CAREER: Recrystallization in additive manufactured metallic materials

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

NON-TECHNICAL SUMMARY Near-net-shape, metal additive manufacturing (AM) (also known as 3D printing) may allow for a major paradigm shift in the automotive, aerospace and energy generation industries. The main challenge that remains for broad adoption of metal AM is the obtaining of comparable and consistent mechanical properties such as strength and ductility in all orientations regardless of print direction. This project explores the basic science of thermal treatments after printing to control the composition and arrangement of metals, at the atomic scale, to obtain uniform mechanical properties throughout a 3D printed part. Advanced high magnification imaging of defects that occur at an atomic level, called dislocations, is revealing how they organize themselves and what role they play in encouraging or discouraging the formation of inner structures in metals known as “grains”. These inner structures fundamentally dictate a metal’s performance and the process of creating smaller defect free grains is a process known as recrystallization. This research generates new perspectives on dislocations and recrystallization in AM to increase mechanical performance and enable longer lifespans during service. This research also intertwines with educational and outreach activities aiming to increase awareness of and participation in additive manufacturing among students. Activities include incorporation of AM within laboratory courses at the undergraduate and graduate levels, creation of a research center focused on AM at the University of Illinois, Urbana-Champaign, and continuous development of a free-to-participants, materials-themed summer camp for middle-school students targeting underrepresented minorities of low income. TECHNICAL SUMMARY Additive manufacturing (AM) enables near-net-shaping across a large variety of materials, thereby reducing the need for machining while also reducing waste. Unfortunately, this process generally induces strongly anisotropic properties which limit broad adoption as a manufacturing technique. Post-build annealing treatments aiming to trigger recrystallization are a simple and cost-efficient strategy to reduce property anisotropy in any geometry. Yet, despite a high dislocation density, most AM materials recrystallize surprisingly sparsely and with sluggish kinetics; an observation that still remains to be understood. The project is elucidating the fundamental mechanisms driving recrystallization in AM metallic materials fabricated by laser powder-bed fusion and directed energy deposition. An experimental-numerical correlative framework using electron microscopy combined with in-situ synchrotron experiments is being implemented to accurately map, digitize and analyze AM microstructures during recrystallization. Results are allowing for quantitative measurement of driving forces with a view to enable physics-based microstructure evolution laws tailored specifically to AM materials. With this approach, transformative printing and alloy design strategies for AM materials with isotropic properties are being produced. Research efforts are accompanied by outreach initiatives exposing students in central Illinois at the middle school, undergraduate, graduate and professional levels to the rapidly evolving field of AM. This project also enables the incorporation of metal AM into the undergraduate and graduate curriculum at the University of Illinois Urbana-Champaign. 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.