UVA Engineering Team Provides Unprecedented Insight into the Mechanisms of Corrosion in Wet and Dry Environmentsmkw3a@virginia.edu
Recent leaps in imaging technologies have given scientists new tools to understand and take advantage of phenomena that occur naturally when matter is organized at the nanoscale. Microscopy tools and techniques have opened new vistas in many fields including medicine, computing, chemical catalysis and materials synthesis.
Petra Reinke, professor of materials science and engineering at the University of Virginia School of Engineering, brings the power of these tools to bear on corrosion at the atomic scale, where properties change as a function of particle size.
Reinke and members of her nanomaterials and surface science research group help build comprehensive models to describe and predict corrosion and oxidation reaction down to the atomic scale, as members of the Understanding Corrosion in 4D multi-university research initiative led by Laurence Marks, professor of materials science and engineering at Northwestern University.
The MURI team measures and models how nanoscale structure influences material properties in 4D—the nano, micro and meso scale at which material behaviors are observed over time. The Office of Naval Research funds this initiative, which points to new materials that resist corrosion from saltwater.
“Metals and alloys are the building blocks from which we construct bridges, cars, ships and pipes to carry water, gas and oil. These materials are always susceptible to corrosion by oxygen, water and chloride, leading to critical loss of function and failure that incurs a significant economic and environmental burden,” Reinke said.
Preventing failure and enhancing longevity are the cornerstones of alloy design. To aid the design process, Reinke’s group starts with a pristine metal and measures how materials form oxide layers and thus protect themselves.
These processes are ubiquitous phenomena that initiate at the surface of a material. Reinke’s team homed in on the absorption behavior and growth of oxides, a critical step toward corrosion resistance.
Their key take-away? If you want to understand the early stages of oxidation, think locally, with a heterogeneous point of view.
“Looking at the growth of these partial oxide layers on the surface, we were surprised by how disparate they were,” said Will Blades, a December 2020 materials science and engineering Ph.D. graduate advised by Reinke. “Going from one 25 by 25 nanometer area to another, the surface looked wildly different. The layer was populated by a number of different oxides displaying a variety of structures.”
Reinke’s team focused on oxidation of nickel-chromium-based superalloys in wet and dry environments and what happens when a third element, such as molybdenum or tungsten, is added to the mix. The work on aqueous corrosion was pursued in collaboration with John R. Scully, Charles Henderson Chaired Professor of Materials Science and Engineering at UVA, whose research group has long-standing expertise in the field.
Reinke’s research yields unprecedented insight into the mechanisms of corrosion and oxidation reactions. Her research team discovered that adding only a small percentage of tungsten or molybdenum to the alloy, which has long been known to suppress alloy degradation, works by catalyzing the formation of chromia, a highly coveted passive layer—meaning it is does not react when exposed to other particles.
“Our research underscores the impact of the alloy surface and initial reaction steps on the functionality of the passive and oxide layer,” Reinke said. “The protective function of the surface layer is evident, for example, in its resistance to chloride attack, but only if surface reactions do not roughen up the oxide layer.”
“Initial oxidation behavior at the surface is sensitive to alloy composition, temperature, crystallographic orientation at the surface—there’s quite a lot left to understand,” Blades said. He will continue to follow these clues as a post-doc with Karl Sieradzki, professor of materials science and engineering at Arizona State University.
Blades will not have to trade the Blue Ridge for the Hayden Butte Reserve to pursue his post-doc, however. Sieradzki, Scully, and Elizabeth J. Opila, professor of materials science and engineering at UVA, are partners in a new multi-university research initiative led by Mitra Taheri, professor of materials science and engineering at Johns Hopkins University, to understand how a specific class of metal alloys, so-called high entropy alloys, behave in high-temperature and/or corrosive environments.
Blades will leverage his experience as a member of Sieradzki’s MURI team. Whereas Reinke’s MURI research was applied to alloys of two primary components, this new research initiative looks at alloys composed of five elements and how percentage changes of two or more alloys affect oxidation behavior.
“These are such great complementary pieces, enabling us to connect the dots from the early to later stages of oxidation, and from nanoscale to bulk materials,” Blades said.
Reinke recently earned funding from the National Science Foundation to conduct experiments to unravel the detailed mechanisms of the oxidation process, which takes the work started in the MURI project to the next level. Reinke seeks to jump-start the oxidation process in ways that ensure a stable, protective oxide layer, and to identify beneficial and replicable chemical mechanisms to improve corrosion resistance under challenging conditions. Reinke and Ashleigh Baber, associate professor of materials chemistry at James Madison University, are invested in getting students involved in surface science, and will integrate their teaching efforts within this NSF award.