Mobility of interstitial clusters in alpha-zirconium
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NTRODUCTION
IN recent years, significant attention has been paid to clusters of self-interstitial atoms (SIAs) formed in displacement cascades in metals irradiated with energetic particles because of the important role of SIA clusters in microstructure evolution. The successful application of the production bias model and its further developments[1] in the explanation of many features of radiation-induced microstructures, such as inhomogeneous damage near grain boundaries, decoration of dislocations by interstitial clusters and dislocation loops, rafts of dislocation loops, void lattice formation, etc., has initiated extensive studies of the properties of SIA clusters. So far, these studies have been concentrated mainly on metals with cubic lattices, e.g., fcc and bcc, where fundamental knowledge on structure and mobility of defect clusters and dislocation loops has been obtained.[2–7] However, many of the microstructure peculiarities noted previously have also been observed in irradiated hexagonal closed-packed (hcp) metals, such as Zr and Ti, which suggests that properties of defect clusters and dislocation loops in hcp and cubic metals have certain similarities. Recent cascade simulations by computer have demonstrated that small SIA clusters are formed in Zr.[8,9] The majority of them consist of collinear 具1120典 crowdions, and they exhibit one-dimensional (1-D) motion along the crowdion direction. Therefore, the formation mechanism in cascades and 1-D motion features look qualitatively similar to those observed in bcc and fcc structures. However, detailed information about the properties, N. de DIEGO, Senior Lecturer, is with the Department of Physics of Materials, Faculty of Physical Sciences, Complutense University, 28040 Madrid, Spain. Y.N. OSETSKY, University Research Fellow, and D.J. BACON, Professor, are with the Materials Science and Engineering, Department of Engineering, The University of Liverpool, Liverpool L69 3GH, United Kingdom. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
mechanism of motion, jump rate, migration energy, effect of cluster size, and morphology is not yet available for SIA clusters in hcp metals. To fill this gap, we have launched an extensive study of structure and properties of SIA clusters in an hcp crystal using atomic-level computer simulation techniques, such as molecular statics and molecular dynamics (MD). In the present article, we report some results on small clusters up to 30 SIAs. A principal aim is to compare such clusters in an hcp crystal with those in cubic metals. II. COMPUTATI
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