8/8/2024 Jackson Brunner, Marie Charpagne
Written by Jackson Brunner, Marie Charpagne
Metal additive manufacturing (AM), also called 3D printing, is a disruptive processing method with enormous potential for the design of resilient structural materials with an extended lifetime. Amongst the alloys that are readily printable, stainless steels have been investigated the most. The superior mechanical properties of AM steels over their forged counterpart have now been extensively demonstrated.
However, the origins of their corrosion resistance remain under debate. Basic understanding of corrosion processes in those materials is critical to designing the next generation of printable alloys.
Evan DelVecchio, a recent master’s graduate of The Grainger College of Engineering’s Department of Materials Science and Engineering, recently led efforts to discover the microscale origins of corrosion damage in additive manufactured stainless steels. The research, published in Nature Publishing Journals’ Materials Degradation, reveals that cellular structures unique to metal additive manufacturing and inherited from out-of-equilibrium processing give these alloys their superior corrosion resistance.
Despite extensive literature on the topic, the actual physical processes governing corrosion resistance in those alloys are still under debate. Assistant Professor Marie Charpagne’s group tackled corrosion from a relatively different angle than usual. After printing 316L stainless steel in their laboratory, they employed 3D and correlative electron microscopy techniques to reveal the makeup of corrosion damage in these materials is determined by the underlying microstructure of the material. Specifically, cellular solidification structures resulting from rapid solidification produce a dense connected network at the micron scale, which delays chloride ions' attack and confers AM 316L with superior corrosion resistance. Such linkage is unique to AM steel and will likely translate to other 3D printed alloys.
This work made use of the Grainger Engineering Materials Research Laboratory shared facilities, including a focused ion beam for serial sectioning, along with transmission electron microscopy and atomic force microscopy for microstructure mapping. The Imaging Technology Group at the Beckman Institute assisted with graphics and visuals.
“I want to highlight Evan’s resilience in setting up corrosion experiments on his own, as they are challenging, and the results can be hard to interpret,” Charpagne said. “This is a great example of a successful MS project. He was assisted by Tiffany Liu, who has been conducting undergraduate research in my lab since its very beginning, and I have high hopes that she will continue this exciting line of research. We are also grateful for the precious guidance of Dr. Maryam Eslami, corrosion expert who recently joined the Grainger Engineering Applied Research Institute.
Other students involved in the research include Yen-Ting Chang and Jackson Nie, who are part of the Charpagne research team.
“I am grateful for the opportunity to be involved in the project as well as the research group as a whole,” said DelVecchio. “I feel my experience with the team has reflected the true value of research to me personally, in a way that exceeds purely academic expectations."
This work is part of a series of articles by the Charpagne group on process-microstructure-properties linkages in AM stainless steels, including grain boundary engineering, micro-mechanical behavior from room temperature down to cryogenic temperature for hydrogen applications, corrosion and surface functionalization.
This research is supported by the National Science Foundation and the Energy and Biosciences Institute.