Please see seminar notice below: MATERIALS SCIENCE AND ENGINEERING SEMINAR Mechanisms of Hydrogen Degradation in Metals By: Samantha Lawrence Ph.D. Prelim Exam – Part I Advisor: Prof. D. F. Bahr ABSTRACT Hydrogen is an important energy carrier; however, there are substantial barriers to effective hydrogen transport and storage. Degradation of metallic systems exposed to hydrogen (especially those used in pressure vessels, tanks, and pipelines of various energy industries) leading to unexpected catastrophic failures is particularly disturbing. Hydrogen is linked to a decrease in ductility, fracture strength, and fracture toughness in many metals (the phenomenon of hydrogen embrittlement). Three broadly grouped degradation mechanisms have been identified: (1) hydride formation, where brittle hydride precipitates ease fracture by providing low energy crack paths; (2) hydrogen-enhanced localized plasticity (HELP), where localized deformation increases in the presence of hydrogen due to a decrease in barriers to dislocation motion; and (3) hydrogen-enhanced decohesion (HEDE), where hydrogen reduces interfacial atomic bond strengths resulting in a sharp transition between ductile and brittle fracture. Hydrogen diffusion and subsequent capture at microstructural inhomogeneities, or traps, is required to establish a critical H-concentration prior to failure. Realizing that a “one‑size‑fits‑all” mechanism explaining observations of hydrogen embrittlement is unlikely, proposed degradation mechanisms are presented and future work geared toward understanding the interrelationships between the mechanisms is proposed. Date: Friday, April 12, 2013 Time: 11:30 A.M. Place: ARMS 1028 Lisa Stacey Secretary/Development Assistant Purdue University School of Materials Engineering 765/494-4100