Research Spending & Results

• Owen Hildreth
• (303) 384-2457
• ohildreth@mines.edu

• FY 2020=$515,000

• Khershed Cooper
• (703) 292-7017
• khcooper@nsf.gov

Awardee Location

Primary Place of Performance

Abstract at Time of Award

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.