December 2006
Sieradzki and colleagues reveal advances in predicting corrosion of metal alloys
Many of the systems, structures, instruments and vehicles the world depends on to protect public health and safety are endangered by corrosion of metal alloys such as stainless steel.
The high degree of precision required in the operation of fossil fuel and nuclear power plants, pipelines, aircraft and medical devices can be severely threatened by the dissolution of alloy components.
ASU scientist Karl Sieradzki and two colleagues are working to help prevent such potential failures by devising methods that more accurately assess the risks of corrosion in certain types of alloys.
In a paper published in the December edition of the science journal Nature Materials, Sieradzki, Jason Rugolo and Jonah Erlebacher present their newly developed technique for predicting how long and under what conditions certain metallic alloys can be expected to resist corrosion – and what will happen if and when corrosion begins.
Sieradzki is a professor in ASU’s new School of Materials, which is jointly administered by the Ira A. Fulton School of Engineering and the College of Liberal Arts and Sciences. Rugolo, a past Goldwater Scholarship recipient earned an undergraduate degree in physics at ASU earlier this year and is now a graduate student in applied physics at Harvard University. Jonah Erlebacher is an associate professor of materials science and engineering at Johns Hopkins University.
In the paper titled “Length Scales in Alloy Dissolution and Measurement of Absolute Interfacial Free Energy,” the three authors describe their breakthrough in understanding the processes that govern solid-solution alloy corrosion and dealloying. It has led them to develop “a simple unifying picture” of conditions that cause the type of corrosion that can lead to stress-corrosion cracking, a significant factor in the failure of engineered structures.
Solid-solution alloys are composed of elements that are completely soluble in each other over a range of various compositions. If viewed under a microscope, only one type of crystal structure is observed.
“A beautiful and simple thermodynamic picture of selective dissolution emerges, which is similar to a nucleation process,” Sieradzki explains.
The onset of the electrochemical conditions causing dealloying or leaching of one of the elements from the solid-solution alloy is intrinsically linked to a fundamental parameter in thermodynamics called the interfacial free energy, he explains. This is because dealloying injects nano-scale porosity into the surface of a solid and the interfacial free energy is a measure of the work involved in this process.
The predictive models developed by Sieradzki, Rugolo and Erlebacher can aid progress in fundamental research in materials science, bioengineering, mechanical and environmental engineering.
Understanding and forecasting alloy corrosion is important in a number of areas in which metals are used. Many incidents of operational problems with nuclear power plants, oil pipelines or with aging aircraft are primarily “corrosion-induced failures,” Sieradzki says.
Accurately predicting alloy stability will become even more critical as the need increases for safe long-term storage of nuclear waste.
“We’ll need to know what’s going to be occurring in these alloys in storage tanks thousands and tens of thousands of years into the future,” Sieradzki says.
Medical technology also will benefit from these methods. The types of alloys the three researchers are working with are used in many kinds of stents – small tubes inserted in blood vessels to aid circulation – as well as in many new types of implantable biosensors.
Knowing more about the stability of the alloys in such devices will enable physicians to provide more effective long-term patient care.
Joseph Kullman, Ira A. Fulton School of Engineering
Joseph.Kullman@asu.edu
