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

非技术性总结这个职业项目将金属可持续3D打印的研究与教育工作联系起来，通过实践材料科学结合几个高成就黑人科学家的鼓舞人心的故事来激励K-12和大学生。这项研究解决了围绕一种名为粘合剂喷射的金属3D打印的关键问题。金属是食品、水、交通和医疗保健的核心，但不幸的是，金属开采和生产产生了10%的全球气候变化影响。因此，有必要用更少的金属做更多的事情。对此，粘结剂喷射是大规模制造可持续金属零件的最有前途的方法之一。然而，粘结剂喷射机受到烧结科学知识空白的阻碍。当固体材料随着时间的推移融化在一起时，就会发生烧结，比如冰块在冰箱里粘在一起。对于粘结剂喷射机，烧结是关键，因为它将金属粉末熔化成最终部件。烧结对表面的化学成分高度敏感，但对表面成分(如涂层)的微小变化如何影响金属粉末的烧结却知之甚少。为了推进粘结剂喷射，这项工作使用多模式方法来了解烧结过程中的重要物理和化学过程。总体而言，这项研究为了解、预测和控制使用微量添加剂的金属烧结，实现可持续的金属制造铺平了道路。该项目的综合研究和教育努力在社会上产生了广泛的影响。这项研究本身为汽车、航空航天和其他领域的可扩展、可持续金属制造打开了新的大门。此外，该项目发起了教育倡议，努力让历史上代表性不足的群体的人充分参与STEM，同时加强STEM教育和教育者发展。这些努力始于当地的塔尔萨社区，分享关于烧结的动手K-12模块，以及关于高度成就的黑人科学家的引人入胜的故事。这些努力通过与TeachEngineering ering.org和NSBE的合作在全球范围内扩展。总体而言，整合的研究和教育支持了一支多样化的、具有全球竞争力的STEM工作队伍的发展。技术总结本项目的研究重点是为粘结剂喷射制造的大容量、高效率金属部件的性能和可预测性提供新的范例。智慧的优点集中在建立广泛的工艺-结构-性能关系，包括添加和不添加促进烧结的微量添加剂的铝和钛合金粉末。详细地，研究了纳米级添加剂(例如，增强粘结剂、纳米颗粒、粉末涂料和渗透剂)在烧结过程中颗粒界面、颈部、颗粒和气孔的演变。这项工作使用原位显微镜和光谱学来揭示物理和化学耦合的机制，结合体积膨胀法、烧结变形的原位量化和烧结后的机械性能。此外，这项工作通过引入一类新的纳米渗透来研究重要的孔/晶界相互作用，这为研究空位扩散和孔/晶界相互作用提供了工具箱，并为提高烧结金属的密度提供了一条新的途径。这项工作还通过数字图像相关量化了部分变形，以物点法为基础校准粘结剂喷射烧结模型，这是模拟数百万粒子物理的一种强有力的方法。总体而言，这项研究解决了关于添加剂在烧结过程中与母材的化学/物理联合作用的关键问题。这为定制/设计粉末、纳米颗粒、涂料、添加剂和渗透剂开辟了新的领域。这项研究与寻求丰富科学学习和激励未来STEM领导者的教育紧密结合。与塔尔萨社区的STEM教育工作者合作，这项工作分享了将烧结带入学生生活的实践活动。与这种实践学习相伴随的是分享关于许多高度成就的黑人工程师和材料科学家的故事、海报和数字媒体。在与NSBE的合作下，这些故事在世界各地发行。最后，在烧结研究的基础上，在塔尔萨大学的本科课程中增加了一个新的粉末冶金实验室模块。该奖项反映了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。

NON-TECHNICAL SUMMARYThis 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 Black 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 historically underrepresented groups in STEM, 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 Black scientists. The efforts expand globally in collaboration with TeachEngineering.org and NSBE. Overall, the integrated research and education supports the growth of a diverse, globally competitive STEM workforce.TECHNICAL SUMMARYThe 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 Black 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.