Thick beryllium coatings by ion-assisted magnetron sputtering
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Craig Alford Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California 94550
Eric Chason Department of Engineering, Brown University, Providence, Rhode Island 02912
Andrew J. Detor Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California 94550
Tim Fuller General Atomics, San Diego, California 92186-5608
Alex V. Hamza Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California 94550
Jeff Hayes, Kari A. Moreno, and Abbas Nikroo General Atomics, San Diego, California 92186-5608
Tony van Buuren and Yinmin Wang Materials Science and Technology Division, Lawrence Livermore National Laboratory, Livermore, California 94550
Jun-jim Wu, Heather Wilkens, and Kelly P. Youngblood General Atomics, San Diego, California 92186-5608 (Received 13 July 2011; accepted 3 October 2011)
Thick (.150 lm) beryllium coatings are studied as an ablator material of interest for fusion fuel capsules for the National Ignition Facility. DC magnetron sputtering is used because of the relative controllability of the processing temperature and energy of the deposits. However, coatings produced by DC magnetron sputtering leak the fuel gas D2. By using ion-assisted DC magnetron, sputtered coatings can be made that are leak-tight. Transmission electron microscopy (TEM) studies revealed microstructural changes that lead to leak-tight coating. Ultrasmall angle x-ray spectroscopy is used to characterize the void distribution and volume along the spherical surface along with a combination of focused ion beam, scanning electron microscope, and TEM. An in situ multibeam optical stress sensor was used to measure the stress behavior of thick beryllium coatings on flat substrates as the material was being deposited.
I. INTRODUCTION
Beryllium is one of the ablator materials for use on the National Ignition Facility (NIF) due to its low x-ray opacity and high density. In particular, a graded copperdoped Be capsule is desired for ignition experiments. The capsule requires thick Be coatings (up to 160 lm), which are made on appropriate spherical mandrels, typically CH in composition.1 The coating has to be carried out at low temperatures to avoid any deformation of the mandrel to produce uniform wall thickness and smooth and spherical surface finish. The coating must be dense with low void fraction and be leak-free when filled with D2 fuel gas. DC magnetron sputtering is used to produce the coating because of the energetics of the depositing species and relative low coating temperatures.2 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.378 822
J. Mater. Res., Vol. 27, No. 5, Mar 14, 2012
The coating process has been described previously.2–5 Typically, Be coatings on a spherical surface show a consistent columnar microstructure with acceptable void content and size. However, the Be coatings suffer from sufficient interconnected porosity leading to rapid gas leakage. Measurem
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