Professor, Case Western Reserve University
12 PM, Tuesday, October 31st, 2017
1003 Kemper Hall
Abstract: The performance of alloy parts can often be substantially improved by “surface hardening.” For austenitic stainless steel and related alloys, this can effectively 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 carbides/nitrides. However, by driving the infusion process at a temperature chosen suitably low, it is possible to obtain uniform, precipitate-free solutions corresponding to ≈ 100,000 times the equilibrium solubility limit. Such “colossal supersaturation” with carbon or nitrogen within a typically ≈ 20 µm thick zone below the alloy surface enables dramatic improvements in surface hardness and wear 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.”
Biography: Educated as a physicist at the University of Göttingen, Germany, Frank Ernst received his diploma (MSc) in 1984, and was promoted to Doctorrerum naturalium (PhD) in physical metallurgy in 1987. Under the guidance of his advisor, Peter Haasen, he became 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 semiconductor heterointerfaces with one of the first atomic-resolution electron microscopes, he was appointed senior scientist at the Max-Planck-Institut für Metallforschung (Stuttgart) in 1989. In the Department of “Electron Microscopy and Internal Interfaces,” he led a group working on atomic-resolution TEM of grain boundaries 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. 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.