CAREER: Understanding and controlling the sintering of metal powders with nanoscale additives

University Of Tulsa, Tulsa OK

Investigators

Abstract

NON-TECHNICAL SUMMARY This CAREER project connects research on sustainable 3D printing of metals with education efforts to inspire K-12 and college students through hands-on materials science combined with inspiring stories about several highly accomplished scientists. The research addresses critical questions surrounding a type of metal 3D printing called binder jet. Metals are central to food, water, transportation, and healthcare, but unfortunately, metal extraction and production generates 10% of global climate change impacts. Therefore, there is a need for doing more with less for metals. Towards this, binder jet is one of the most promising ways to make sustainable metal parts at a large scale. However, binder jet is being held back by knowledge gaps about the science of sintering. Sintering happens when solid pieces of material fuse together over time, such as ice cubes sticking together in a freezer. For binder jet, sintering is critical because it fuses metal powders into the final part. Sintering is highly sensitive to the chemical composition of surfaces, yet there is little understanding about how small changes in surface compositions (such as coatings) influence the sintering of metal powders. To advance binder jet, this work uses a multi-modal approach to understand important physical and chemical processes during sintering. Overall, this research paves the way towards understanding, predicting, and controlling sintering of metals with trace additives, towards sustainable metal manufacturing. The project's integrated research and education efforts have broad impacts around society. The research itself opens new doors for scalable, sustainable metal manufacturing for automotive, aerospace, and beyond. Additionally, this project launches education initiatives that work towards full participation of people from all backgrounds, along with enhanced STEM education and educator development. These efforts start locally in the Tulsa community by sharing hands-on K-12 modules on sintering, along with captivating stories about highly accomplished scientists. The efforts expand globally in collaboration with TeachEngineering.org and NSBE. Overall, the integrated research and education supports the growth of a globally competitive STEM workforce. TECHNICAL SUMMARY The research of this project focuses on unlocking new paradigms for the performance and predictability of high-volume, high-efficiency metal parts fabricated by binder jet. The intellectual merit centers on establishing extensive process-structure-property relationships for sintered Al- and Ti-alloy powders with and without trace additives that enhance sintering. In detail, the investigation probes the evolution of particle interfaces, necks, grains, and pores during sintering with nanoscale additives (e.g., enhancing binders, nanoparticles, powder coatings, and infiltrants). The work uses in situ microscopy and spectroscopy to unravel coupled physical and chemical mechanisms, in light of bulk dilatometry, in situ quantification of sintering distortions, and mechanical properties after sintering. Additionally, this work studies important pore/grain-boundary interactions by introducing a new class of nanoscale infiltration, which provides a toolbox to study vacancy diffusion and pore/grain boundary interactions, as well as a new pathway for increasing the density of sintered metals. This work also quantifies part distortion via digital image correlation to calibrate models of binder jet sintering based on the material point method, a powerful way to model the physics of millions of particles. Overall, the research addresses key questions about the combined chemical/physical interactions of additives with the base metal during sintering. This opens new horizons for tailored/designer powders, nanoparticles, coatings, additives, and infiltrants. The research integrates closely with education that seeks to enrich science learning and inspire future STEM leaders. In collaboration with STEM educators in the Tulsa community, the work shares hands-on activities that bring sintering to life for students. Coupled with this hands-on learning is the sharing of stories, posters, and digital media about numerous highly accomplished engineers and material scientists. In collaboration with NSBE, these stories are distributed worldwide. Finally, building from the sintering research, a new laboratory module on powder metallurgy is added to the undergraduate curriculum at The University of Tulsa. 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.