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

这项教师早期职业发展（Career）资助的重点是识别、量化和开发使用粉末床熔融增材制造生产的金属和合金的敏化和腐蚀机制。敏化是指合金中碳化物在晶界处析出，使合金易受晶间腐蚀。金属增材制造或三维打印使公司能够制造具有更高性能和更短生产时间的复杂零件。为了降低增材制造的成本并扩大设计自由度，该项目建立了对利用腐蚀现象的必要理解，以创建可扩展且均匀的蚀刻工艺，以溶解支撑和捕获的粉末，同时改善表面光洁度。具体而言，本研究项目建立了这些材料的打印微观结构，敏化动力学和腐蚀机制之间的基本关系。这种新的认识使制造商能够控制去除的材料量，同时改善表面光洁度和机械性能。通过用简单的化学溶解去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，为美国制造业提供了竞争优势。该奖项的STEM教育组成部分包括课程开发和与少数族裔和残疾学生服务群体的K-12外展伙伴关系。本研究的具体目标是了解粉末床熔合加工金属和合金的微观结构如何控制敏化动力学和腐蚀机制。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结构演变；(2)了解深度相关的敏化微观结构如何改变腐蚀行为和相关的自终止腐蚀停止机制；(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，本项目探索了不锈钢、镍基高温合金和钛合金的渗碳和硫化物敏化作为模型系统，以测试以下假设：(i)碳基敏化深度随着钝化元素扩散路径的增加而降低；（ii）合金化程度随扩散路径的减小而增加；(3)随着敏化率的增加，铬损耗区减小得更快。首要的重点是更好地了解高温腐蚀环境中微观结构演变的动力学，以及对水环境中敏感金属的微观结构依赖腐蚀机制的进一步了解。这一新知识用于指导粉末床熔合金属部件的设计和制造，以实现有效的支撑结构去除，改善表面光洁度，提高断裂和抗疲劳性。该项目使PI能够提升材料科学，腐蚀和机械行为方面的知识基础，同时支持先进制造业的职业生涯。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.