CAREER: Understanding Sensitization and Corrosion Mechanisms in Additively Manufactured Metals for Improved Surface Finish, Mechanical Properties and Corrosion Resistance

这项学院早期职业发展(Career)助学金专注于识别、量化和利用粉末床熔融添加剂制造所生产的金属和合金中的敏化和腐蚀机制。敏化是指金属合金中的碳化物在晶界析出，导致合金容易发生晶间腐蚀。金属添加剂制造或三维打印使公司能够制造性能更好、生产时间更短的复杂部件。为了降低添加剂制造成本并扩大设计自由度，该项目建立了必要的理解，以利用腐蚀现象来创建可扩展且均匀的蚀刻工艺，从而在改善表面光洁度的同时溶解支撑物和捕获的粉末。具体地说，本研究项目建立了这些材料的印刷微结构、敏化动力学和腐蚀机理之间的基本关系。这一新的理解使制造商能够在改善表面光洁度和机械性能的同时控制材料的去除量。通过用简单的化学溶解来移除支撑结构来取代昂贵的后处理加工操作，这种新方法降低了制造成本，并为美国制造业提供了竞争优势。该奖项的STEM教育部分包括课程开发和与服务于代表性不足的少数族裔和残疾学生的团体的K-12外联伙伴关系。这项研究的具体目标是了解粉末床熔融处理的金属和合金的微观结构如何控制敏化动力学和腐蚀机理。为了实现这一认识，本项目的研究目标是：(1)了解敏化过程中的微观组织演变；(2)了解敏化微结构如何随深度变化而改变腐蚀行为和相关的自终止腐蚀停止机制；以及(3)量化敏化和溶解对机械性能和腐蚀性能的影响。为了实现这些研究目标，本项目以不锈钢、镍基高温合金和钛合金为模型系统，探索碳基增感和硫化敏化，以检验以下假设：(I)碳基敏化深度随着钝化元素扩散路径的增加而减少；(Ii)脱合金化随着扩散路径的减少而增加；以及(Iii)铬的耗尽区随着敏化速度的增加而减少得更快。主要的重点是更好地了解高温腐蚀环境中微观组织演变的动力学，以及增加对水环境中敏化金属的微结构相关腐蚀机理的理解。这一新知识被用于指导粉末床熔合金属零件的设计和制造，从而有效地去除支撑结构，改善表面光洁度，并提高断裂和抗疲劳性能。该项目允许PI推进材料科学、腐蚀和机械行为方面的知识基础，同时支持先进制造的职业生涯。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。

This Faculty Early Career Development (CAREER) grant focuses on identifying, quantifying, and exploiting sensitization and corrosion mechanisms in metals and alloys produced using powder-bed fusion additive manufacturing. Sensitization refers to the precipitation of carbides at grain boundaries in a metal alloy, causing the alloy to be susceptible to intergranular corrosion. Metal additive manufacturing or three-dimensional printing allows companies to manufacture complex parts with improved performance and shorter production times. To reduce the costs of additive manufacturing and expand design freedom, this project establishes the understanding necessary to exploit corrosion phenomena to create a scalable and uniform etching process to dissolve supports and trapped powder while improving surface finish. Specifically, this research project establishes the fundamental relationships between the as-printed microstructure, sensitization kinetics and corrosion mechanisms in these materials. This new understanding allows manufacturers to control the amount of material removed while improving surface finish and mechanical properties. By replacing expensive post-process machining operations with simple chemical dissolution to remove support structures, this new approach reduces manufacturing costs and provides U.S. manufacturing with a competitive advantage. The award’s STEM educational components include curriculum development and K-12 outreach partnerships with groups serving underrepresented minorities and students with disabilities.The specific goal of this research is to understand how the microstructure of powder-bed fusion-processed metals and alloys control sensitization kinetics and corrosion mechanisms. To achieve this understanding, the research objectives of this project are to: (1) understand microstructure evolution during sensitization; (2) understand how the depth-dependent sensitized microstructure changes the corrosion behavior and associated self-terminating etch-stop mechanism; and (3) quantify the impacts that sensitization and dissolution have on mechanical properties and corrosion performance. To achieve these research objectives, this project explores carburization and sulfidation-based sensitization of stainless steel, nickel-based superalloys, and titanium alloys as model systems to test the following hypotheses: (i) carbon-based sensitization depth decreases as the diffusion path for passivating elements increases; (ii) dealloying increases with decreasing diffusion path; and (iii) chromium depletion zone decreases faster with increasing sensitization rate. The overarching focus is to obtain a better understanding of the kinetics of microstructure evolution in high temperature corrosive environments along with increased understanding of the microstructure-dependent corrosion mechanisms in sensitized metals in aqueous environments. This new knowledge is used to guide the design and manufacturing of powder-bed fusion metallic parts towards efficient support structure removal, improved surface finish and increased fracture and fatigue resistance. This project allows the PI to advance the knowledge base in materials science, corrosion, and mechanical behavior while supporting a career in advanced manufacturing.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.