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

在美国，超过55%的能源消耗是以废热的形式释放的。仅就制造业而言，每年未回收的废热总量估计为2500万亿BTU。美国汽车产生的废热相当于每年损失超过500亿美元。在各种余热回收技术中，固态热电机组是提高能源效率、缓解大气污染、减少碳排放的一种很有前途的策略。传统的三甘醇制造包括材料合成、组件组装和器件集成，生产率低、成本高。只有解决TEG制造中的以下关键挑战，才能在现有能源系统中实现TEG的广泛部署：以成本效益的方式合成丰富、低成本、可靠和高ZT(品质因数)的热电材料；TEG设备的可扩展制造；在温度梯度环境中实现功能分级。该项目有一个基于添加制造(AM)的净形状纳米制造工艺，该工艺利用材料科学、传热学和制造方面的最新进展来应对这些挑战。为了实现这一雄心勃勃的目标，弗吉尼亚理工大学、卡内基梅隆大学和华盛顿大学与AM的一位行业领导者合作，组建了一支由能源采集、材料科学家、热传递和制造组成的跨学科团队来自不同背景的学生将被培养成21世纪的劳动力。此外，我们亦会为K12学童的外展工作作出很大努力。本项目的目标是开发一种基于选择性激光熔化(SLM)的AM方法，用于高性能热电材料和功能器件的新型集成纳米制造工艺。此外，还将建立激光加工变量与热电材料特性之间的关联，以提供对激光与材料相互作用的基本了解，从而实现用于热电设备的净形状和可扩展的AM方法。具体来说，将检验以下假设：(1)激光AM过程中产生的非平衡条件会引入大量的纳米缺陷、纳米颗粒和丰富的多尺度晶界，这些缺陷会因声子散射而显著降低导热系数。(2)在纳米材料制备过程中加入掺杂的硅或其他纳米颗粒，可以改善材料的力学性能，提高材料的导电性，提高塞贝克系数。(3)基于激光的AM可以很容易地实现温差热电元件的梯度掺杂和沿长度方向的变截面积，从而最大限度地利用材料的温变特性，实现高性能的热电器件。(4)利用基于激光的AM，直接制造热电材料、绝热层、导电层和热交换器作为一个功能完整的能量收集系统，与传统的制造方法相比，可以产生更高的机械稳定性和热可靠性。这项技术以低成本、高效率和行业可扩展的清洁能源系统纳米制造为特征，如果成功测试和验证，将对汽车、发电站、钢铁厂等许多与能源和制造系统相关的行业具有极大的吸引力。了解热电材料电子和声子传输的基本原理，开发下一代制造工具，设计新的热传递系统，将提高能源系统的效率，减少美国对外国能源的依赖。工业伙伴关系加速了基础科学研究融入工业实践。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.