stronger a given material is, the less ductile it becomes. Grain structure refinements have been studied for conventional alloys to enhance both the strength and ductility. To date, however, it remains unclear how grain refinements may be effectively applied to complex concentrated alloys (CCAs), which are compositionally compound with multiple principal chemical elements, made by additive manufacturing. This Faculty Early Career Development (CAREER) award supports fundamental investigations into additive manufacturing of CCAs. The project will perform different studies to test a hypothesis that increasing the entropy (i.e., level of disorder) in an alloy system will retard grain coarsening and stabilize microstructures, and thus, achieve both great strengths and high ductility. The research findings will bridge the knowledge gaps of microstructure engineering in designs and additively manufacturing of CCAs for high temperature and other critical applications. In concert, the formulated outreach activities will advance the research and educations in training the next generation of researchers and STEM leaders in advanced manufacturing, specifically fostering inclusions of women and minorities in manufacturing and related fields.The overarching goal of this research is to understand the underlying mechanism of grain refinements in CCAs made by additive manufacturing through a mixture of dissimilar alloy powders and subsequent melting and solidifying. The project will investigate grain growth kinetics and phase stability in complex composition space, using an effective research toolkit comprised of machine-learning enhanced modeling, high-throughput fabrication experiments, as well as microstructural and material characterizations. This research will address knowledge needs related to microstructure engineering for the additive manufacturing of CCAs by exploring microstructure configurations generated from dissimilar alloy using powder-based additive manufacturing technologies (directed energy deposition and powder-bed fusion, both using a laser heat source) with following expected outcomes: (i) quantification of alloy entropy effects on process-structure-property relationships to reveal the fundamental mechanism to strengthen CCAs with refined grains or other means, (ii) microstructure formation in CCAs to understand the difference between complex concentrated vs. traditional alloys made by powder based additive manufacturing, and (iii) process-structure-property models to establish specifically for CCAs in the composition space between stainless steels and nickel-based superalloys.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.