Collaborative Research: Net-Shape and Scalable Additive Manufacturing for Thermoelectric Waste Heat Recovery Materials and Devices using Selective Laser Melting

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Over 55 percent of the energy consumed in the US is released as waste heat. For the manufacturing sector alone, the total unrecovered waste heat is estimated to be 2,500 trillion BTU per year. The waste heat from American automobiles is equivalent to losing over $50 billion each year. Among various waste heat recovery technologies, solid-state thermoelectric generators (TEGs) are a promising strategy to increase energy efficiency, alleviate air pollution, and reduce carbon emissions. Traditional TEG manufacturing includes material synthesis, module assembly, and device integration, which has low productivity and high cost. A widespread deployment of TEGs in existing energy systems can be achieved only by resolving following key challenges in TEG manufacturing: cost-effective synthesis of abundant, low cost, reliable, and high ZT (figure of merit) thermoelectric materials; scalable manufacturing of TEG devices; function graded realization in the temperature gradient environment. This project has an additive manufacturing (AM) based net-shape nanomanufacturing process, that takes the advantages of the latest advances in materials science, heat transfer, and manufacturing, to tackle these challenges. To accomplish this ambitious goal, an interdisciplinary team of energy harvesting, material scientist, heat transfer and manufacturing is assembled at Virginia Tech, Carnegie Mellon, and UW, in collaboration with an industry leader of AM. Students from diverse background will be trained for the twenty-first century workforce. Great efforts will also be made for outreaches to K12 students. The objective of this project is to develop a novel integrated nanomanufacturing process for high-performance thermoelectric materials and functional devices using the selective laser melting (SLM) based AM method. Furthermore, a correlation between the laser processing variables and thermoelectric material characteristics will be established to provide fundamental understanding of laser-material interactions to achieve a net-shape and scalable AM method for thermoelectric devices. Specifically, the following hypotheses will be tested: (1) The non-equilibrium conditions produced during the laser-based AM process can introduce numerous nano-defects, nanoscale particles, and abundant multi-scale grain boundaries, which can reduce the thermal conductivity dramatically by phonon scatterings. (2) doped Si or other nano-particles will be used as additive materials in the nanomanufacturing process to improve the mechanical properties, enhance the electrical conductivity, and increase the Seebeck coefficient. (3) The laser-based AM can readily realize the graded doping and variable cross-section areas along the length of the thermoelectric elements with temperate variance to make the best use of the temperature-dependent material properties for achieving high performance thermoelectric devices. (4) Using the laser-based AM, the direct manufacturing of thermoelectric materials, thermal insulation layers, electrical conductor layers, and heat exchangers as a functional and integrated energy harvesting system, can result in higher mechanical stability and thermal reliability as compared to the traditional manufacturing approaches. Characterized as low-cost, high-efficiency, and industry-scalable nanomanufacturing of clean energy systems, this technology, if successfully tested and validated, will become extremely attractive for many industries associated with energy and manufacturing systems, such as automobiles, power stations, steel plants and many more. Understanding the fundamentals of electron and phonon transport for thermoelectric materials, developing next generation manufacturing tools, and designing novel heat transfer systems will result in increased efficiency of the energy system and reduced of US dependency on foreign energy sources. The industrial partnership accelerates the assimilation of basic science research into industrial practice.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.