Hydrogen Effects on Deformation and Fracture: Science and Sociology
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Hydrogen Effects on Deformation and Fracture: Science and Sociology H.K. Birnbaum Abstract The following article is an edited transcript based on the Von Hippel Award presentation given by Howard K. Birnbaum of the University of Illinois at UrbanaChampaign on December 4, 2002, at the Materials Research Society Fall Meeting in Boston. The award citation states, “Through innovative use of a wide range of novel experimental tools, Howard K. Birnbaum has made seminal contributions to our understanding of intrinsic point defects, hydrogen in metals, and grain-boundary segregation, especially as these effects relate to mechanical properties. He has also stimulated, directed, and influenced interdisciplinary research throughout the materials community.” This presentation summarizes the major phenomenological observations associated with hydrogen effects on fracture and the viable mechanisms that can account for these observations. It is shown that there are three fracture mechanisms that are consistent with the experimental observations and that the operative fracture mechanism depends on the type of system and the conditions under which it is exposed to hydrogen in aggressive environments. Keywords: deformation, ductility, embrittlement, fracture, hydrogen, transmission electron microscopy (TEM).
General Comments One may ask what could be sociological about a technical topic such as hydrogen effects on solids. My response is that in addition to discussing the science of hydrogen embrittlement, I will make a few comments on the nature of research funding at the beginning and at the end of this presentation. I would like to acknowledge the support of the Department of Energy, the National Science Foundation, and the Office of Naval Research for my work on hydrogen in metals over the past 25 years. I greatly appreciate the longevity of the support, which was necessary in order to understand the complex, interrelated set of phenomena underlying hydrogen embrittlement. Many aspects of the behavior of hydrogen in metals and the effects of hydrogen on the properties of metals needed to be elucidated prior to the development of a coherent understanding of the technologically important embrittle-
MRS BULLETIN/JULY 2003
ment problem. While such continued support was available in the past, I wonder whether these same agencies would choose to provide support for a sufficient period beyond the normal three-year funding horizon in the present funding climate. Many of the problems we deal with require support for periods longer than are currently available.
Introduction The effects of hydrogen on deformation and fracture are extremely important with respect to understanding material behavior in aggressive environments, where fracture often leads to disastrous consequences. Hydrogen is a ubiquitous element that enters materials from many different sources. It almost always has a deleterious effect on material properties. Hydrogen embrittlement was first recognized in about 1880, and these earliest
studies described most of the macr
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