MSE Seminar Series: Frank Ernst, Case Western Reserve University
Friday, May 5, 2017
2110 Chem/Nuc Bldg
Title: Alloy Surface Engineering by Concentrated Interstitial Solute
The performance of structural alloy parts can often be improved by "surface hardening." For austenitic stainless steel and related alloys, this can be accomplished by exposure to a gas phase that provides carbon or nitrogen to be incorporated on interstitial sites and diffuse into the alloy from the surface. Unfortunately, the typical equilibrium solubility limits for such interstitial solutes are very low and exceeding them can lead to highly undesired precipitation of second phases – e.g. carbides or nitrides. However, it was discovered that by driving the infusion process within a certain (small) window of low temperatures, it is possible to obtain uniform solutions with interstitial solute fractions of up to 15 at%, corresponding to ≈100,000 times the equilibrium solubility limit. Such “colossal supersaturation” with carbon or nitrogen within a ≈20m thick zone below the alloy surface enables dramatic improvements in surface hardness, wear resistance, fatigue resistance, and – surprisingly – corrosion resistance. This presentation will explain the underlying physical principles, describe conventional and new processing concepts, demonstrate the enormous improvements of alloy properties, and assess the technological potential of such “surface engineering by concentrated interstitial solute.
Frank Ernst joined the Department of Materials Science and Engineering at Case Western Reserve University (CWRU) in 2000. He is leading a research group focused on microstructure and micro-characterization of materials (https://goo.gl/OWsF9K). Current research interests include surface-engineering of structural alloys, metal plating, materials for energy conversion, heteroepitaxial interfaces, and advanced methods of microcharacterization. He is the Director of the Case Center for Surface Engineering (CCSE) and the Faculty Director of the Swagelok Center for Surface Analysis of Materials (SCSAM). In 2016, he was appointed Chair of the Department of Materials Science and Engineering. Educated as a physicist at the University of Göttingen, Germany, he received his diploma (MSc) in 1984 and was promoted to Doctor rerum naturalium (PhD) in physical metallurgy in 1987. Under the guidance of his advisor, Peter Haasen, he became deeply interested in materials microstructures and advanced techniques of TEM (transmission electron microscopy). After a period as postdoctoral research associate at CWRU in 1987/88, where he studied the structure of metal–oxide- and semiconductor heterointerfaces with one of the first atomic-resolution electron microscopes, he was appointed as senior scientist at the Max-Planck-Institut für Metallforschung (Stuttgart) in1989. In the Department of “Electron Microscopy and Internal Interfaces,” he headed a group working on atomic-resolution TEM of grain boundaries and heterointerfaces and developed the method of “quantitative HRTEM.” In 1997, he completed his habilitation with a professorial thesis on the “Structure of Heterointerfaces” and received the venia legendi from the University of Stuttgart. In 2000, he returned to CWRU as Professor.