Atom probe field-ion microscopy: A technique for microstructural characterization of irradiated materials on the atomic
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I.
INTRODUCTION
IRRADIATION is well known to adversely affect the mechanical properties of materials. This degradation in mechanical behavior is related to irradiation-induced changes in the microstructure. The atom probe field-ion microscope is well suited to the characterization of the fine-scale features and the defects produced during irradiation due to its near atomic spatial resolution. Several field-ion microscopy (FIM) and atom probe field-ion microscopy (APFIM) investigations have been performed on neutron-, proton-, electron-, and ion-irradiated material. The materials examined have included pure elements, intermetallic compounds, model alloys, and complex commercial steels. The APFIM technique is able to provide information on the size and morphology of precipitates and voids, the chemistry of matrices and precipitates, solute clustering and partitioning, and segregation to interfaces, boundaries, and other defects. In this paper, an outline of the APFIM technique and a review of atom probe research on irradiated materials are presented. II.
THE ATOM PROBE I N S T R U M E N T
An atom probe is a combination of a field-ion microscope and a mass spectrometer. This combination permits atomic resolution images to be obtained in the field-ion microscope and the elemental identity of individual atoms to be determined in the mass spectrometer. Many refinements have been made to the basic instrument since its introduction in 1969 by MOiler et al. m Most modem instruments feature a combination of different variants of the atom probe in a single vacuum sys-
M.K. MILLER, Research Staff Member, is with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. M.G. HETHERINGTON, Research Fellow, is with the Department of Metallurgy and Science of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom. M.G. BURKE, Senior Research Scientist, is with the Westinghouse Research and Development Center, 1310 Beulah Road, Pittsburgh, PA 15235. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. METALLURGICAL TRANSACTIONS A
tern. The instrument, shown schematically in Figure 1, includes a field-ion microscope, a field-emission microscope, an energy-compensated atom probe, an imaging atom probe, and a pulsed laser atom probe. These variants permit a variety of analyses to be performed on metallurgical and semiconducting specimens. A complete description of these variants may be found elsewhereJ 2~ A. Specimen Preparation
Atom probe field-ion microscopy specimens are in the form of very sharp needles that are produced from bulk material with a combination of mechanical and chemical or electrochemical methods. Despite the fragile nature of the finished specimen, these methods have been s
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