Nanoporous Refractory Metals and Alloys: Synthesis, Characterization, and Irradiation

Abstract

Nanoporous materials are potentially advantageous in radiation environments, due to the high amount of ligament surface area that can act as a sink for defects produced during irradiation. A special technique, thermal dealloying in vacuum, is utilized for the formation of nanoporous refractory metals and has also been successfully applied to multi-principal element alloys. In-situ thermal dealloying experiments in the transmission electron microscope were performed on Nb-Mg alloys for fabrication of nanoporous niobium (np-Nb), where the precursor alloy composition range and dealloying temperature are the main parameters for controlling morphology and residual Mg in the final nanoporous structure. Applications of this processing approach will also be discussed for other refractory metals and a refractory multi-principal element alloy. Irradiation of np-Nb at different energies and varying total ion dose were performed on samples inside the TEM, creating defect structure within ligaments, as well as possible changes in the overall porous network structure. This presentation will cover the synthesis of np-Nb and its behavior during heavy ion irradiation, with emphasis on the ability of nanoporous structures to accommodate radiation damage. The development of nanoporous tungsten as the basis for a plasma-facing component in a fusion reactor environment will also be discussed.
 

Biography

William T. Bryan Professor of Materials Engineering John Balk is the Associate Dean for Research and Graduate Studies in the University of Kentucky (UK) College of Engineering. He works in the Department of Chemical and Materials Engineering, and he is also Director of the Electron Microscopy Center, which provides materials characterization services to the UK research community. Balk received his BS degree in 1995 from the University of California, Berkeley, where he double-majored in mechanical engineering and materials science & engineering. He received MS and PhD degrees in materials science & engineering from The Johns Hopkins University, in 1997 and 2000, respectively. Before coming to UK, he was a staff scientist at the Max-Planck-Institute for Metals Research in Stuttgart, Germany, where he also completed two years of post-doctoral work. The Balk research group works to understand structure-property relationships in the behavior of metals, alloys and ceramics. Characterization of advanced materials is the cross-cutting aspect of his research program. Current research activity focuses on materials development for applications that involve extreme conditions. His group works on combinatorial approaches to the development, characterization and testing of high entropy alloys, which represent a novel class of emerging materials for high-temperature structural applications. His group also explores the deformation mechanisms that operate in nanoporous metals and alloys, an area in which he has worked since coming to UK.