Microstructural evaluation of UF/sub 6/ cylinder valve bodies

During the installation of copper-alloy valves used for storage cylinders of uranium hexafluoride, cracking has been observed recently. To determine the cause of these cracks, the microstructure of these valves was examined in detail by optical metallography, Auger spectroscopy, transmission electron microscopy, and electron microprobe analyses. It was found that the cracks were associated with intergranular oxides. These films consisted primarily of aluminum-rich oxides. Auger spectroscopy also indicated that some areas were essentially pure aluminum. It was concluded that insufficient homogenization of the melt led to the retention of aluminum-rich areas and that these areas promoted extensive oxidation and cracking during further processing. It was recommended that a copper-aluminum master alloy be used in the future for alloying rather than pure aluminum as is the present practice, and that sufficient homogenization and stirring be employed during melting. 5 refs., 10 figs., 4 tabs.